Review- Resistant Starch

Vol. 5, 2006—COMPREHENSIVE REVIEWS IN FOOD SCIENCE AND FOOD SAFETY 1© 2006 Institute of Food Technologists

ResistantStarch—

A ReviewM.G. Sajilata, Rekha S. Singhal,

and Pushpa R. Kulkarni

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KKKKKeyworeyworeyworeyworeywords: rds: rds: rds: rds: resistant staresistant staresistant staresistant staresistant starch (RS), functionalitych (RS), functionalitych (RS), functionalitych (RS), functionalitych (RS), functionality, for, for, for, for, formation, prmation, prmation, prmation, prmation, preparepareparepareparation, deteration, deteration, deteration, deteration, determination, digestibilitymination, digestibilitymination, digestibilitymination, digestibilitymination, digestibility, physiological, physiological, physiological, physiological, physiologicaleffects, applications, commercial sourceseffects, applications, commercial sourceseffects, applications, commercial sourceseffects, applications, commercial sourceseffects, applications, commercial sources

IntroductionFrom the early years of emergence of nutritional science, it has

been recognized that the ingested nutrients in the diet are notcompletely utilized in the body. An increasing volume of evi-dence suggests that with very few exceptions, only a proportion ofthe total ingested nutrients in a diet or food is available, and theterm “availability” has come into use for this proportion (South-gate 1989). The nutrients measured by chemical analysis may notalways be fully utilizable, mainly due to the indigestible cell walls,a bulky or dense structure, a low solubility, the presence of somecompounds inhibiting the digestion, as well as componentsabundantly present in plant foods such as dietary fiber, phyticacid, and tannic acid, which may significantly reduce the absorp-tion and utilization of some nutrients (Rosado and others 1987).During food processing, derivatization of nutrients and formationof cross linkages occur, thereby making the food inaccessible fordigestion or/and metabolism. Such parts of nutrients are also “un-available” (Erbersdobler 1989).

Starch, which is the major dietary source of carbohydrates, isthe most abundant storage polysaccharide in plants, and occursas granules in the chloroplast of green leaves and the amyloplastof seeds, pulses, and tubers (Ellis and others 1998). The relativelyrecent recognition of incomplete digestion and absorption ofstarch in the small intestine as a normal phenomenon has raisedinterest in nondigestible starch fractions (Cummings and Englyst1991; Englyst and others 1992). These are called “resistant starch-es,” and extensive studies have shown them to have physiologicalfunctions similar to those of dietary fiber (Asp 1994; Eerlingenand Delcour 1995). The diversity of the modern food industry andthe enormous variety of food products it produces require starch-es that can tolerate a wide range of processing techniques and

preparation conditions (Visser and others 1997). These demandsare met by modifying native starches with chemical, physical, andenzymatic methods (Betancur and Chel 1997), which may lead tothe formation of indigestible residues. The availability of suchstarches therefore deserves consideration. This review thereforefocuses on the availability of the major nutrient, that is, the starch,with special reference to RS.

Starch and its classificationChemically, starches are polysaccharides, composed of a num-

ber of monosaccharides or sugar (glucose) molecules linked to-gether with �-D-(1-4) and/or �-D-(1-6) linkages. The starch con-sists of 2 main structural components, the amylose, which is es-sentially a linear polymer in which glucose residues are �-D-(1-4)linked typically constituting 15% to 20% of starch, and amy-lopectin, which is a larger branched molecule with �-D-(1-4) and�-D-(1-6) linkages and is a major component of starch (BNF1990). Amylose is linear or slightly branched, has a degree of po-lymerization up to DP 6000, and has a molecular mass of 105 to106 g/mol. The chains can easily form single or double helices(Takeda and Takeda 1989). On the basis of X-ray diffraction stud-ies on oriented amylase fibers, the presence of type A and type Bamyloe is indicated (Figure 1, Galliard 1987). The structural ele-ments of type B are double helices, which are packed in an anti-parallel, hexagonal mode. The central channel surrounded by 6double helices is filled with water (36 H2O/unit cell). Type A isvery similar to type B, except that the central channel is occupiedby another double helix, making the packing closer. In this type,only 8 molecules of water per unit cell are inserted between thedouble helices. Amylopectin (107 to 109 g/mol) is highlybranched and has an average DP of 2 million, making it one ofthe largest molecules in nature. Chain lengths of 20 to 25 glucoseunits between branch points are typical. Its structure is often de-scribed by a cluster model (Figure 2). The cluster model gainedgreater credence when Hizukuri postulated that amylopectin

MS 20050127 Submitted 2/28/05, Revised 8/2/05, Accepted 10/29/05.The authors are with Food Engineering and Technology Dept., Inst. ofChemical Technology, Matunga, Mumbai – 400 019, India. Email:[email protected].

mailto:[email protected]

2 COMPREHENSIVE REVIEWS IN FOOD SCIENCE AND FOOD SAFETY—Vol. 5, 2006

CRFSFS: Comprehensive Reviews in Food Science and Food Safety

chains are either located within a single cluster or serve to con-nect 2 or more clusters (Hizukuri 1986; Thompson 2000). Shortchains (A) of DP 12-16 that can form double helices are arrangedin clusters. The clusters comprise 80% to 90% of the chains andare linked by longer chains (B) that form the other 10% to 20% ofthe chains. Most B-chains extend into 2 (DP about 40) or 3 clus-ters (DP about 70), but some extend into more clusters (DP about110) (Figure 2 and 3) (www.lsbu.ac.uk). On the basis of X-ray dif-fraction experiments, starch granules are said to have a semicrys-talline character, which indicates a high degree of orientation ofthe glucan molecules. About 70% of the mass of starch granule isregarded as amorphous and about 30% as crystalline. The amor-phous regions contain the main amount of amylose but also aconsiderable part of the amylopectin. The crystalline region con-sists primarily of the amylopectin.

Various ways to classify native starchesX-ray diffraction. Three types of starches, designated as type A,

type B, and type C, have been identified based on X-ray diffraction

patterns. These depend partly on the chain lengths making up theamylopectin lattice, the density of packing within the granules, andthe presence of water (Wu and Sarko 1978). Although type A andtype B are real crystalline modifications, type C is a mixed form. Theimportant features of the types of starches are as follows.

Type A. The type A structure has amylopectin of chain lengths of23 to 29 glucose units. The hydrogen bonding between the hy-droxyl groups of the chains of amylopectin molecules results inthe formation of outer double helical structure. In between thesemicelles, linear chains of amylose moieties are packed by forminghydrogen bonds with outer linear chains of amylopectin. This pat-tern is very common in cereals.

Type B. The type B structure consists of amylopectin of chainlengths of 30 to 44 glucose molecules with water inter-spread.This is the usual pattern of starches in raw potato and banana.

Type C. The type C structure is made up of amylopectin of chainlengths of 26 to 29 glucose molecules, a combination of type Aand type B, which is typical of peas and beans.

An additional form, called type V, occurs in swollen granules. X-ray diffraction diagrams of these starches are shown in Figure 4.

Based on the action of enzymesAccording to Berry (1986), starches can be classified according

to their behavior when incubated with enzymes without prior ex-posure to dispersing agents as follows.

Rapidly digestible starch (RDS). RDS consists mainly of amor-phous and dispersed starch and is found in high amounts instarchy foods cooked by moist heat, such as bread and potatoes.It is measured chemically as the starch, which is converted to theconstituent glucose molecules in 20 min of enzyme digestion.

Figure 1—Unit cells and arrangement of double helices (crosssection) in A-amylose (top) and B-amylose (bottom) (Galliard1987) Figure 2—Cluster model of amylopectin

Vol. 5, 2006—COMPREHENSIVE REVIEWS IN FOOD SCIENCE AND FOOD SAFETY 3

Resistant starch - a review

Slowly digestible starch (SDS). Like RDS, SDS is expected to becompletely digested in the small intestine, but for 1 reason or an-other, it is digested more slowly. This category consists of physi-cally inaccessible amorphous starch and raw starch with a type Aand type C crystalline structure, such as cereals and type B starch,

either in granule form or retrograded form in cooked foods. It ismeasured chemically as starch converted to glucose after a further100 min of enzyme digestion.

Resistant starch. The term “resistant starch” was first coined byEnglyst and others (1982) to describe a small fraction of starchthat was resistant to hydrolysis by exhaustive �-amylase and pul-lulanase treatment in vitro. RS is the starch not hydrolyzed after120 min of incubation (Englyst and others 1992). However, be-cause starch reaching the large intestine may be more or less fer-mented by the gut microflora, RS is now defined as that fraction ofdietary starch, which escapes digestion in the small intestine. It ismeasured chemically as the difference between total starch (TS)obtained from homogenized and chemically treated sample andthe sum of RDS and SDS, generated from non-homogenized foodsamples by enzyme digestion.

RS = TS – (RDS + SDS)

Based on the nutritional characteristicsThis classification is based on the extent of digestibility of the

starch as follows.Digestible starches. These include the starches digestible by

body enzymes, namely the rapidly digestible starches (RDS) andthe slowly digestible starches (SDS). RDS consists mainly of amor-phous and dispersed starch, found in high amounts in starchyfoods cooked by moist heat. Like RDS, SDS is expected to becompletely digested in the small intestine, but for 1 reason or an-other, it is digested more slowly.

Resistant starch. RS is indigestible by body enzymes. It is sub-divided into 4 fractions: RS1, RS2, RS3, and RS4. These are alsocalled as type I, II, III, and IV starches.

RS1 represents starch that is resistant because it is in a physical-ly inaccessible form such as partly milled grains and seeds and insome very dense types of processed starchy foods. It is measuredchemically as the difference between the glucose released by theenzyme digestion of a homogenized food sample and that re-leased from a nonhomogenized sample. RS1 is heat stable in mostnormal cooking operations and enables its use as an ingredient ina wide variety of conventional foods.

RS2 represents starch that is in a certain granular form and resis-tant to enzyme digestion. It is measured chemically as the differ-ence between the glucose released by the enzyme digestion of aboiled homogenized food sample and that from an unboiled, non-homogenized food sample. In raw starch granules, starch is tightlypacked in a radial pattern and is relatively dehydrated. This com-pact structure limits the accessibility of digestive enzymes, variousamylases, and accounts for the resistant nature of RS2 such as,ungelatinized starch. In the diet, raw starch is consumed in foodslike banana. RS1 and RS2 represent residues of starch forms, whichare digested very slowly and incompletely in the small intestine.

