Starch || Tapioca/Cassava Starch

Starch: Chemistry and Technology, Third Edition Copyright © 2009, Elsevier Inc.ISBN: 978-0-12-746275-2 All rights reserved

Tapioca/Cassava Starch: Production and UseWilliam F. Breuninger1, Kuakoon Piyachomkwan2 and Klanarong Sriroth3

1National Starch and Chemical Company, Bridgewater, New Jersey, USA2National Center for Genetic Engineering and Biotechnology, Pathumthani,Thailand3Department of Biotechnology, Kasetsart University, Bangkok, Thailand

I. Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 541 II. Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545 III. Tapioca Starch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550 IV. Modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555 V. Food Applications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 556 VI. Industrial Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563 VII. Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564VIII. References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564

I. Background

Tapioca starch is obtained from the roots of the cassava plant, which is found in equa-torial regions between the Tropic of Cancer and the Tropic of Capricorn. Names for the cassava plant vary depending on the region: yucca (Central America), mandioca or manioca (Brazil), tapioca (India and Malaysia) and cassada or cassava (Africa and Southeast Asia). In North America and Europe, the name cassava is generally applied to the roots of the plant, whereas tapioca is the name given to starch and other proc-essed products. The plant belongs to the spurge family (Euphoriaceae). Previously, cassava was described as two edible species of the genus Manihot, Manihot ultissima Phol and Manihot palmata, based on the presence of high and low cyanide contents in roots (or called ‘bitter’ and ‘sweet’ cassava), respectively. Recently, both bitter and sweet cassava classes were classified as being the same species of Manihot esculenta.

Cassava is a shrubby perennial crop which is well-recognized for the ease of plan-tation and low input requirement. The plant can grow in all soil types, but root for-mation is better in loose-structured soils, such as light sandy loams and/or loamy

12

542 Tapioca/Cassava Starch: Production and Use

sands. It can grow even in infertile soil or acid soil (pH 4.4), but not in alkaline soil (pH 8). Cassava has excellent drought tolerance, so it can be planted in areas having less than 1000 mm/year of rain. Planting usually starts at the beginning of a rainy period. The plants are propagated readily by removing a piece of stem of 20 centimeters in length and having at least four nodules (called a stake) and placing it horizontally, vertically or inclined into the soil. Vertical planting is preferred as it gives higher root yields and better plant survival rates, and is easy for plant culti-vation and root harvest. To propagate effectively, good-quality stakes obtained from mature plants (9–12 months old) are planted vertically approximately 10 cm in depth below the soil surface and with all round spacing of 100 cm (10 000 plants/hectare). Less spacing (100 80 cm or 80 80 cm) is recommended for infertile sandy soil, whereas greater spacing (100 120 cm or 120 120 cm) is used in fertile soil. By vertical planting (or ‘standing’), the mature plants have at least two large branches (dichotomous branching) or three large branches (trichotomous branching). At matu-rity, which is reached in 8–18 months, plants may be 1–5 meters high, with feeder roots extending 1 meter into the soil. Storage roots of commercial interest are just below the soil surface, extending radially from the plant. The roots are typically har-vested on average at 10–12 months after planting. Too early or too late harvesting may result in lower root yields and root starch content. Optimal productivity of the plant for harvesting can be indicated by its harvest index, i.e. the ratio of root weight to total plant weight, which ranges from 0.5 to 0.7. Root harvesting can be accom-plished manually by cutting the stem at a height of 40–60 centimeters above the ground. Roots are then pulled from the ground using an iron or wooden tool with a fulcrum point in between the branches of the plant. Plant tops are cut into pieces for replanting, and roots are delivered to the processing factory.

Yields of cassava roots vary with variety, plant growth conditions such as soil, cli-mate, rainfall, and agronomic practices including fertilizer application, weed control, irrigation and multiple cropping.1 Although cassava cultivation requires only low input, the crop provides high yields if it is well-managed by planting with good-quality stakes at the optimal time, weed control during the first few months of planting, appli-cation of chemical fertilizers or manures, and root harvesting at the appropriate time and climate. Cassava is often grown on lands that are inadequate for higher value crops, and crops are seldom rotated. The farming practices in some major producing areas are such that plants are often short of nutrients. Fertilizer demand is, therefore, high and necessary for highest yield. Root yields are usually in the range 5–20 metric tons/acre (12–48 T/hectare).

Typical mature roots have different shapes (conical, conical-cylindrical, cylindri-cal, fusiform) and different sizes (3 to 15 centimeters in diameter), depending on variety, age and growth conditions. The color of the outer peel varies from white to dark brown. The cross-section of cassava roots shows the two major components which are the peel and the central pith (Figure 12.1). The peel is composed of the outer layer (called the periderm) and the inner layer (called the cortical region or cortex), which contains sclerenchyma, cortical parenchyma and phloem tissue. The large central pith of the roots is the starch-reserve flesh, comprised of cambium and parenchyma tissue and xylem vessels.

I. Background 543

Figure 12.1 (a) Cassava roots with conical, conical-cylindrical, cylindrical and fusiform shapes; (b) cross-section of cassava roots; and (c) drawing of root cross-section containing different components including (1) periderm or bark; (2) schlerenchyma; (3) cortical parenchyma; (4) phloem (1 to 4 peel); (5) cambium; (6) parenchyma (starch reserves); (7) xylem vessels; and (8) xylem bundles and fibers.