RS3 represents the most resistant starch fraction and is mainlyretrograded amylose formed during cooling of gelatinized starch.Most moist-heated foods therefore contain some RS3. It is mea-sured chemically as the fraction, which resists both dispersion byboiling and enzyme digestion. It can only be dispersed with KOHor dimethyl sulphoxide (Asp and Bjorck 1992). RS3 is entirely re-sistant to digestion by pancreatic amylases.

Therefore,

RS1 = TS – (RDS + SDS) – RS2 – RS3

RS2 = TS – (RDS + SDS) – RS1 – RS3

RS3 = TS – (RDS + SDS) - RS2 – RS1

RS4 is the RS where novel chemical bonds other than �-(1-4) or

Figure 3—(a) Shows the essential features of amylopectin.(b) Shows the organization of the amorphous and crystallineregions (or domains) of the structure generating the concen-tric layers that contribute to the “growth rings” that are vis-ible by light microscopy. (c) Shows the orientation of theamylopectin molecules in a cross section of an idealized entiregranule. (d) Shows the likely double helix structure taken upby neighboring chains and giving rise to the extensive de-gree of crystallinity in granule (www.lsbu.ac.uk).

Figure 4—X-ray diffraction diagrams of starches: type A (ce-reals), type B (legumes), and type V (swollen starch, Va: wa-ter-free, Vh : hydrated) (Galliard 1987)



�-(1-6) are formed. Modified starches obtained by various typesof chemical treatments are included in this category.

Table 1 outlines a summary of the different types of RS, theirclassification criteria, and food sources. In vitro digestibility ofstarch in a variety of foods (BNF 1990) is shown in Table 2.

Structure of RS

RS1

RS1 is the physically protected form of starch found in wholegrains (www.cerestarhealthand nutrition.com). Figure 5 shows mi-croscopic view of the physically inaccessible RS1 in cell or tissuestructures of partly milled grains, seeds, and vegetables.

RS2

In raw starch granules, starch is tightly packed in a radial pat-tern and is relatively dehydrated. This compact structure limits theaccessibility of digestive enzymes and accounts for the resistantnature of RS2 such as, ungelatinized starch. Figure 6 shows the RSgranules, that is, raw potato, banana, and high-amylose starch(www.cerestarhealthand nutrition.com).

RS3

RS3 represents retrograded starch. Thus, in the formation of RS3,the starch granule is completely hydrated. Amylose leaches fromthe granules into the solution as a random coil polymer. Uponcooling, the polymer chains begin to reassociate as double helices,stabilized by hydrogen bonds (Wu and Sarko 1978). The individualstrands in the helix contain 6 glucose units per turn in a 20.8 A° re-peat. The models for the double helices are left-handed, parallel-

stranded helices. A type A crystalline structure can be obtained ifRS is formed in gelatinized starch stored at high temperature (that is,100 °C) for several hours (Eerlingen and others 1993a). It has adense structure and only few water molecules in the monoclinicunit cell. Upon further retrogradation, the double helices pack in ahexagonal unit cell. The B form with hexagonal symmetry is moreopen. Water molecules (36 to 42 molecules per unit cell) in the Bstructure are located in fixed positions within a central channelformed by 6 double helices. The degree of polymerization (DP) ofamylose also affects the yield of RS3; it rises with DP up to 100 andthereafter remains constant (Eerlingen and others 1993b). A mini-mum DP of 10 and a maximum of 100 seems to be necessary toform the double helix (Gidley and others 1995). Schematic presen-tation of RS3 formed in aqueous amylose solutions depicted as mis-celle and lamella model is shown in Figures 7 and 8.

Structural features of in vivo RS (ingestion of retrograded high-amylose maize starch, complexed high amylose maize starch, beanflakes, or potato flakes) were assessed using the ileal contents of 4humans (Faisant and others 1993). For all samples, starch fractions,which escaped digestion in the small intestine, were composed of 3populations of �-glucans with proportions differing according tothe substrate. Small quantities of oligosaccharides made up the 1stpopulation, illustrating a limitation of absorption in the small intes-tine. The 2nd population, the main RS, consisted of retrogradedamylose of mean degree of polymerization (DPn) of about 35 glu-cose units with a melting temperature of 150 °C and exhibiting atype B pattern. Finally high-molecular-weight semicrystalline �-glu-cans were attributed to fragments of starch. This study showed thatsome potentially digestible starch could reach the colon and thatcrystalline fractions constituted only part of the starch that escapeddigestion in the human small intestine.

RS4

Structure of RS4 includes structures of modified starches ob-tained by chemical treatments like distarch phosphate ester (Fig-ure 9).

Table 1—Classification of types of resistant starch (RS), food sources, and factors affecting their resistance to digestion inthe colon (Nugent 2005)

Type of RS Description Food sources Resistance minimized by

RS1 Physically protected Whole- or partly milled grains and Milling, chewing seeds, legumes

RS2 Ungelatinized resistant granules Raw potatoes, green bananas, some Food processing and cooking with type B crystallinity, slowly legumes, high amylose corn hydrolyzed by �-amylase

RS3 Retrograded starch Cooked and cooled potatoes, bread, Processing conditions cornflakes, food products with repeated moist heat treatment

RS4 Chemically modified starches Foods in which modified starches have Less susceptible to digestibility due to cross-linking with been used (for example, breads, cakes) in vitro chemical reagents

Table 2—In vitro digestibility of starch in a variety of foods(BNF 1990)a

Foods % RDS % SDS % RS1 %RS2 %RS3

Flour, white 38 59 — 3 TracesShort bread 56 43 — — TracesBread, white 94 4 — — 2Bread, whole meal 90 8 — — 2Spaghetti, white 55 36 8 — 1Biscuits made with 34 27 — 38 Traces 50% raw banana flourBiscuits made with 36 29 — 35 Traces 50% raw potato flourPeas, chick, canned 56 24 5 — 14Beans, dried, freshly 37 45 11 Traces 6 cookedBeans, red kidney, 25 — — 15 60 cannedaValues are expressed as % of the total starch present in the food.

Figure 6—Structure of resis-tant starch type II (RS2)

Figure 5—Structure of resis-tant starch type I (RS1)



Functionality of RSRS has a small particle size, white appearance, and bland flavor.

RS also has a low water-holding capacity. It has desirable physico-chemical properties (Fausto and others 1997) such as swelling,viscosity increase, gel formation, and water-binding capacity,making it useful in a variety of foods. These properties make itpossible to use most resistant starches to replace flour on a 1-for-1 basis without significantly affecting dough handling or rheology.RS not only fortifies fiber but also imparts special characteristicsnot otherwise attainable in high-fiber foods (Tharanathan and Ma-hadevamma 2003). The functional properties and advantages ofcommercial sources of RS2 and RS3 (Nugent 2005) have beensummarized as follows. They are natural sources, bland in flavor,white in color, with fine particle size (which causes less interfer-ence with texture). They have high gelatinization temperature,good extrusion and film-forming qualities, and lower water-hold-ing properties than traditional fiber products. They allow the for-mation of low-bulk high-fiber products with improved texture, ap-pearance, and mouth feel (such as better organoleptic qualities)

compared with traditional high-fiber products; they increase coat-ing crispness of products and the bowl life of breakfast cereals.They are functional food ingredients lowering the calorific valueof foods and useful in products for coeliacs, as bulk laxatives andin products for oral rehydration therapy.

Some of these properties of RS have been successfully used in arange of baked and extruded products as described subsequently.

RS in bread-making for DF fortification(www.foodinnovation.com/functresist.pdf)

The physical properties of RS, particularly its low water-holdingcapacity, allow it to be a functional ingredient that provides goodhandling in processing and crispness, expansion, and improvedtexture in the final product. Bread is commonly fortified with di-etary fiber. However, dark color, reduced loaf volume, poormouthfeel, and masking of flavor are all negative attributes thatare often associated with high-fiber breads. A study was conduct-ed at the American Inst. of Baking (AIB) to evaluate the effect of RSon bread characteristics and to compare their performance to tra-ditional fibers. The study included cellulose, oat fiber, wheat fiber,and 2 commercially available RS with 23% (Hylon VII starch) and40% TDF (Novelose 240 starch) and a blend of oat fiber withNovelose 240 starch in a 50/50 ratio based on TDF contribution.Compared with oat fiber, cellulose, and wheat fiber, both RS had alower water-holding capacity, which is similar to that of flour. Al-though the water-holding capacity of the RS was lower than that ofthe other fiber sources, the quantity required to obtain the samelevel of TDF was greater. This raised the total water requirement ofthe RS dough. However, absorption of the RS doughs was lesscompared with the fiber doughs, despite a larger quantity of waterused. The lower dough absorption consequently had less impacton dough rheology and was closest to the white pan breaddough. Bread containing 40% TDF RS had greater loaf volumeand better cell structure compared with traditional fibers tested(Baghurst and others 1996).

Figure 7—Schematic presentation of enzyme resistant starchtype III (RS3) formed in aqueous amylose solutions. Micellemodel. Double helices are ordered into a crystalline struc-ture (C) over a particular region of the chain, interspersedwith amorphous, enzyme degradable regions.

Figure 8—Schemat-ic presentation ofenzyme-resistantstarch type IIIformed in aqueousamylose solutions.Lamella model.Lamellar structuresare formed by fold-ing of the polymerchains. The foldzones are amor-phous (A), while thecenter of the lamel-la is crystalline (C).

Figure 10—Behavior of amylose molecules during cooling ofa concentrated aqueous solution

Figure 9—Preparation of cross-bonded starch

http://www.foodinnovation.com/functresist.pdf



RS as a texture modifier in baked goodsOne way to ensure that the general population receives ade-

quate amounts of fiber in the diet is to fortify good-tasting foods thatnormally do not come to mind with fiber fortification but are ofteneaten as breakfast items or snacks. RS were incorporated in a vari-ety of baked goods, many of which include batter systems, such asin cakes, cake-like muffins, or brownies. In general, applicationtests showed that RS acts as texture modifier, imparting a favorabletenderness to the crumb. A low-fat, loaf cake was formulated withRS and various fibers to obtain approximately 3% TDF or 2.5 g of fi-ber per 80 g serving. These included a 40% TDF RS (Novelose 240starch), oat fiber, a blend of oat fiber with Novelose 240 starch in a50/50 ratio based on TDF contribution, and a 23% TDF RS (HylonVII starch). The baked cakes made with RS were similar to that con-taining oat fiber and the control in the amount of moisture loss afterbaking, height, specific volume, and density. A panel rated the 40%TDF RS loaf cakes as the best for flavor, grittiness, moisture percep-tion, and tenderness 24 h after baking.

RS as a crisping agentAmong other functional properties, RS can be used as an ingre-

dient that improves crispness in foods where high heat is appliedto a product’s surface during processing. French toast and waffles,especially frozen reheated types, represent foods in which surfacecrispness is desired. Tests were conducted to compare the func-tionality of RS and various fibers in a buttermilk waffle formula-tion. Based on the evaluation of the toasted waffles for initial crisp-ness, crispness after 3 min, moistness, and overall texture by atrained sensory panel RS waffle indicated greater crispness thancontrol or traditional fiber.

RS as a functional ingredient in other foodsAlong with textural enhancement, RS can improve expansion in

extruded cereals and snacks. Various cereals were formulated tocontain 40% TDF RS (Novelose 240 starch) alone and in combi-nation with oat fiber in ratios of 50/50 and 25/75 based onweight. The cereal with RS and no oat fiber had greater volumetricexpansion than the control. In blends with oat fiber, the cerealcontaining 75% of RS had better expansion than the one contain-ing only 50%. Dried pasta products containing up to 15% RS canbe made with little or no effect on dough rheology during extru-sion. Although the resultant pasta was lighter in color, a firm “aldente” texture was obtained in the same cooking time as a controlthat had no added fiber. RS may also be used in thickened,opaque health beverages in which insoluble fiber is desired. In-soluble fibers generally require suspension and add opacity tobeverages. Compared with insoluble fibers, RS imparts a less grittymouthfeel and masks flavors less.

Factors influencing the formation of RSSeveral factors influence the formation of RS.

Inherent properties of starchCrystallinity of starch. One of the causes of resistance to en-

zymes is the crystallinity of native type B starch granules as ob-served in the case of amylomaize starch and also the encapsula-tion of starch within plant cell or tissue structures. X-ray diffractionand differential scanning calorimetry studies on crystalline resi-dues from amylomaize starch samples have suggested that chainfragments packed in a type B crystalline structure with a slightlyenlarged crystal lattice contribute to formation of RS from amylo-maize starch. Any treatment that eliminates starch crystallinity(that is, gelatinization) or the integrity of the plant cell or tissuestructure (that is, milling) increases enzyme availability and reduc-es the content of RS, whereas recrystallization and chemical mod-

ifications tend to increase the RS. The modified food starches arepartially resistant to enzymes as a result of chemical modificationsinduced intentionally (Englyst and Cummings 1986; Bjorck andothers 1989; Schweizer and others 1990). Besides these, the cel-lular structure of plant foods influences the digestibility of starchin the small intestine as well as the intrinsic digestibility of a partic-ular physical form of starch.

Granular structure. A large variability in susceptibility to amy-lases shown by raw starch granules also influences RS formation.Potato starch and high amylose maize starch are known to bevery resistant in vitro and incompletely absorbed in vivo, whereasmost cereal starches are slowly but virtually completely digestedand absorbed in vivo (Holm and others 1987). The smaller sur-face-to-volume ratio of the large potato granules is probably im-portant. The nature of the granule surface also needs to be consid-ered; an adsorbed layer of non-starch material would effectivelyimpede the action of the enzyme (Ring and others 1988). Rawtepary starch is found to be more resistant to hydrolysis thanmaize starch, perhaps due to differences in granule structure andamylose content (Abbas and others 1987).

Amylose:amylopectin ratio. A higher content of amylose lowersthe digestibility of starch due to positive correlation between amy-lose content and formation of RS (Berry 1986; Sievert and Pomer-anz 1989b). The importance of the amylose:amylopectin ratio inthe postprandial glycaemic and insulinaemic responses to cornwas studied in commonly consumed corn products (Granfeldtand others 1995). The meals containing high amylose (70%) cornflour had an RS of 20 g/100 g DM than that containing ordinarycorn flour (25% amylose) that had RS of 3 g /100 g DM.

Retrogradation of amylose. When heated to about 50 °C, inthe presence of water, the amylose in the granule swells; the crys-talline structure of the amylopectin disintegrates and the granuleruptures. The polysaccharide chains take up a random configura-tion, causing swelling of the starch and thickening of the sur-rounding matrix such as, gelatinization—a process that rendersthe starch easily digestible. On cooling/drying, recrystallization(retrogradation) occurs. This takes place very fast for the amylosemoiety as the linear structure facilitates cross linkages by means ofhydrogen bonds. Figure 10 shows the formation of gel and mi-celle on cooling of a concentrated solution of amylose (Belitz andGrosch 1999). The branched nature of amylopectin inhibits its re-crystallization to some extent and it takes place over several days.

Retrograded amylose in peas, maize, wheat, and potatoes wasfound to be highly resistant to amylolysis (Ring and others 1988).The rate and extent to which a starch may retrograde after gelatini-zation essentially depends on the amount of amylose present. Re-peated autoclaving of wheat starch may generate up to 10% RS.The level obtained appeared to be strongly related to the amylosecontent, and the retrogradation of amylose was identified as themain mechanism for the formation of RS that can be generated inlarger amounts by repeated autoclaving (Berry 1986; Bjorck andothers 1990). During storage, the dispersed polymers of gelati-nized starch are said to undergo retrogradation to semicrystallineforms that resist digestion by pancreatic �-amylase. It forms a ma-jor portion of RS in wheat bread and corn flakes (Englyst andCummings 1985), whereas only 25% of the RS in cooked, cooledpotatoes can be accounted for as retrograded amylose. The di-gestibility of legume starch is much lower than that of cerealstarch, which is attributable to higher content of amylose in theformer. The digestibility of high amylose cereal starch is reportedto be significantly lower (Tharanathan and Mahadevamma 2003).

Native high-amylose starch is known to be high in type II RS (RS2) (Berry 1986), which is defined as starch in its native granularstate that is resistant to digestion in the small intestine. This aftercooking and cooling gives high yields of type III RS (Berry 1986;Sievert and Pomeranz 1989a) or retrograded starch (Englyst and



others 1992). Heating of RS preparation from amylomaize VII re-sulted in broad endothermic transition, which is ascribed to melt-ing of amylose crystallites (Sievert and Pomeranz 1989, 1990).Exothermic transitions during controlled cooling of isolated pota-to amylose fractions have been attributed to amylose chain asso-ciation. The formation of RS likewise has been attributed to the or-dering of amylose chains (Sievert and others 1991). Based on pre-vious studies of amylose behavior, it has been suggested that theexotherms observed during the cooling of either amylose or athermally treated RS preparation reflect chain association, whichmay involve amylose aggregation and gelation dominated by for-mation and subsequent lateral aggregation of type B double heli-ces in crystalline arrays (Gidley 1989; Gidley and Bulpin 1989;Sievert and Wursch 1993). Gelatinized waxy corn starch stored atvarying temperatures from 6 °C to 60 °C for 1 to 29 d alsoshowed reduced enzyme susceptibility to pancreatic �-amylaseand amyloglucosidase (Eerlingen and others 1994).

Influence of amylose chain length. Influence of amylose chainlength on enzyme RS formation was studied by Eerlingen and oth-ers (1993b) by hydrolyzing potato starch amylose to varying de-grees by incubation with barley �-amylase for different periods,and monitored by measuring the number of average chainlengths or degree of polymerization (DPn). The DPn of RS variedbetween 19 and 26 and was independent of the chain length ofthe amylose (DPn 40 to 610) from which it was formed. Resultssuggested that RS might be formed by aggregation of amylose he-lices in a crystalline �-type structure over a particular region of thechain (about 24 glucose units).

Linearization of amylopectin. Linearization of amylopectin oc-curs during the long low-temperature baking process due to theprolonged activity of intrinsic amylases in the dough, and isprominent in the presence of certain organic acids that is, inbread products baked with added lactic acid (Liljeberg and others1996). It has been reported to significantly increase RS formationduring wet-autoclaving (Berry 1986).

Heat and moistureWater content is an important factor that affects formation of RS.

Repeated heat/moisture treatment is associated with a decrease inthe hydrolysis limit of pancreatic �-amylase and increased forma-tion of RS. Maximum RS yield was obtained at a starch:water ratioof 1: 3.5 (w/w) (Sievert and Pomeranz 1989b) and a heat treatmentat 18% moisture gave increased levels of the degree of crystallini-ty of normal and waxy starches and thus reduced enzyme sus-ceptibility. However, at 27% moisture, starch degradation to someextent made areas of starch more accessible to enzyme attack.Thus, proper heat treatment could be used as a method of prepa-ration of RS (Franco and others 1995). In addition, higher temper-ature and less water results in type A configuration, whereas lowertemperature and high water content results in type B configuration(Wu and Sarko 1978).

Malshick-Shin and others (2003) determined solubility, watervapor sorption, and swelling characteristics for RS prepared fromwheat starch and linterized wheat starch by autoclaving and cool-ing and by cross-linking The experimental RS made from wheatstarch contained 10% to 73% RS versus 58% and 40% in com-mercial sources, Novelose 240 and 330 respectively, producedfrom high-amylose maize (corn) starch. In excess water, the exper-imental RS starches (except for the cross-linked wheat starch)gained 3 to 6 times more water than the commercial RS starchesat 25 °C, and 2 to 4 times more at 95 °C. All starches showed sim-ilar water vapor sorption and desorption isotherms at 25 °C andaw < 0.8. At aw 0.84 to 0.97, the RS made from wheat starch (ex-cept cross-linked wheat starch) showed approximately 10% high-er water sorption than the commercial RS.

RS determined in several selected cereals, legumes, and tubers

subjected to dry and wet heat treatment brought out higher RScontents in foods subjected to dry heat treatment compared withwet processed ones. Sorghum, green gram dhal, and green plan-tain showed highest RS content (5.51%, 5.81%, and 10.7%, re-spectively) (Platel and Shurpalekar 1994).

Interaction of starch with other componentsInteractions of starch with different components present in the

food system are known to influence the formation of RS as fol-lows.

Protein. Starch-protein interaction has been believed to reduceRS contents as observed in case of potato starch and added albu-min when autoclaved and subsequently cooled at –20 °C (Escar-pa and others1997).