Table 12.1 Proximate analysis of cassava roots

Sourcea

1 2 3 4 5

Moisture (%, wet basis) 63.28 59.40 66.00 70.25 61.92Carbohydrate (%, wet basis) 29.73 38.10 26.00 26.58 35.7Protein (N 6.25,%, wet basis) 1.18 0.70 1.00 1.12 0.70Fat (%, wet basis) 0.08 0.20 0.30 0.41 0.10Ash (%, wet basis) 0.85 1.00 n.ab 0.54 0.92Crude fiber (%, wet basis) 0.99 0.60 1.00 1.11 0.68Potassium (mg/kg) 0.26 n.a. n.a n.a n.aPhosphorus (mg/kg) 0.04 400 n.a n.a n.aIron (mg/kg) n.a n.a n.a n.a n.aVitamin C (mg/kg) n.a 252 n.a n.a n.a

a1 reference 2; 2 reference 3; 3 reference 4; 4 reference 5; 5 experimental data of authors Sriroth and Piyachomkwanbn.a., not available

Typical mature roots have an average composition of 60–70% water, 30–35% car-bohydrate, 1–2% fat, 1–2% fiber and 1–2% protein, with trace quantities of vitamins and minerals (Table 12.1). Mature roots can range in starch content from as low as 15% to as high as 33%, depending on the climate and harvest time. Starch content reaches a maximum at the end of the rainy season. Less mature roots will be lower in starch content and higher in water, while overly mature roots will be lower in recov-erable starch content and have a woody texture, making starch processing difficult. Although cassava root is a poor source of protein, vitamins and minerals, it is a good energy source and is used as a staple food in many regions.

When cassava roots are to be used in the human diet or as animal feed, the toxicity of cassava is important. Cyanogenic glucosides are present in all parts of the cassava plant, including the edible roots. The two major types of cyanogenic glucosides, namely linamarin [2-(-D-glucopyranosyloxy)isobutyronitrile] and lotaustralin [methyl- linamarin or 2-(-D-glucopyranosyloxy) methylbutyronitrile] are synthesized from valine and isoleucine, respectively, and are found in cassava in an approximate ratio of 20:1.6 The toxicity of cassava-based products is due to the release of hydrogen cyanide from these cyanogenic glucosides.7 When plant tissues are damaged, intentionally or unintentionally, cyanogenic glucosides are hydrolyzed by linamarase, an endogenous, compartmentalized enzyme, to liberate glucose and acid-stable acetone cyanohydrin compounds.8 The cyanohydrin is further decomposed spontaneously under neutral and alkaline conditions (pH 5) or by enzymes to liberate volatile hydrogen cyanide or free cyanide.5,6 The content of hydrogen cyanide in cassava roots varies, depending on variety, harvest time, environmental conditions of growth and agronomic practices.11–13 The cyanide content is highly distributed in the peel portion (i.e. the periderm and cor-tex regions) rather than in the starchy parenchyma tissue (Table 12.2). Based on the cyanide contents in edible roots, cassava is classified into three classes: low toxic (or sweet) type; medium toxic type; and high toxic (or bitter) type, with cyanide contents

II. Processing 545

Table 12.2 Contents of total cyanogenic compounds in parenchyma tissue and peel of fresh cassava roots (harvested at 11 months after planting at the early and late rainy periods)

Varieties Total cyanide content (mg HCN/kg dry weight)a

Planting at early rainy period Planting at late rainy period

Parenchyma Peel Parenchyma Peel

Rayong 5 194 2160 338 3211Kasetsart 50 588 2447 671 3069Huay Bong 60 291 2100 311 3080KMUC 34-114-106 547 2360 477 4022KMUC 34-114-235 479 3862 231 2787KM99-1 204 2184 141 2215KM98-5 590 2213 875 2284KM140 245 2649 300 2643Rayong 7 229 2015 373 3257

aAs measured by an enzymic method according to reference 14

of 50, 50–100 and 100 mg HCN equivalent/kg fresh weight, respectively.15 Sweet cassava is preferred for direct consumption. The bitter type is mostly processed to industrial products such as chips and starch. During processing, a portion of the cya-nogenic compounds is removed, but some residues remain in finished products, the content depends on processing conditions. Proper processes such as cooking, boiling, drying, frying and fermentation are employed to effectively detoxify cassava and pro-duce products with a safe level of hydrogen cyanide.14,16,17

II. Processing

Roots are sold to processing factories, usually within 24 hours of harvest. Delays in reaching the processing facility can result in lower starch yield and increased micro-flora content. The latter can be observed as brown and black discolorations in a freshly broken root a few days after harvest. As a rule, roots delivered to starch factories are in areas where transportation distances (and costs) are low; this ensures raw material freshness. When arriving at the factory, roots are sampled and tested for starch content by specific gravity using a beam balance called a Rieman balance (Figure 12.2) which has been adopted from the potato starch industry.19 The analytical procedure is sim-ple: 5 kilograms of clean roots are weighed into a sample basket, then dumped into a second basket suspended in water and the specific gravity is determined to estimate the dry matter and starch content of the fresh roots. Rebalancing of the scale gives a direct reading as percentage of starch. Calibration of this method is required for cas-sava grown under different growth conditions.20 Shipman21 has provided an example of specific gravity data on which the direct reading balance is based. A good correla-tion of starch content in fresh cassava roots as determined by a simple beam balance and a specific enzymic method was found (Figure 12.2).22


y � 0.9886x � 0.1976 r � 0.920

0

10

20

30

40

0 10 20 30 40

Starch content by a beam balance (g/100 g fresh roots)

Sta

rch

cont

ent b

y en

zym

atic

met

hod

(g/1

00 g

fres

h ro

ots)

(a) (b)

Figure 12.2 (a) A beam balance or Rieman balance for determining cassava root starch content by specific gravity analysis; and (b) a correlation between starch contents of fresh cassava roots as determined by a beam balance and by the AACC enzymic method.18

The machinery of tapioca processing is highly varied. In both Thailand and Brazil there are well-equipped factories that utilize local, custom-built devices for processing roots, product streams, by-products and effluent. In addition, some manufacturers have successfully utilized equipment that is more common to potato and corn processing. The basic process of screening and density separation remains common to all machine varia-tions employed in the production of high-quality tapioca starch. Individual manufactur-ers have arrived at machines and configurations based on their own experiences, with raw material supply and finished product requirements influencing the selection process.

The basic process for isolating a high-quality tapioca starch is represented in Figure 12.3. At the factory, roots are transferred to a root hopper (Figure 12.4a) and are cleaned of dirt and sticks by a rotating slotted drum (Figure 12.4b). Cleaned roots are fed to a washer where recycled water is used (Figure 12.4b). In the early stage of the washer, stones sink in the water, while roots are lifted by the action of the washer paddles. The latter stages remove the peel from the roots. Roots are chopped into 1–2 centimeter chunks by a cutting blade and fed to a saw-tooth rasper for intense attri-tion into a pulpy slurry (Figure 12.4c). Liquid recycled from the process is fed along with chopped root into the rasper. Use of a decanter for fruit water separation, as applied in potato starch processing, is optional as the protein and other impurities of cassava are very low. Fresh rasped root slurry from the rasper is then pumped through a series of coarse and fine extractors, either vertical or horizontal (Figure 12.4d), where fiber is removed by screens arranged conically in continuous centrifugal perfo-rated baskets. Recently, an extractor equipped with curved screens was introduced to improve filtering efficiency. Starch slurry exiting the coarse extractor equipped with a filter cloth and a screen with an aperture of 150 microns (100 mesh) to 125 microns (120 mesh) still contains a large amount of fine fiber which must be removed in a fine extractor equipped with a finer screen (140–200 mesh). Starch slurry during transport

II. Processing 547

Waste water (2,323 / 30.38)Root washer

Peel (11.27 / 0.03)

(761.03 / 32.21)

Root chopper & rasper

Screener

Dewatering

Extractor 1

Separator Pulp press

Cassava pulp

Extractor 2

Flash dryer & packaging

Cassava root

Cassava starch

Vapour (82.62 / 0.40)

Starch Loss (3.36 / 0.0047)

(757.58 / 32.52)

(2,127.41 / 51.60)

(2,544.37 / 41.75)

(855.57 / 3.12)

(266.63 / 4.78)

(183.28 / 1.91)

(110.96 / 1.11)(284.15 / 0.68)

(198.17 / 0.28)

Water (403.71 / 0)Sulfur water (419.75 / 0)

Sulfur water (242.37 / 0)

Water (896.98 / 0)

Figure 12.3 Basic process for isolating a high-quality tapioca/cassava starch. The numbers in parenthesis represent the mass balance (tons/day) and cyanide balance (kg/day) of a factory with the production of capacity ~200 tons of tapioca/cassava starch per day. (Modified from Sriroth et al.23 and Piyachomkwan et al.24)

to each extraction stage is passed through a sand-removing hydrocyclone to ensure complete removal of sand. Extra filtration, such as a rotary brush strainer, is installed to ensure against passage of a starch clump. Pulp from the coarse extractor is repeat-edly re-extracted to achieve minimal loss of starch trapped in the moist pulp (60–70% moisture content and 45–55%, dry basis, starch content).25 Starch slurry received from the fine extraction has a concentration of 20–35% (10–17 ° Baume). The starch slurry is further concentrated to 40% (20 ° Baume) using a two-phase or three-phase separator (Figure 12.4e) or a series of hydrocyclones (Figure 12.4f). Starch may be recovered from the final starch stream and dried, or the stream may be used to supply a chemical modification process. To produce native starch, the concentrated starch slurry is dewatered in a horizontal centrifuge (Figure 12.4g) to produce starch cake with a moisture content of 35–40%. Alternative processes of dewatering, e.g. high-pressure filtration26 or use of a filter press, are used in some starch factories to reduce starch loss in the liquid stream. High-moisture starch cake is then subjected to a pneumatic conveying dryer, known as flash dryer, to lower the moisture content to 13% prior to packing (Figure 12.4h). Starch dust lost through the two cyclones can be recovered by being trapped with venturi scrubbers or filter bags.


Figure 12.4 Machinery of tapioca starch processing.