Dietary fiber. Insoluble dietary fiber constituents such as cellu-lose and lignin have been shown to have minimal effects on RSyields compared with other constituents such as potassium andcalcium ions and catechin (Escarpa and others 1997).

Enzyme inhibitors. Polyphenols, phytic acid, and lectinspresent mainly in leguminous seeds, have been reported to inhib-it in vitro starch hydrolysis and to lower the glycemic index (Th-ompson and Yoon 1984). Tannic acid significantly inhibits bothamylases and intestinal maltase activity (Bjorck and Nyman 1987).Indigestible residues from black beans (Phaseolus vulgaris cv. Tac-ari gua), green beans (P. vulgaris), carrots (Daucus carota), andrice bran (Oryza sativa) are all reported to inhibit pancreatic �-amylase in vitro (Moron and others 1989). Since amylolysis is in-hibited by phytic acid, a decrease in phytate content increasesstarch digestibility (Thompson and Yoon 1984). Contradictory in-formation exists in the literature on this aspect. The autoclavingand subsequent cooling of potato starch and catechin was foundto significantly reduce the yields of RS, whereas the addition ofphytic acid to potato starch reduced the RS contents to a minorextent (Escarpa and others 1997) compared with the RS formedfrom potato starch with no added constituent. The reasons for thesame are still not clear.

Ions. The yields of RS in potato starch gels decrease in the pres-ence of calcium and potassium ions compared with those with noadded constituent (Escarpa and others 1997), presumably due tothe prevention of formation of hydrogen bonds between amyloseand amylopectin chains caused by adsorption of these ions.

Sugars. The addition of soluble sugars such as glucose, mal-tose, sucrose, and ribose has been found to reduce the level ofcrystallization and subsequently reduce the yields of RS (Buchand Walker 1988; I’Anson and others 1990; Kohyama and Nishi-nari 1991). The mechanism of retrogradation inhibition was con-sidered as the interaction between sugar molecules and the starchmolecular chains, which change the matrix of gelatinized starch(the sugars act as anti-plasticizers and increase the glass transitiontemperature).

The role of sugars on the formation of RS in starch gels (RS typeIII) was studied by Eerlingen and others (1994). Sugars influencedthe RS levels in starch gels only when added in high concentra-tion (final starch-water-sugar ratio of 1:10:5 w/w). In wheat starchgels, the RS yields decreased from approximately 3.4% to 2.8% inthe presence of sucrose or glucose, and to 2.5% in the presenceof ribose or maltose. An increase in RS yield was observed withhigh-amylose corn starch. The experiments showed that the differ-ences in gelatinization temperature, lipid content, and apparentamylose content of the 2 starches were not the main causes of thedifferent impact of sugars on RS yields.

Lipids, emulsifiers. In a study, amylomaize VII starch, auto-claved at 125 °C, was reacted during cooling below 100 °C withlysophosphatidyl choline (LPC), sodium stearoyl lactylate (SSL),and hydroxylated lecithin (OHL) (Czuchajowska and others1991). Differential scanning calorimetry (DSC) peaks at around



95 °C to 110 °C indicated formation of amylose-lipid complexes,and at about 155 °C indicated the presence of enzyme-resistantstarch (RS). Yields of RS from complexed samples isolated by ther-mostable bacterial �-amylase or amyloglucosidase were lowerthan yields of RS from the autoclaved and cooled control. Forma-tion of complexes competes with amylose chains involved in gen-eration of RS. Amylose-lipid complexes are enzyme-degradable,and an increase in complexed amylose reduced yields of RS.Amylose recrystallization in RS formation is competitively affectedby complexation of amylose with LPC and SSL. Results of X-raydiffraction powder crystallography were in agreement with DSCmeasurements. Complexes of amylose with LPC, SSL, and OHLgave type V patterns; enzymic hydrolysis of the complexes yield-ed type B RS structures. However, the viewpoint differs among sci-entists working in this area. While some workers believe amylose-lipid complex to reduce the formation of RS, others believe theamylose-lipid complex itself to be a form of RS.

From studies on isolated barley starch autoclaved with sodiumstearoyl lactylate (SSL), distilled monoglycerides, diacetyl tartaricacid esters of mono-diglycerides (DATEM), and ethoxylated mono-glycerides (bakery additives), it is postulated that amylose crystalli-zation (as measured by enthalpies of the 158 °C endotherm) that isinvolved in the formation of RS is competitively affected by its com-plexation with lipids (Szczodrak and Pomeranz 1992).

Effect of citric acid and 2 emulsifiers SSL and DATEM on forma-tion and structure of RS during extrusion of cornstarch and guargum were studied (Adamu 2001). X-ray diffraction of the extrudedstarches gave a V-diffraction pattern indicating the formation ofamylose-lipid complexes. Purification of the isolated RS by sizeexclusion high-performance liquid chromatography (HPLC) indi-cated the additives to have a substantial effect on molecularweight; DATEM and SSL increased molecular weight of RS, whilecitric acid decreased it.

The influence of endogenous lipids on the formation of RS fromwheat starch showed defatting to decrease the RS content (Eerlin-gen and others 1994). When SDS was added to defatted wheat oramylomaize VII starch, RS yields decreased substantially. X-ray dif-fraction and DSC showed that amylose-lipid complexes wereformed in the presence of both endogenous and added lipids(SDS). A similar behavior has been reported on addition of lipids(Eliasoson and others 1988) such as olive oil (Escarpa and others1997). Thus, less amylose was available for interactions leading tothe formation of double helices and RS. Adding SDS to the starchalso caused a difference in RS quality.

Amylose-lipid complexes can also be formed during food pro-cessing (autoclaving and cooling). Lecithin, palmitic acid, oleicacid, and soya bean oil affect retrogradation to a lower extent thanmonoglycerides. Nevertheless, these authors found that pure po-tato amylose and oleic acid formed complexes highly resistant toamylolysis (Mercier 1980).

Processing conditionsProcessing techniques may affect both the gelatinization and ret-

rogradation processes, influencing RS formation. This fact is of greatimportance for the food industry since it offers the possibility of in-creasing the RS content of processed foods and foodstuffs. Baking,pasta production, extrusion cooking, autoclaving, and so forth areknown to influence the yield of RS in foods (Siljestrom and Asp1985; Bjorck and Nyman 1987; Siljestrom and others 1989; Muirand O’Dea 1992; Rabe and Sievert 1992). Highly processed cerealflours and foods made from the flours, such as pasta, contain muchlower levels of RS, averaging only about 1.5% to 8% RS on a drybasis. Since the crystalline structure of starch in legumes (type C) ismore stable compared with the crystal structure in cereal grains(type A) (Ring and others 1988), processing cereal grains results in alarge decrease in RS content, while legumes are excellent sources

of RS. Cooking under conditions of high moisture and temperaturecan significantly lower the RS content by disrupting crystallinestructure. Increasing the levels of RS can be done in other condi-tions, such as extrusion followed by cooling to induce crystalliza-tion (Haralampu 2000). The RS contents in various processed foodsamples have been reported (Siljestrom and Bjorck 1990; Parchureand Kulkarni 1997; Kavita and others 1998).

Thermal processingSteam cooking. Steam cooking helps in production of RS. Starch-

es isolated from several steam-heated legumes were rich in indi-gestible RS (19% to 31%, DM basis), which was not observed inraw beans (Tovar and Melito 1996). Similarly, RS measured directlyin conventionally and high-pressure steamed beans were 3 to 5times higher than in the raw pulses, suggesting retrogradation to bemainly responsible for the reduction in digestibility. Prolongedsteaming as well as short dry pressure heating decreased the enzy-mically assessed total starch content of whole beans by 2% to 3%(DM basis), indicating that these treatments may induce formationof other types of indigestible starch (Tovar and Melito 1996).

Autoclaving. Autoclaving results in increase in RS. Autoclavedwheat starch has 9% RS compared with less than 1% in un-cooked wheat starch (Siljestrom and Asp 1985). Autoclavedwheat starch contained 6.2% RS (of dm); this increased to 7.8%after 3 further reboiling/cooling cycles (Bjorck and others 1987).Quantitative and qualitative influence of incubation time and tem-perature of autoclaved starch on RS formation was studied by Eer-lingen and others (1993a). In another study, white flour subjectedto repeated autoclaving and cooling cycles showed an increase intotal dietary fiber >3 times that of bread flours and 4 times that ofpastry flours (Ranhotra and others 1991b). The increase was pri-marily due to the formation of RS. Investigations on the formationof enzyme-resistant starch (RS) during autoclaving and cooling bySievert and Pomeranz (1989a) showed highest yield (21.3%) to beobtained from amylomaize VII starch (70% amylose). Formation ofRS in amylomaize VII starch was affected by the starch/water ratio,autoclaving temperature and number of autoclaving-cooling cy-cles. The number of cycles exerted the most pronounced effect onRS; increasing the number of cycles to 20 raised RS level to>40%. Furthermore, the thermoanalytical data suggested thatamylose-lipid complexes were not involved in the formation ofRS. Yields in excess of 20% RS can be obtained from autoclavedamylomaize starch containing 70% amylose. They can be raisedto levels of 40% by increasing the number of autoclaving-coolingcycles up to 20 (Eerlingen and Delcour 1995).

The extent of RS formation in commercially available auto-claved corn, potato, and leguminous products and in autoclavedpurees intended for consumption by infants aged 3 to 8 mo wasinvestigated by Siljestrom and Bjorck (1990). RS levels found (g/100 g DM) were as follows: 0.8 to 2.4 in purees, 0.2 to 3.2 incanned legumes, 1.9 in canned potatoes, 0.5 and 0.9 in reconsti-tuted dried potatoes, <0.1 in canned corn, and 1.1 in cornflakes.

Native starch (NS) extracted from wheat and subjected to 5 au-toclaving and cooling cycles was found to contain 11.5% RS,which was measured as insoluble fiber; NS contained 0.5% RS(Ranhotra and others 1991a). Heat-moisture treatment (autoclav-ing at 121 °C) with subsequent cooling was used to produceamylase-resistant starch (RS) from purified high-amylose starchsamples. The formation of RS in barley starch was strongly affectedby the number of autoclaving-cooling cycles; increasing the num-ber of cycles from 1 to 20 raised the RS yield from 6% to 26%(Szczodrak and Pomeranz 1991).