II. Processing 549

In the cassava starch process, the consumption of water and energy is critical, since it affects both production cost and starch quality. During the extraction process, the starch is purified by multiple stages of fiber screens and starch washers to remove solubles and finely divided fiber. Water utilization is optimized by reuse prior to dis-charge. Most commonly, water flow is countercurrent to the starch flow. All process water streams contain a small amount of sulfur dioxide for control of microbes and as an aid in processing. Modern factories also practice pretreatment of water, which consists of flocculation, chlorination and filtration, ahead of process consumption. The final water discharge from the process is treated on-site to meet environmental requirements prior to release to public channels. By-products are consumed in useful applications, so there is no waste from the process. Fiber is used in animal feed for-mulations. Peels and waste-treatment sludge are good compost for the original cas-sava growing land or other agricultural purposes.

Starch recovery, as presently practiced, depends on a continuous supply of fresh root. Hence, factories are located close to the root producing areas. In Brazil, the processing season can be as short as six months. In Thailand, continuous processing is possible, although some starch producers are known not to operate during part of the rainy season when the starch content of cassava root is low and operating eco-nomics are less favorable.

Some creative approaches to try to match the regular demand of a tapioca pro-duction process with the irregular supply of feedstock have been taken. Meuser et al.27 demonstrated that starch could be recovered from either cassava chips or pel-lets, although the starch is obtained at some sacrifice of quality. Nauta28 has pro-posed large silos for the storage of tapioca starch, similar to those used in the potato processing industry. At present, the primary supply of tapioca starch remains fresh roots.

The quality of tapioca starches produced can be affected by fresh root quality, as well as the production practices of each factory. Nevertheless, commercial tapioca starches always comply well with industrial specifications which differ to some extent, depending on the manufacturers and end users. General specifications of cas-sava starch are summarized in Table 12.3.

Table 12.3 General specification of native cassava starch

Attribute Specification

Moisture content (% maximum) 13Starch content (% minimum) 85Ash (% maximum) 0.2pH 5.0 to 7.0Whiteness (Kett scale, minimum) 90Viscosity Barbender unit, BU, minimum at 6% dry weight

concentration600

Sulfur dioxide content (ppm, maximum) 30Cyanide content nilAppearance White, no speck, fresh odor


III. Tapioca Starch

Swinkels29 collected published characterization data for tapioca starch and compared it to that for other starches of commercial significance (Table 12.4). Tapioca starch is differentiated from other starches by its low level of residual materials (fat, protein, ash), lower amylose content than for other amylose-containing starches, and high molecular weights of amylose and amylopectin. The small amount of phosphorus in tapioca starch is partially removable30 and, therefore, not bound as the phosphate ester as in potato starch. It is also common to find protein and lipid values of zero, as reported by Hicks.31 The very low protein and lipid content is an important factor which differentiates tapioca starch from the cereal starches.

Typically, cassava starch contains 17–20% amylose. Unlike corn (0–70% amy-lose content) and rice (0–40% amylose content), no significant variation of amy-lose content has been found in cassava starch. Similar to other starches, the amylose molecules of cassava starch are not completely unbranched as indicated by their beta-amylolysis limit, a value lower than that for corn, potato, rice and wheat starches. In addition, cassava amylose has a higher molecular weight than other starches (Table 12.5). The amylopectin structure of cassava starch is compared to that of other commercial starches in Table 12.6. Figure 12.5 demonstrates the chain length distribution in amylopectin fractionated from cassava starch. Each fraction can be classified in terms of its chain length (reported as degree of polymerization, DP) and position in amylopectin molecules. Cassava amylopectin consists mostly of short chains in Fraction III, which are A and B1 chains. A small portion of extra long chains (Fraction I, less than 1% by weight) have also been observed in cassava amylopectin.34 The variation in chain length distributions of amylopectin fractionated from different cassava cultivars seems to be less affected by genetics (Figure 12.5), which is in agreement with a previous report by Charoenkul et al.34

Microscopic examination of tapioca starch granules reveals smooth, spherical granules 4–35 m in diameter, commonly with one or more spherical truncations.

Table 12.4 Tapioca starch in comparison to some other commercial starches29

Source Granule diameter (m)

Average diameter (m)

Amylose content (%)

Amylosea average DP

Tga,b range (°C)

Phosphorus (%)

Ash (%) Protein (%)

Lipid (%)

Tapioca 4–35 15 17 3000 65–70 0.01 0.2 0.10 0.1Potato 5–100 27 21 3000 60–65 0.08 0.4 0.06 0.05Normal corn

2–30 10 28 800 75–80 0.02 0.1 0.35 0.7

Waxy corn

2–30 10 0 n.a.c 65–70 0.01 0.1 0.25 0.15

Wheat 1–45 bimodal 28 800 80–85 0.06 0.2 0.40 0.8

aNow known to be approximate valuesbGelatinization temperaturecnot applicable

Table 12.5 Properties of amylose from different botanical sources32

Property Chestnut Kuzu Corn Potato Rice Sweet potato

Tapioca Water chestnut

Wheat

Iodine binding capacity (g/100g)

19.9 20.0 20.0 20.5 20.0–21.1 20.2 20.0 20.2 19.9

[] at 22.5°C in M KOH (mL/g)

242 228 169 384 180–216 324 384 n.a.a n.a.

Beta-amylolysis limit (%)

86 76 84 80 73–84 73 75 95 82

Degree of polymerization by weight, DPw (range)

440–14900 480–12300 390–13100 840–21800 210–12900 840–19100 580–22400 160–8090 n.a.

Degree of polymerization by weight, DPw (mean)

4020 3220 2550 6360 2750–3320 5430 6680 4210 n.a

Degree of polymerization by number, DPn (mean)

1690 1540 960 4920 920–1110 4100 2660 800 1290

DPw/DPn 2.38 2.09 2.66 1.29 2.64–3.39 1.31 2.51 5.76 n.a.Chain length, CL 375 320 305 670 250–370 380 340 420 270Chain number 4.6 4.8 3.1 7.3 2.5–4.3 11 7.8 1.9 4.8Unbranched

amylose (mol%)66 47 52 69 30 58 89 73

Phosphorus (g/g) 10 10 n.a. 3 None 6 7 n.a. n.a.

an.a., not available

Table 12.6 Chain length distribution of components from amylopectin debranching33

Starch types Chain

A1 A2 B1 B2 B3 B4

Wheat Number-average DPa 10 15 24 49 84 110Weight-average DP 11 15 25 51 84 111Weight% 18.5 21.4 35.6 20.9 2.3 0.3Molar% 35.4 27.4 28.3 8.2 0.6 0.1

Waxy rice Number-average DPa 10 15 24 44 69 86Weight-average DP 11 16 24 46 69 87Weight% 20.2 26.2 27.2 21.9 3.9 0.5Molar% 36.9 32.0 20.7 9.1 1.1 0.1

Potato Number-average DPa 10 14 24 44 69 86Weight-average DP 10 14 24 46 69 87Weight% 6.2 18.5 33.7 29.5 11.6 0.5Molar% 15.0 31.8 35.2 14.5 3.4 0.1

Cassava Number-average DPa 10 13 21 48 74 90Weight-average DP 10 13 22 49 74 91Weight% 9.4 17.0 45.6 24.7 2.7 0.6Molar% 18.9 26.3 43.6 10.4 0.7 0.1

Sweet potato Number-average DPa 10 14 23 48 77 99Weight-average DP 10 14 24 50 78 100Weight% 9.4 17.0 45.6 24.7 2.7 0.6Molar% 15.9 37.2 34.3 11.2 1.3 0.1

aDP, degree of polymerization


Figure 12.5 Gel permeation profiles of Pseudomonas isoamylase debranched amylopectin fractionated from cassava starches of two varieties (Kasetsart 50 or KU50 and Ranyong 5 or R5). (Isoamylase-debranched amylopectin was fractionated by gel permeation chromatography on Toyopearl HW55S and Toyopearl HW50S columns (300 20 mm). Each fraction was divided according to the wavelength of maximum absorption (max) of the glucan–iodine complex: fraction I (Fr. I), max 620 nm; intermediate fraction (Int. Fr.), 620 nm max 600 nm; fraction II (Fr. II), 600 nm max 525 nm and fraction III (Fr. III), max 525 nm and the straight line represents the degree of polymerization (DPn from 2 to 85) of glucans.

The hilum is off-center, and there are usually noticeable fissures that cross the hilum. Using a light scattering technique, Finkelstein and Sarko35 found that the layers in tapioca starch granules could be as thin as 0.2 m and that a single granule could have at least 40 layers. By way of comparison, potato starch granules were found to have a much coarser organization of only a few structural layers that are several micrometers thick.

When heated in excess water, starch undergoes an irreversible structural transition. As a result, starch granules heated in excess water lose birefringence and crystal-linity. The granules then swell and absorb more water, resulting in changes in the rheological properties of the starch–water mixture. These phenomena are well-known as starch gelatinization and pasting. A comparison of the processes for cassava and other starches is given in Table 12.7. There is more resistance to gelatinization in tapioca starch than would be expected based on its amylose content (compared to that of potato starch). This small inconsistency is likely due to a tighter organization of the tapioca granule.

Allen et al.37 studied the gelatinization of tapioca starch by taking samples from a Brabender ViscoAmylograph. Water penetrates to the middle of the granule from the truncated end. At 50°C, well below the starch gelatinization temperature, there is

III. Tapioca Starch 553

Table 12.7 Gelatinization, pasting and paste properties of starches from different botanical origins36

Typea Gelatinizationb Retrogradationc

(%)Pasting and paste propertiesd

To (°C) Range (°C) Enthalpy (H, J/g)

Pasting temperature (°C)

Viscosity (RVU)

Peak Hot paste Final

A-type starchNormal maize 64.1 0.2 10.8 12.3 0.0 47.6 82.0 152 95 169Waxy maize 64.2 0.2 10.4 15.4 0.0 47.0 69.5 205 84 100du Waxy maize 66.1 0.5 14.4 15.6 0.2 71.2 75.7 109 77 99Normal rice 70.3 0.2 9.9 13.2 0.6 40.5 79.9 113 96 160Waxy rice 56.9 0.3 13.4 15.4 0.2 5.0 64.1 205 84 100Sweet rice 58.6 0.2 12.8 13.4 0.6 4.3 64.6 219 100 128Wheat 57.1 0.3 9.1 10.7 0.2 33.7 88.6 104 75 154Cattail millet 67.1 0.0 8.5 14.4 0.3 53.8 74.2 201 80 208Mung bean 60.0 0.4 11.5 11.4 0.5 58.9 73.8 186 161 363Chinese taro 67.3 0.1 12.5 15.0 0.5 32.0 73.1 171 88 161Cassava 64.3 0.1 10.1 14.7 0.7 25.3 67.6 173 61 107