Parboiling. Parboiling increases RS production. In studies on 5rice varieties, differing in amylose content, the in vitro and in vivoRS levels were low and positively correlated with amylose content(Eggum and others 1993). Higher RS starch levels were found in



cooked and parboiled-cooked rice than in raw rice; waxy ricehad very low values. Higher contents of RS have been reported inparboiled rice than raw white rice, which also increased by cool-ing or freezing (Marsono and Topping 1999).

Baking. Baking increases RS content. In a study to evaluate the ef-fect of baking on RS formation, white bread was baked and dividedinto 3 fractions (crumb, inner crust, and outer crust) (Westerlundand others 1989). Starch levels were found to be highest in doughand lowest in outer crust after baking for 35 min. RS levels werelowest in dough and highest in crumb after baking for 35 min. Alow-temperature, long-time baked product contained significantlyhigher amounts of RS than bread baked under ordinary conditions(Liljeberg and others 1996). Addition of lactic acid increased RS re-covery further whereas malt had no impact on RS yield. The highestlevel of RS was noted in long-time baked bread based on high-amylose barley flour. RS isolated from wheat-based foods such aschapatti and phulka was structurally characterized as a linear 1, 4-linked �-D-glucan essentially derived from retrograded amylosefraction, which was dependent on the severity of the processingtreatments as well as the levels of gluten and damaged starch in thewheat flour (Tharanathan and Tharanathan 2001).

Extrusion cooking. Effect of extrusion cooking, at different tem-peratures (90, 100, 120, 140, or 160 °C), moisture contents(20%, 25%, 30%, 35%, or 40%) and screw speeds (60, 80, or100 rpm), was investigated on the formation of RS of type 3 (RS3)in hull-less barley flours from CDC-Candle (waxy) and Phoenix(regular). The RS3 content of the native flours, in general, de-creased by extrusion cooking, but not significantly. Storage of ex-truded flour samples at 4 °C for 24 h before oven drying slightlyincreased RS3 content (Faraj and others 2004). With pearl barleyused as the primary material in tests designed to optimize the pro-duction of RS by extrusion an extrusion temperature of 150 °Cand a barley moisture content from 17.5% and 22.5% moisture,followed by cold storage at –18 °C gave the best results (Gebhardtand others 2001).

Corn starches with and without guar gum [10% (w/w)] and 2%(w/w) of diacetyl tartaric acid ester of monoglyceride, sodiumstearoyl-2-lactylate or citric acid, respectively, were extrusion-cooked in a twin-screw extruder at 18% moisture, 150 °C, and 180rpm screw speed (Adamu 2001). The formation of RS in extrudedcorn starch was found to be strongly affected by the addition ofgum and the different food additives. X-ray diffraction of the extrud-ed starches gave a V diffraction pattern indicating the effect of extru-sion cooking and amylose-lipid complexes. Enzymatic digestiondid not affect the V structure, which could apparently be attributedto extrusion cooking. Purification of the isolated RS by size exclu-sion-HPLC showed a dependence of molecular weight on the add-ed additives. Results of differential scanning calorimetry and X-raydiffraction suggest that amylose-lipid complexes could also be in-volved in the formation of RS in extruded cornstarch.

Pyroconversion. Pyroconversion of starch increases RS con-tent. Lima bean (Phaseolus lunatus) starch was modified using py-roconversion, the optimum product being recovered from nativestarch treated with a 160:1 starch/HCl ratio, at 90 °C for 1 h, re-sulting in starches containing 49.5% indigestible starch (Testerand others 2004). Starch pyrodextrinization decreased theamount of enzymically available starch through formation of atyp-ical glycosidic bonds that are not digested by the amylases andmaltooligosaccharidases in the small intestine of humans.

Microwave irradiation. Microwave irradiation improves the di-gestibility of tuber starches, which could be accompanied byphysicochemical and structure changes (www.man.poznan.pl).Microwave cooking of legumes such as chickpeas and commonbeans produced a redistribution of the insoluble nonstarchpolysaccharides to soluble fraction, although the total nonstarchpolysaccharides were not affected. This was evaluated by assess-

ing the physicochemical, nutritional, and microstructural modifi-cations in starch and nonstarch polysaccharides (Marconi andothers 2000). The RS level decreased from 32.5% of total starch inraw chickpeas and beans, respectively, to about 10% in cookedsamples with a concomitant increase in the level of rapidly digest-ible starch from 35.6% and 27.5% to about 80%.

Studies on effects of different heat treatments (cooking, micro-wave cooking, pressure cooking) on the rate of hydrolysis, hy-drolysis index, and glycaemic index values of kudzu starch andcornstarch showed increase in digestible starch and decrease inRS following heat treatment. The rate of hydrolysis of kudzu starchand cornstarch increased following heat treatment, especially aftermicrowaving (Geng and others 2003).

Miscellaneous treatments.Milling. Leguminous seeds, in which cell structures are pre-

served after cooking (that is, bread with whole seeds); bean flourwith intact cells (Schweizer and others 1990); foods containinglarge particles such as bread with whole seeds have lower physi-cal accessibility of starch to amylase action, and thereby contrib-ute to higher RS contents. In some foods, physically inaccessiblestarch is likely to be an important fraction of the total starch that isresistant to digestion in vivo. Schweizer and others (1990) foundevidence of 20% starch malabsorption from a diet containingbean flour with intact cells. About half of the malabsorbed starchwas retrograded amylose. The precooked flours (PCF) preparedfrom dried lentils and beans, rich in intact cells filled with starchgranules, indicated that they contained important quantities of RS,such as retrograded amylose (3% to 9%, DM).

Germination. Germination is shown to decrease the RS contentin bengal gram, field beans, cow pea, and green gram (Kavita andothers 1998).

Fermentation. Fermentation reduces RS content. Flour from sor-ghum cv. Tabat was mixed with water and previously fermenteddough starter, and fermented at 37 °C for a maximum of 36 hshowed an increase in the in vitro starch digestibility and a de-crease in the content of RS and total starch (Abd-Elmoneim andothers 2004). RS formation has also been shown to decrease in thefermented products, idlis and dhoklas (Kavita and others 1998).

Storage conditionsGenerally, RS increases on storage, especially low-temperature

storage. Cold storage seems to support an increase in RS content.Whole corn bread and corn bread crumb, when stored at differ-ent temperatures (–20 °C, 4 °C, or 20 °C) for 7 d showed RS con-tents to reach a maximum between 2 and 4 d at all storage tem-peratures, after which they decreased (Niba 2003). Lowest RS lev-els in whole corn bread were found after storage at –20 °C (2.18g/100 g) for 7 d.

A comparison of masa and fresh and stored tortillas from com-mon and Costeno corn varieties showed that Costeno had higherdigestible starch and total dietary fiber contents than its commoncounterpart. During storage of both types of tortilla, digestiblestarch contents decreased, whereas those of RS starch increased(Mora-Escobedo and others 2004). Studies on the influence ofcold storage on in vitro starch digestibility of tortillas showed adecrease in available starch content in tortillas after 48 h of coldstorage, which was concomitant with increased total RS levels(Agama-Acevedo and others 2004). These changes were duemainly to retrogradation, as indicated by increased retrogradedresistant starch (RRS) levels which accounted for the major portionof the total RS. Although amylolysis patterns for fresh and 72 h–stored tortillas were similar, lower digestion rates were observedfor stored samples.

RS contents of gelatinized samples of corn, ragi, rice, sago, andpotato flours increased on low-temperature storage and de-

http://www.man.poznan.pl



creased on reheating the samples. Cooked food samples of rice,unleavened bread, potato, Bengal gram, and green gram alsoshowed increased RS formation on storage. There was no signifi-cant increase in RS content of stored decorticated legumes (ben-gal gram, green gram, and red gram), whereas horse gram andlentils showed lesser RS on storage in comparison with fresh sam-ples. Increase in RS was reported for gelatinized samples of corn,wheat, ragi, rice, sago, and potato flours on low-temperature stor-age. A 27% increase in RS of cooked rice was observed whenstored at 4 °C (Johansson and Siljestrom 1984). The longer the du-ration of storage of gelatinized wheat flour, the greater was the for-mation of RS (Kavita and others 1998). Rice stored at –20 °C retro-graded more than rice stored in the refrigerator (Mitsuda 1993).

Preparation of RSRS can be prepared by using heat treatment, enzyme treatment,

combined heat treatment and enzyme treatment, and chemicaltreatment.

Heat treatmentHeat treatment of starch to various extents leads to formation of

RS. RS can be obtained by cooking the starch above the gelatini-zation temperature and simultaneously drying on heated rolls likedrum driers or even extruders. The gelatinization of starch gran-ules by heat processing strongly influences their susceptibility toenzymatic hydrolysis. In a high-moisture environment, amyloseleaches from the granules, increasing the solubility of starch andthereby its susceptibility (Holm and others 1988).

Good yields of RS can be obtained by gelatinizing starch at120 °C for 20 min, followed by cooling to room temperature (Gar-cia-Alonso and others 1999). The starch gels are then frozen over-night at –20 °C and dried at 60 °C before milling.

Many combinations of time and temperature treatments havebeen used to make type III RS from various sources of nativestarch. Even for starches with normal amylose levels, it is recog-nized that cooking at >100 °C can increase the yield of type III RS.The temperature treatments have included autoclaving the starchat 110 °C (Berry 1986), at 121 °C (Berry 1986; Bjorck and others1987; Sievert and Pomeranz 1989; Sievert and Wursch 1993b), at127 °C (Berry 1986; Bjorck and others 1987), at 134 °C (Berry1986; Bjorck and others 1987; Russell and others 1989; Sievertand Pomeranz 1989), or at 148 °C (Sievert and Pomeranz 1989)for periods ranging from 30 min to 1 h.

An enzyme-RS type III, which has a melting point or endothermicpeak of at least about 140 °C, as determined by differential scan-ning calorimetry (DSC) can be produced in yields of at least 25%by weight, based on the weight of the original starch ingredient(Haynes and others 2000). A gelatinization stage, nucleation/prop-agation stage, and preferably a heat-treatment stage are required toproduce reduced calorie starch-based compositions that containthe enzyme-resistant starch. It is produced using crystal nucleationand propagation temperatures, which avoid substantial productionof lower melting amylopectin crystals, lower melting amylose crys-tals, and lower melting amylose-lipid complexes. The nucleatingtemperature used is above the melting point of the amylopectincrystals. The propagating temperature used is above the meltingpoint of any amylose-lipid complexes but below the melting pointof the enzyme RS. The high melting point of the enzyme RS permitsits use in baked good formulations.