B-type starchae Waxy maize 71.5 0.2 25.7 22.0 0.3 61.6 83.2 162 150 190Potato 58.2 0.1 9.5 15.8 1.2 43.4 63.5 702 165 231

C-type starchLotus root 60.6 0.0 10.5 13.5 0.1 43.2 67.4 307 84 138Green banana 68.6 0.2 7.5 17.2 0.1 47.7 74.0 250 194 272Water chestnut 58.7 0.5 24.1 13.6 0.5 47.9 74.3 61 16 27

aA, B and C types are classified based on the polymorphism of starch by x-ray diffraction patternsbStarch gelatinization parameters were obtained by a differential scanning calorimeter. Range of gelatinization is the difference between conclusion temperature and onset temperaturesc % retrogradation is the percentage of the enthalpy of the first run (i.e. native samples) and the second run (i.e. samples stored at 4°C for 7 days)dAs determined by a Rapid ViscoAnalyzer, using 8% (w/w, dsb) starch in water (28 g of total weight)

disruption in the center of the granule. As the temperature increases further, the gran-ule increases in diameter until, at the point of peak viscosity, outer layers of the gran-ule are disrupted. Continued heating beyond the occurrence of peak viscosity gives continued imbibing of water, with some of the starch dispersing into solution and some swollen granular fragments remaining. Cooling of a freshly-prepared tapioca starch paste produces an increase in viscosity, some loss of clarity (but the pastes are still clearer than those of cereal starches, except for the all-amylopectin, i.e. waxy, starches), and a cohesive body. A tapioca starch paste may slowly form a weak gel. These changes are due to reassociation of amylose molecules in the aqueous system. While this property of gelation (also called setback or retrogradation) is common to all native starches containing amylose (see Chapter 8), the property is less noticeable in tapioca starch because of a lower amylose content and higher molecular weight amy-lose than is found in other starches. At 17% amylose, there is sufficient functionality that, by modification, it is possible to enhance gelation and/or suppress cohesiveness.


Similar to other starches, the physicochemical properties of starches are affected by many factors. While gelatinization, pasting and gelation of starches are a function of their botanical sources, starch preparations from the same basic origin may vary in their properties. The effect of cultivars, growing seasons and root ages on cassava starch properties have been repeatedly reported.38–42 Figure 12.6 is an example of variation in gelatinization process of cassava starches with different cultivation practices. In addi-tion, cassava starch properties can be affected by processing conditions. As previously described, sulfur dioxide is often used in the cassava starch isolation process at the centrifugal or extraction stage to increase extraction efficiency and to improve product whiteness. However, sulfur dioxide residues in finished products alter starch properties by lowering paste viscosity and increasing the gelatinization temperature.23 The differ-ence in granule stability of cassava starch indicates existing variation in granule archi-tecture and can influence cassava starch uses, in particular, the modification process.

The low amylose, low lipid and low protein contents, combined with the high molecular weight of its amylose, make tapioca a unique native starch for direct use

(c) (d)

55.0°C

57.5°C

62.5°C

67.5°C

75.0°C

(a) (b)

Figure 12.6 Changes in granular structure of cassava starch extracted from roots: (a) planted during the rainy period and harvested at 6 months; (b) planted during the rainy period and harvested at 12 months; (c) planted during the dry period and harvested at 6 months; (d) planted during the dry period and harvested at 12 months, when observed by hot-stage microscopy at different temperatures.

IV. Modification 555

in food and industrial applications and an excellent starting material for modifica-tion into specialty products. This unique position of tapioca starch was recognized as early as 1944, when Kiesselbach43 reported on the progress of waxy corn breeding for replacement of tapioca starch. While both waxy maize and tapioca starches have competed in some applications, tapioca remains differentiated by its gel-forming ability and bland taste. Tapioca starch utilization in specialty applications has con-tinued to grow. In 1974, with a shortage of gum arabic, tapioca starch received new attention as a replacement for it.44 Tapioca starch consumption continues to increase, as new applications where its properties are of unique value are found.

IV. Modification

Starch modifications can be classified as physical modifications, chemical modifica-tions and genetic modifications.45 Physical modification of cassava starch involves application of shear force, blending and thermal treatment. A combination of thermal treatment and shear force has been widely used to produce many extruded products and snacks. Well-known physically modified cassava starch products are alpha starch or pregelatinized starch and heat–moisture treated starch.

Tapioca starches, both native and chemically modified, are easily converted into an ‘instant’ (pregelatinized) form, also known as cold-water-soluble starch. This physi-cal modification is brought about by pasting of the starch slurry (30–40% dry solids with or without some additives) and subsequent drying. The conventional means of preparation is the continuous feed of starch slurry onto a hot drum at 160–170°C.46 The starch is cooked and dried, then scraped from the drum in a single process and milled to desired particle size. Pregelatinized starches have also been prepared by spray drying. The gelatinization can be performed by a cooking system ahead of the spray dryer or by steam injection to the slurry ahead of atomization.

Heat–moisture treated starch, sometimes called Tao starch in Thailand, is prepared from cassava starch by heating moistened starch (50% moisture content) at various temperatures and times. Heat–moisture treatment provides a modified starch that pro-duces a less cohesive, shorter-textured paste with improved shear resistance and gel properties, as compared to the long, stringy, cohesive paste of native tapioca starch.

For chemical modification, tapioca starch is easily modified to all current com-mercial derivatives. There are no special precautions or equipment required beyond what already might be practiced for a particular derivative or reagent applied to other starches. Recovery of modified products is facilitated in conventional washing and drying equipment. The reader is referred to Wurzburg47 and Chapter 17 for details of starch modifications, all of which may be practiced with tapioca starch. In the prepa-ration and evaluation of some derivatives of tapioca starch, some of its unique char-acteristics have been revealed.

Tapioca starch granules have multiple layers and a tightly organized structure, as previously mentioned. Penetration of reagents might be more difficult than with other commercial starches. Patel et al.48 studied graft copolymers of polyacrylonitrile and granular starches (Chapter 19). Their work showed that grafting took place on


the surface of tapioca granules, while similar work with potato starch showed graft-ing within the granule. A study of the gel microstructure of a hydroxypropylated, crosslinked tapioca starch by Hood et al.49 suggested that crosslinking occurs only in the outer regions of the granule. Later work by Mercier et al.50 established that crosslinking with epichlorohydrin is also in the outer portion of the granule and located on the amylopectin molecules.

Franco et al.51 and Piyachomkwan et al.52 treated both corn and tapioca starches with -amylase and/or amyloglucosidase. Corn starch was found to be more susceptible to hydrolysis than tapioca starch, which is consistent with the results of Hood and Mercier,53 who studied molecular structures of both unmodified and modified tapioca starch and found that hydroxypropylation of tapioca starch took place only in the amorphous areas of the granule, and that parts of the amylopectin molecules were likely underivatized because of a more dense (crystalline packing) structure. However, the details of reagent penetration and derivatization sites within the granule are not fully understood, leaving considerable opportunities for future research. Evidence presented here is for the purpose of differentiating tapioca from the other commercial starches. From what is known, it can be concluded that tapioca starch granules are highly layered and have a tight organization. Both amylose and amylopectin may have higher molecular weights than found in other common starches. Tapioca starch is modifiable by common chemical and biochemical reactions, but the products are more heterogeneous than those of other modified starches.

Genetic modification of starches (see Chapters 3 and 4) has received attention, as it is a cost-effective tool for modifying starch structure and functionalities. Recently, genetic engineering of the cassava plant has been done by antisense inhibition of granule-bound starch synthase (GBSS), the enzyme responsible for the synthesis of amylose.54 This cassava genotype produces amylose-free starch (all-amylopectin or waxy starch) with improved paste clarity and stability, which is more desirable in many applications, so an environmentally unfriendly chemical process is no longer required for modification after starch extraction. This can be another significant driv-ing force to accelerate the growth of the cassava starch industry.

As a native starch, lipids and protein residuals are significantly lower than they are in many other commercial starches. These properties of tapioca starch have been uti-lized in many industries and further enhanced by means of physical and/or chemical modifications which give close control of its properties to fit the needs of customers in process and product applications. However, tapioca starch is regarded as a spe-cialty starch outside of its local production area.

V. Food Applications

The greatest diversity of uses of tapioca starch is in the food industry (see Chapter 20). As an ingredient in foods, native and modified tapioca starch has been widely uti-lized. Tapioca pearls (previously called sago pearls since they were made from sago [Metroxylon spp.] starch) are also familiar to many. The pearls formed in spherical shape are a mixture of gelatinized and ungelatinized starch produced by heat–moisture treatment. To produce tapioca pearls the starch is wetted to equilibrium of 50%

V. Food Applications 557

moisture content. The moist starch is disintegrated and formed into spherical parti-cles by continuous mechanical shaking. The particles are then subjected to dry heat processing or roasting at 250–300°C. The pearls are cooled before being subjected to another drying process at a lower temperature (50–80°C) to reduce the moisture content of finished products (Figure 12.7). When cooked, the pearls have unique

Figure 12.7 The process of making tapioca pearls.


product characteristics, i.e. they produce very transparent and chewy pastes, making them popular in many dishes.

Other food applications have generally made use of tapioca starch as a thick-ener and stabilizer, with special emphasis on its lack of flavor contribution to food systems, allowing full and immediate detection of the flavor of the food itself.55,56 Chemical modifications, in keeping with the broadly accepted limitations of the United States Food and Drug Administration,57 have resulted in highly specialized tapioca starch products that give added value and functionality to foods. Thailand, as one of the world’s leading manufacturers and exporters of cassava-based modi-fied starches, also has regulations for chemically modified starches approved for food applications (Table 12.8).

Wood59 reports that, of the seven most common food allergies, two are associated with significant sources of food starch, namely, wheat and corn. Some food processors, sensitive to consumer perceptions of labeling, have sought to reformulate using tapioca starch or to specify tapioca starch in the development of new products that address the concern of allergic reactions.

Tapioca starch has long been the starch of choice in baby food for its physical properties of texture and stability, as well as its low flavor contribution. The starch used may be modified in order to survive the rigors of processing and enhance the physical properties of the final product. Starches containing amylose were found by Wurzburg and Kruger60 to take on some of the physical characteristics of modified starches when heated under certain conditions with salts and moisture. Smalligan et al.61 used steam injection as the heat and moisture source to prepare a tapioca starch for baby food having the enhanced properties of modified tapioca starch, but without modification. It is the opinion of the authors that, in the drive toward physical modifi-cations matching the properties of chemical modifications, tapioca starch will have an advantage in taste, molecular weight and non-starch residuals over cereal starches.