Partial acid hydrolysis (PAH) of a high-amylose corn starch (ae-VII) enhances the effects of hydrothermal treatments used to pro-duce granular RS, which is stable to further heat treatment at at-mospheric pressure (Brumovsky and Thompson 2001). PAH ofae-VII starch involved heating 35% (w/v) starch suspensions with1% (w/w) HCl at 25 °C for up to 78 h. PAH followed by heat mois-

ture treatment tended to increase yield of boiling-stable granularRS to the maximum of 63.2%.

Selective heat treatment of high amylose starch in the presenceof agents inhibiting the swelling of starch like alkali and alkalineearth metal salts of halides, sulfates, and phosphates yield granu-lar RS with high dietary fiber.

Recently, pyrodextrinization has been recognized as a way ofproducing a RS that is water-soluble and has non-starch linkages(Laurentin and Edwards 2004). Pyroconversion refers strictly to themodification of dry starch through heat treatments, with or withoutaddition of acids. Acids used include hydrochloric acid at 0.15%(based on starch dry weight) and orthophosphoric or sulfuric acidsat 0.17% (Wurzburg 1995). Commercial pyrodextrins are generallyproduced by heating dry, acidified starch in a reactor with agitation.Acid may be sprayed on the starch to facilitate hydrolysis and trans-glycosidation. Depending on reaction conditions, pyroconversionproduces a range of products that vary in digestibility, availablestarch, viscosity, cold-water solubility, swelling power, color, andstability (Ohkuma and Wakabayashi 2001). The production of indi-gestible dextrins or pyrodextrins by heat-treating potato starch inthe presence of an acid and then refining the product has been de-scribed (Ohkuma and others 1994, 1995).

Enzymic treatmentThe possibility of preparing a RS concentrate from isolated pea

starch was investigated, and sorption of hydrophobic substances(indicative of health-benefiting properties) by such a concentratewas studied by Soral and Wronkowska (2000). By use of a thermal-ly stable �-amylase, a preparation of up to 70% RS containing amixture of mineral and organic N compounds was obtained. Thepea RS concentrate had an affinity to bile acid, deoxycholic, andcholesterol; however, its affinity to cholesterol was not as efficient asthat of native pea starch. The results concluded that the pea RS con-centrate may be potentially used as a food component in specialdiets, or for preventive, prophylactic, and therapeutic purposes.

Readily fermentable heat-stable RS of optimal chain length frompoly-1,4-�-D-glucan useful in various functional foods can beobtained by in vitro synthesis by adding an enzyme extract con-taining the amylosucrase of Neisseria polysaccharea to sucrosesolutions, followed by incubation at 37 °C over several hours(Buttcher and others 1997).

A method has been discovered to produce an RS product thatretains the same cooking quality as found in untreated rice starchor flour, but has a higher percentage of starch resistant to �-amy-lase digestion (King and Tan 2005). This method uses a debranch-ing enzyme, that is, pullulanase, to digest the starch, but does notrequire pretreating the starch source before enzymatic treatment.This method produced RS from low amylose starches, rice starch(24%), and rice flour (20%). Surprisingly the RS product formedby this method retained the pasting characteristics of the untreat-ed flour or starch and was heat stable. This method may also beused to produce RS from other botanical sources, that is, corn,wheat, potato, oat, barley, tapioca, sago, and arrowroot.

Heat and enzyme treatmentPreparation of RS to be used as a food-grade bulking agent, by

retrogradation of starch followed by enzymatic or chemical hy-drolysis to reduce or remove the amorphous regions of retrograd-ed starch (Iyengar 1991). RS can be prepared from high amylosestarch by gelatinization followed by treating the slurry with de-branching enzymes like pullulanase and isolating the starch prod-uct by drying/extrusion. Controlled heat treatment of starch so asto achieve swelling and at the same time retain its granular struc-ture followed by enzymatic debranching (Haralampu and Gross1998) and annealing at suitable temperature followed by dryingproduces RS. These RS find applications in a variety of foods and



beverage products.Purified RS products having at least 50% RS content can be

produced by forming a water-starch suspension wherein the ratioof starch to water is approximately 1:2 to 1:20, heating the water-starch suspension in an autoclave at temperatures above 100 °C.to ensure full starch gelatinization and then cooling to allow amy-lose retrogradation to take place. It is reported that best resultswere obtained at a temperature of 134 °C, with 4 heating andcooling cycles and a starch:water ratio of 1:3.5. The RS was puri-fied by comminuting the starch gel and mixing it with an amylaseto digest non-RS fractions, leaving RS. The amylase is inactivatedby heat treatment above 100 °C (Pomeranz and Sievert 1990).

For the preparation of a fragmented starch precipitate for use inreduced-fat foods, a debranched amylopectin starch is precipitatedand then fragmented. The debranched amylopectin starch may bederived from a starch that contains amylopectin, for example, com-mon corn starch and waxy maize starch, by gelatinizing the starch,followed by treatment with a debranching enzyme, such asisoamylase or pullulanase, and precipitation of the debranchedstarch. To form the precipitate, the solution is cooled to ambienttemperature, to reduce the solubility of the debranched starch. Theprecipitate may then be heated to about 70 °C, while in contactwith a liquid medium, to dissolve at least a portion of the precipi-tate. Reprecipitation by cooling of the suspension/solution maythen be employed. Repetition of the dissolving and the reprecipita-tion tends to improve the temperature stability of the resulting aque-ous dispersion as was observed on repeating the cycle of heatingand cooling, a total of 8 times (Harris and others 1994, 1995).

A process for increasing the amount of amylase-RS (to a mini-mum of 15%) in high amylose starch, such as Hylon V or HylonVII consisted essentially of gelatinization of a starch slurry, enzy-mic debranching of the starch, and isolation of the starch productby extrusion or drying. A further increase in amylase-resistantstarch was obtained by addition of an inorganic salt to de-branched starch before isolation (Chiu and others 1994).

Chemical treatmentIn type IV RS, the enzyme resistance is introduced by modifying

the starch by crosslinking with chemical agents (Haynes and others2000). Crosslinked starches are obtained by the reaction of starchwith bi- or polyfunctional reagents like sodium trimetaphosphate,phosphorus oxychloride, or mixed anhydrides of acetic acid anddicarboxylic acids like adipic acid. Cross-linking carried out by sul-phonate and phosphate groups between various starch moleculesinvolves their hydroxyl group thus bringing resistance to amylolyticattack on the starch molecule. Figure 9 shows the preparation ofdistarch phosphate ester (Hamilton and Paschall 1967).

Distarch phosphates with 0.4% to 0.5% phosphorus have beenprepared and they contain both slowly digested starch (SDS) andRS4 (Woo and others 1999). The modified starches were obtainedin quantitative yield, and provided 13% to 69% of SDS and 18%to 87% RS4. RS4 starches with low swelling power have also beenprepared similarly from wheat, corn, waxy corn, high amylosecorn, oat, rice tapioca, mung bean, banana, and potato starches.Phosphated di-starch phosphate, a modified RS made from highamylose maize starch, is currently used as food additive (E1413)in the EU.

Determination of RS

In vitro methodsThe main step of any method to measure the content of RS in

foods must first remove all of the digestible starch from the productusing thermostable �-amylases (McCleary and Rossiter 2004). Atpresent, the method of McCleary and Monaghan (2002) is consid-

ered the most reproducible and repeatable measurement of RS instarch and plant materials, but it has not been shown to analyze allRS as defined (Champ and others 2003). It is based on the principleof enzymic digestion and measures the portions of starch resistantto digestion at 37 °C that are typically not quantitated due to the ge-latization at 100 °C followed by digestion at 60 °C.

Two general methods specifically proposed to determine RS(Berry 1986; Englyst and others 1992) remove digestible starchusing different amylases, and the residual fraction is quantified af-ter solubilization in 2M KOH.

The Siljestrom and Asp (Siljestrom and Asp 1985) procedure in-cludes preparation and quantification of dietary fiber residue be-fore RS determination. This is usually done by drying the samplesat 105 °C. As heating influences the RS content in foods, resultsmay be modified by this step.

A modified method for measuring RS in dietary fiber residuesfrom various sources developed by Saura-Calixto and others(1993) involves mixing fiber residues with KOH, acetate buffer,and HCl. After incubation with amyloglucosidase samples arecentrifuged and diluted with distilled water. RS is calculated asglucose (mg) × 0.9. Advantages of the method are the use of smallamount of sample, less reagents and elimination of drying.

In vivo methodsDifferent methods are used to analyze RS in vivo.One of the ways to assay RS physiologically is to determine

starch in the undigested ileal content. Terminal ileal samples canbe recovered by intubation or from ileostomy bags. The classicway to substantiate starch digestion is by measuring the glycemicindex as described by Jenkins and others (1981). This impliesmeasuring the area under the curve (AUC) of the serum glucoseconcentration over the first 2 h after administering a starch and di-viding this by the serum glucose response after consumption ofan equal amount of glucose.

Determination of breath hydrogen (breath tests) can also beused as a semiquantitative measurement for RS. In a study on ef-fect of RS on human colon, increased fermentation was verifiedby elevated breath hydrogen excretion (Hylla and others 1998).From the different animal models, the antibiotic-treated rat modelis the one commonly used (Gudmand-Hoyer 1991).

Digestibility, energy value, and RDA of RSRS is highly resistant to mammalian enzymes. In cereal products,

the RS fraction is not digestible both in vitro and in vivo (Bornet1993). Four different RS fractions have been identified in cerealproducts: native starch, retrograded amylose, the amylo-lipid com-plex, and encapsulated gelatinized starch. After reaching the largeintestine, the RS fractions are fermented by the colonic flora, result-ing in short-chain fatty acids (SCFA). SCFA profiles derived from RSare lower in acetate and higher in butyrate than those of conven-tional fibers. The SCFA are an energy source for colonic cells (bu-tyrate) and to the body as a whole (acetate and propionate).

Maize starch acylated with acetic, propionic, or butyric anhy-dride are also RS and raise large bowel SCFA, apparently throughbacterial release of the esterified fatty acid and fermentation of theresidual starch (Annison and others 2003). Some sources of RSseem to be less available for fermentation, as has been observedin some chemically modified starches as well as RS in arepa (highcorn meal bread). Feeding trials on Himalaya 292, a hulless barleycultivar with a higher RS content, also have resulted in high levelsof SCFA in feces (Bird and others 2004).

Most studies indicate that 30% to 70% of RS is metabolized(Ranhotra and others 1991a; Behall and Howe 1995; Behall andHowe 1996; Cummings and others 1996; Ranhotra and others1996), while the balance is excreted in the feces. The variability is



largely due to effects caused by the malabsorption of the ingestedstarch. In human subjects, replacement of 27 g of digestible starchby RS (raw potato starch) in a single meal lowered diet-inducedthermogenesis by an average of 90 KJ/5 h (Heijnen and others1995). A study was designed to compare the metabolizable ener-gy of 2 starch sources, standard cornstarch and high amylosecornstarch (Behall and Howe 1996). Based on energy intake andfecal excretion from all subjects, the partial digestible energy valuefor the RS averaged 11.7 KJ/g RS, which was 67.3% of the energyof standard cornstarch. Control and hyperinsulinemic subjectsdiffered in their ability to digest RS, averaging 81.8% and 53.2%,respectively. RS averaged 2.8 kcal/g for all subjects but only 2.2kcal/g in the hyperinsulinemic subjects. This enables the use of RSin reducing the energy value of foods.

Approximately 20 g/d is recommended to obtain the beneficialhealth benefits of RS. However, worldwide, dietary intakes of RSare believed to vary considerably. It is estimated that intakes of RSin developing countries with high starch consumption rates rangefrom approximately 30 to 40 g/d (Baghurst and others 2001). Di-etary intakes in India and China were recently estimated at 10 and18 g/d (Platel and Shurpalekar 1994; Muir and others 1998). In-takes in the EU are believed to lie between 3 and 6 g/d (Dysslerand Hoffmann 1994). Dietary intakes of RS in the U.K. are estimat-ed at 2.76 g/d (Tomlin and Read 1990) and are believed to rangefrom 5 to 7 g/d in Australia (Baghurst and others 2001). In Swe-den, the daily RS intake is estimated to be 3.2 g (Liljeberg 2002).In New Zealand, RS intakes have been approximated to be 8.5 g/dand 5.2 g/d in 15- to 18-year-old males and females, respectively(Baghurst and others 1996).

Beneficial physiological effects of RSA number of physiological effects have been ascribed to RS

(Nugent 2005), which have been proved to be beneficial forhealth.

RS as a component of DFRS appears to be highly resistant to mammalian enzyme and

may be classified as a component of fiber on the basis of the re-cent definitions of dietary fiber given by AACC (2000) and NAS(2002). While part of the RS may consist of low-molecular-weightdextrins, the bulk consists of polymers, of which retrograded amy-lose often forms the major fraction (Ranhotra and others 1991a).Although not a cell wall component, RS is obviously nutritionallymore similar to NSP than to digestible starch. There is ample justi-fication that RS behaves physiologically like fiber. RS assays as in-soluble fiber, but has the physiological benefits of soluble fiber.Additionally, RS exhibits a level of slow digestibility and can beused as a vehicle for the slow release of glucose. Also, like solu-ble fiber, it has a positive impact on colonic health by increasingthe crypt cell production rate, or decreasing the colonic epithelialatrophy in comparison with no-fiber diets. There is indication thatRS like guar, a soluble fiber, influences tumorigenesis, and reduc-es serum cholesterol and triglycerides. Overall, since RS behavesphysiologically as a fiber, it should be retained in the TDF assay(Haralampu 2000).

Prevention of colonic cancerStarch unabsorbed in the small intestine is fermented by the mi-

croflora of the large intestine. Generally, starch is not present inthe feces of humans or experimental animals, indicating more orless complete fermentation. In vitro experiments with human fecalinocula have shown that the butyrate yield from starch is high. Asbutyrate is a main energy substrate for large intestinal epithelialcells and inhibits the malignant transformation of such cells in vit-ro; this makes easily fermentable RS fractions especially interest-

ing in preventing colonic cancer (Asp and Bjorck 1992).Significant changes in fecal pH and bulking as well as greater

production of SCFA in the cecum of rats fed RS preparations havebeen reported (Ferguson and others, 2000), which have beensuggested to resemble the effects of soluble dietary fiber. However,when RS was combined with an insoluble dietary fiber like wheatbran, much higher SCFA levels, in particular butyrate was ob-served in the feces (Leu and others 2002). In rats, when RS wascombined with psyllium, the site of RS fermentation was pushedmore distally. As the distal colon is the site where most tumorsarise it may be of additional benefit for cancer protection if fer-mentation is further enhanced within the distal colon (Morita andothers 1999).

Hypoglycaemic effectsFoods containing RS moderate the rate of digestion. The slow

digestion of RS has implications for its use in controlled glucoserelease applications. The metabolism of RS occurs 5 to 7 h afterconsumption, in contrast to normally cooked starch, which is di-gested almost immediately. Digestion over a 5- to 7-h period re-duces postprandial glycemia and insulinemia and has the poten-tial for increasing the period of satiety (Raben and others 1994;Reader and others 1997).

A study using 10 healthy normal-weight males fed test mealscontaining either 50 g starch free of RS (0% RS), or 50 g starchcontaining a high level of RS (54% RS) proved the ability of highRS meals to significantly lower the postprandial concentration ofblood glucose, insulin, and epinephrine (Raben and others1994). Similarly, from a human study (Reader and others 1997),using a commercial RS3 ingredient (CrystaLean®), the maximumblood glucose level was found to be significantly lower than thatof other carbohydrates (simple sugars, oligosaccharides, andcommon starch). The RS3-containing bar decreased postprandialblood glucose and may play a role in providing improved meta-bolic control in type II diabetes (non-insulin dependent).

As a prebioticRS has been suggested for use in probiotic compositions to

promote the growth of such beneficial microorganisms as Bifido-bacterium (Brown and others 1996). Since RS almost entirelypasses the small intestine, it can behave as a substrate for growthof the probiotic microorganisms.

Reduction of gall stone formationThe digestibility of starch in rice and wheat is increased by mill-

ing to flour (Heaton 1988). Digestible starch contributes gall stoneformation via a greater secretion of insulin and insulin in turnleads to the stimulation of cholesterol synthesis. RS is found to re-duce the incidence of gallstones (Malhotra 1968). Gallstones areless in South India where, whole grains are consumed rather thanas flour in Northern India. Notably, dietary intake of RS is 2- to 4-fold lower in the United States, Europe, and Australia, comparedwith populations consuming high-starch diets, such as India andChina, which may reflect in the difference in the number of gall-stone cases in these countries (Birkett and others 2000).

Hypocholesterolaemic effectsHypocholesterolemic effects of RS have been amply proved. In

rats, RS diets (25% raw potato) markedly raised the cecal size andthe cecal pool of short-chain fatty acids (SCFA), as well as SCFAabsorption and lowered plasma cholesterol and triglycerides.Also, there was a lower concentration of cholesterol in all lipopro-tein fractions, especially the HDL1 and a decreased concentrationof triglycerides in the triglyceride-rich lipoprotein fraction.

Results of feeding trials on rats using RS from Adzuki starch (AS)and tebou starch (TS) suggested that AS and TS had a serum cho-



lesterol-lowering function due to the enhanced levels of hepaticSR-B1 (scavenger receptor class B1) and cholesterol 7�-hydroxy-lase m RNA (Han and others 2003). The bean starches loweredthe levels of serum total cholesterol and VLDL + IDL + LDL cho-lesterol, increased caecal concentration of short-chain fatty acids(in particular butyric acid concentration), and increased faecalneutral sterol excretion.

From studies on hamsters fed diets containing cassava starchextrudated with 9.9% oat fiber or cassava starch extruded with9.7% RS, hypocholesterolemic properties of both were demon-strated suggesting their use in foods to improve cardiovascularhealth (Martinez and others 2004).

Inhibition of fat accumulationReplacement of 5.4% of total dietary carbohydrates with RS in a

meal could significantly increase postprandial lipid oxidation sug-gesting reduction in fat accumulation in the long term (Higginsand others 2004).

Absorption of mineralsA study to compare the intestinal apparent absorption of calci-

um, phosphorus, iron, and zinc in the presence of either resistantor digestible starch brought out that a meal containing 16.4% RSresulted in a greater apparent absorption of calcium and ironcompared with a completely digestible starch (Morais and others1996). Thus RS could have a positive effect on intestinal calciumand iron absorption.

Undesirable manifestations of RSSome undesirable manifestations of RS are also seen in clinical

studies (Reussner and others 1963). One of the most alarming in-fluences is the cecal enlargement, especially in rats. But, in hu-mans, it is said to be of little relevance because of the consider-ably smaller size and weight of cecum as well as its smaller role inthe human physiological function. Pelvic nephrocalcinosis is an-other phenomenon observed in rats especially those fed withmono substituted cross-linked starches and mono substitutedstarches (Baley and others 1973).

Applications of RSThe industrial applications of RS are mainly in the preparation

of moisture-free food products (Yue and Waring 1998). Bakeryproducts such as bread, muffins, and breakfast cereals can beprepared by using RS as a source of fiber. The amount of RS usedto replace flour depends on the particular starch being used, theapplication, the desired fiber level, and, in some cases, the de-sired structure-function claims. From a quality standpoint, someapplications are more sensitive to flour replacement than others.For example, bread and rolls, which generally have a bland flavor,are low-fat and require a minimum amount of gluten for structure;the maximum flour replacement is typically 10% to 20% withoutnoticeably changing the texture.

A type III enzyme-RS with a melting point of at least 140 °C,which could be used as a low-calorie flour replacer in bakeryproducts exhibits baking characteristics (cookie spread, goldenbrown color, pleasant aroma, surface cracking) comparable tothose achieved using conventional wheat flour (Haynes and oth-ers 2000).

Excellent quality sponge cakes have been prepared by replac-ing 30% of flour with 4 cycled autoclaved-cooled RS3 corn starch(RS3), cross-linked maize starch (RS4) and annealed and cross-linked RS4 maize starch (ARS4) while for yellow layer cake, the re-placement level was found to be at 12.5% (Po and others 1994;Myung-Hee-Kim and others 2001).

High amylose corn starch (HACS) coatings with RS at 20% to24% showed excellent properties useful for tablet coatings (Di-mantov and others 2004).

Hydrolyzed starches (those which retain their granular structureand essentially behave like unmodified starches in undergoinggelatinization on heating), which are also referred to as thin boil-ing starches, are also a form of RS. The advantage of this starch isthe high concentration, which can be used as a paste of low vis-cosity and its ability to set as a firm gel (Seib and Kyungsoo 1999).

Cross-linked starches based on maize, tapioca, potato of RS4type have been useful in formulations needing pulpy texture,smoothness, flowability, low pH storage, and high temperaturestorage (Sajilata and Singhal 2005).

Commercial sources of RSIn the commercial development of RS, it is advantageous to start

with a native starch high in amylose. Nearly all patented process-es are based on the propensity of high-amylose starch to retro-grade, or form highly crystalline regions, which are resistant to en-zymatic hydrolysis (Crosby 2001). High-amylose maize starcheshave high gelatinization temperatures, requiring temperatures thatare often not reached in conventional cooking practices (154 °Cto 171 °C) before the granules are completely disrupted. Thesestarches offer an opportunity to manipulate the amount of RSpresent in food products.

The first commercial RS was introduced as Hi-maize in Australiain 1993 by Starch Australasia, now part of Natl. Starch and Chem-ical Co. This product is a natural granular form of starch producedfrom a corn hybrid containing more than 80% amylose. Hi-maizeanalyses as 42% RS and has gained widespread use in Australiain breads and other baked goods.

Commercial sources of RS (Ranhotra and others 1996), such asCrystaLean® (Opta Food Ingredients, Inc., Bedford, Mass., U.S.A.),Novelose® (Natl. Starch and Chemical Co., Bridgewater, N.J.,U.S.A.) and Amylomaize VII (Cerestar Inc., Hammond, Ind.,U.S.A.) are now available to increase the DF content in foods andprovide other functional properties. CrystaLean ® is a commer-cial, highly retrograded RS3 based on the ae–VII hybrid. It is pro-duced by first fully hydrating and disrupting the starch granules,followed by an enzymatic debranching of the amylopectin toyield a low DE maltodextrin mixture, which is almost entirely astraight chain. Then, the mixture is treated through thermal cyclesto achieve a high level of retrogradation before drying. CrystaLe-an® containing 41% RS is digested slowly, at approximately halfthe rate of maltodextrin. The ingredient was introduced in the ear-ly 1990s and is now used in products for diabetics.

Shortly after the launch of CrystaLean, Natl. Starch introduced avery similar product named Novelose 330. More recently, Natl.Starch Chemical Co. has developed processes for manufacturinggranular forms of concentrated RS containing 47% to 60% RS byheating and cooling high-amylose corn starch under conditionsof carefully controlled moisture and temperature. These productsare marketed as Novelose 240 and 260. Novelose ® 240 is a ther-mally modified RS2 based on ae-VII hybrid of corn (Shi and Trzas-ko 1997). The modification renders the native granule more stableby holding the starch at elevated temperature (60 °C to 160 °C) inthe presence of limited water (10% to 80%). Novelose 260 con-tains 60% TDF, the highest level available in a RS. It can be formu-lated into a broad range of foods such as pasta, cereals, andsnack foods that can carry a rich-in-fiber labeling. Novelose 240(RS2), 260 (RS2), and 330 (RS3) have melting temperatures of99.7 °C, 114.4 °C, and 121.5 °C, respectively. These products of-fer medium/high, high, and very high process tolerance and aretherefore suitable for use in a variety of processed foods. Anotherplayer is Cerestar (a Cargill company), which has launched Ac-



tistar containing 58% RS, made by crystallizing hydrolyzed tapio-ca starch (maltodextrins).

High-amylose corn (amylomaize) is the generic name for cornthat has an amylose content higher than 50%. The endospermmutant amylose-extender (ae) increases the amylose content ofthe endosperm to about 60% in many dent backgrounds. Modi-fying factors alter the amylose contents as well as desirable agro-nomic characteristics of the grain. The amylose-extender gone ex-pression is characterized by a tarnished, translucent, sometimessemi-full kernel appearance. U.S. production of high-amylosecorn is forecasted at 50000 acres for 2001. 100% of this productis grown under contract in Indiana for Cerestar and Pioneer. High-amylose corn yields vary, depending upon location, but averageonly 65% to 75% of that of ordinary dents. Three types are pro-duced commercially: Class V (50% to 60% amylose) and Class VII(70% to 80% amylose), and Class IX (90% amylose).

C*ActiStar (Cerestar Food and Pharma Specialties) is made fromnative, partially hydrolyzed starch by generating microscopicstructures that are not hydrolyzed by digestive enzymes in thesmall intestine (58% RS). The specific structure of C*ActiStar favorsits fermentation to butyrate and helps to reach the lower parts ofthe large bowel, which is the most relevant segment of the colonfor the gut health maintenance. It can be used in a variety of food-stuffs such as bread, cereal bars, biscuits/cookies, muesli, low-fatfermented milk, UHT flavored milk drinks, and ready-to-use pow-dered mixes such as instant soups and instant chocolate. WithC*ActiStar, each serving can provide a significant amount of RS,which will contribute to an increase in the pre-existing daily in-take of RS. MGP Ingredients, Inc. (Atchison, Kans.) and Cargillhave announced a business alliance for the production and mar-keting of a new RS product called FibersymTM HA that is derivedfrom high-amylose corn and ideal for use in a wide array of lowernet carbohydrate food products. Delivering more than 70% di-etary fiber, it greatly reduces net carbohydrate levels in foods. Ap-plications cover a wide variety of products, including breads, tor-tillas, pizza crust, cookies, muffins, waffles, breakfast cereals,snack products, and nutritional bars. FibersymTM HA joins MGPI’sother resistant starches, which include a wheat-based RS, Fiber-symTM 70 and a potato-based variety, FibersymTM 80 ST.

Roquette (Roquette, Freres, France) recently developed NutrioseFB, a new dextrin that offers all the benefits of RS and, in addition, isa soluble fiber. Because it is only slightly digested in the small intes-tine and then slowly fermented in the colon, it fits the functionalpattern of RS with a low glycemic response. Fibersol-2, offeredthrough a joint venture of ADM and Matsutani, is a digestion-resis-tant maltodextrin. Resistant starches that test high in TDF such asRoquette’s Nutriose FB 06 at 85% fiber content or ADM/Matsutani’sFibersol-2 at 90% make it possible to enrich products with fiber tooptimum recommended levels and to support label claims.

Research is intensifying regarding RS4 starches created using di-functional phosphate reagents, available for inclusion in foods.However, as yet there is a lack of information regarding their poten-tial clinical and physiological effects (Brown 2004). As RS is includ-ed within the definitions of dietary fiber by the AACC (Anon 2000;Jones 2000), the Inst. of Medicine of the Natl. Academies (Inst. ofMedicine 2002), and is measured within the remit of the AOACmethod (Prosky and others 1985), which is used in the UnitedStates, U.K., Australia, and Japan, commercially manufacturedsources of RS can be used as vehicles to increase the total dietary fi-ber content of foods and food products without affecting taste andtexture (Liversey 1994). They may also be used to provide fiber insome commercially available low-carbohydrate foods marketed forthose following low-carbohydrate dieting regimens.

There are a number of advantages to using commercially manu-factured RS in food products. Unlike natural sources of RS (that is,legumes, potatoes, bananas), commercially manufactured RS are

not affected by processing and storage conditions. For example,the amount of RS2 in green bananas decreases with increasingripeness; however, a commercial form of RS2, Hi-maize, does notexperience these difficulties. Among the newest developments inresistant starches is an RS2 that remains resistant after mild foodprocessing (Novelose 240). Compared with conventional fibers, ithas many advantageous features. It is white and has a bland flavorand a fine particle size between 10 and 15 �m. It also has a re-duced caloric content and may be used as a bulking agent tocomplement reduced sugar or reduced-fat formulations. With aTDF content of approximately 40%, this RS2 can be used alone oras a functional complement to other fiber sources and can be la-beled simply as “cornstarch.” Most importantly, the commercialRS has a much lower water-holding capacity than do various tra-ditional fibers. Because it absorbs less water, adjustments in prod-uct formulations and processing are substantially minimized.

In general, RS has many properties, which outweigh the disad-vantages posed by it. Therefore, for deriving maximum benefitsfrom RS and minimizing undesirable effects of RS, it becomes es-sential to regulate the quantity of RS to be used.

Process tolerance needs to be considered when selecting andusing RS for a particular application (www.nstarch.com). The ma-jority of commercial RS on the market will retain their dietary fiberthrough typical baking processes and even mild extrusion. How-ever, extreme processing conditions may damage the RS, resultingin a loss of dietary fiber. Formulators should therefore analyze fin-ished foods made with processes involving extremely high tem-peratures, pressure, and/or shear to verify the level of dietary fiber.

RS is well-suited for low-moisture food systems where they canbe used at very high levels compared to traditional starches. Themajority of the commercially available RS rely on intact granules orcompact crystalline regions with high melting temperatures to resistdigestion. Therefore, these products generally will not swell or con-tribute viscosity during most processing. Essentially insoluble, RSwould not replace viscosifying starch in liquid applications.

ConclusionsRS has received much attention for both its potential health

benefits and functional properties. As a functional fiber, its fineparticles and bland taste make possible the formulation of a num-ber of food products with better consumer acceptability andgreater palatability than those made with traditional fibers. RSshows improved crispness and expansion in certain products andbetter mouthfeel, color, and flavor over products produced withsome traditional, insoluble fibers. It is ideal for use in RTE cereals,snacks, pasta/ noodles, baked goods, and fried foods and permitsfor easy labeling as simply starch, conferring additional nutraceu-tical benefits. Being nondigestible, RS can be used in reduced-fatand sugar formulations. RS has properties similar to fiber andshows promising physiological benefits in humans, which mayresult in disease prevention. Foods containing high levels of RSyield fewer calories and lower glycaemic loads—important formu-lation considerations for diabetics as well as the weight-con-scious. It is classified as a fiber component with partial or low fer-mentation. Technically, it is possible to increase the RS content infoods by modifying the processing conditions such as pH, heat-ing temperature and time, number of heating and cooling cycles,freezing, and drying. A number of commercially available RSpreparations would make it possible for a wide range of applica-tions with nutraceutical implications.

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Review- Resistant Starch