Tapioca starch is used broadly in the manufacture of Asian-style noodles in combi-nation with other ingredients. Kasemsuwan et al.62 used tapioca starch as an extender in mung bean noodles. The use of tapioca starch was based on paste clarity; the tex-tural properties imparted by the starch were adjusted by crosslinking. The resulting noodle was acceptable, with improved economics. Ishigaki et al.63 included tapi-oca starch in noodle dough of durum semolina in order to obtain an instant cooking noodle, instant cooking also being aided by grooving from the extruder die to aid in water uptake. Starches from other tuber and grain sources, substituted in the inven-tion, did not give noodles of acceptable texture and mouthfeel compared to those from tapioca starch. In this application, tapioca starch moderates water uptake dur-ing noodle rehydration. Starches of higher amylose content have the disadvantage of more difficult rehydration, due to retrogradation in the noodle.

Dextrinization of tapioca starch is well-known. The difficulty in dextrinizing corn starch,64 and the relative ease of tapioca starch conversion,65 have been described. The near-absence of lipids, which interfere with the dextrinization process, has given tapioca dextrins an advantage in stability and color because of their ease of manu-facture and control. However, the economics of base starch supply have resulted in a significant shift to waxy corn starch as a base for industrial dextrins, even though

V. Food A

pplications 559

Table 12.8 Specification of chemically modified starch for food applications according to Thai regulations

ndard/specification

2.0 to 9.0

3.0 to 7.0

5.0 to 7.5rboxyl group increase 0.1%

fur dioxide 50 mg/ka

chloritenganese 50 mg/kgrboxyl groups 1.1%osphate (reported as phosphorus) 0.04%

tenylsuccinate groups 0.03%pylene chlorohydrin 1 mg/kg ydroxypropyl groups 7.0%tyl groups 2.5%

osphate (reported as phosphorus) 0.4%

pylene chlorohydrin 1 mg/kg (or 5 mg/ge) Hydroxypropyl groups 4.0%tyl groups 2.5% and adipate groups 0.135%

tyl groups 2.5% and phosphate reported as phosphorus) 0.04%

tives in the context of the

Type of modified starch INS-numbera E-numberb Chemical reagentsc Sta

Pregelatinized starch – –Dextrind 1400 Hydrochloric acid 0.15% or orthophosphoric

acid 0.17%pH

Thin-boiling starchd 1401 Hydrochloric acid or orthophosphoric acid 7.0% or sulfuric acid 2.0%

pH

Alkali-treated starchd 1402 Sodium hydroxide or potassium hydroxide 1.0% pHBleached starchd 1403 Hydrogen peroxide and/or peracetic acid with

active oxygen 0.45Ca

Ammonium persulfate 0.075% and sulfur dioxide 0.05%

Sul

Sodium chlorite 0.5% NoPotassium permanganate 0.2% Ma

Oxidized starch 1404 E1404 Chlorine (as sodium hypochlorite) 5.5% CaDistarch phosphate 1412 E1412 Sodium trimetaphosphate Ph

Phosphorus oxychloride 0.1%Starch octenylsuccinate 1450 E1450 Octenylsuccinic anhydride 3% OcHydroxypropylated starch 1440 E1440 Propylene oxide 10% (or 25%e) Pro

HAcetylated starch 1420 E1420 Acetic anhydride Ace

Vinyl acetate 7.5%Adipic anhydride and acetic anhydride 0.12%

Monostarch phosphate 1410 E1410 Orthophosphoric acid or sodium or potassium orthophosphate or sodium tripolyphosphate

Ph

Hydroxypropyl distarch phosphate

1442 E1442 Sodium trimetaphosphate or phosphorus oxychloride and propylene oxide 10%

Prok

Acetylated distarch adipate 1422 E1422 Acetic anhydride and adipic anhydride 0.12% Ace

Acetylated distarch phosphate 1414 E1414 Phosphorus oxychloride followed by acetic anhydride 10% (or 8%e or vinyl acetate 7.5%e)

Ace(

aCCFAC International Numbering System (INS) 1989 ftp://ftp.fao.org/codex/standard/volume1a/en/CXxot04e.pdfbModified starches, Annex 1 of EEC Directive No. 95/2/EC (an ingredient category)cAccording to Thai Industrial Standard Institute (TISI) unless specified by others58

d Dextrin, bleached starch, starches modified by acid, alkali and enzyme or by physical treatment are not considered as food addiEEC Directive 95/2/EC

eAccording to US Food and Drug Administration (FDA) 21 CFR Chapter 157


production of tapioca food dextrins has experienced growth. Continued growth of tapioca starch dextrins is related to new uses, the properties of which cannot be matched by cereal starch dextrins. Tapioca starch dextrins have a long-established use as a high solids coating former in pan coating of confections. With current con-sumer interests in low-fat and no-fat foods, there has been a renewed interest in some old products. Tapioca starch dextrins have enabled food producers to develop low- or no-fat products having the taste, mouthfeel and texture expected by the consumer in the original food product. Current dextrin use for low- and no-fat products includes meats, sauces, soups, confections, baked goods and dairy products.66,67

Tapioca starch and chemically modified tapioca starches are easily converted to ‘instant’ (pregelatinized) forms (also known as cold-water-soluble starch). This phys-ical modification is brought about by pasting of the starch and subsequent drying as described in Section 12.4. Control of particle size is critical to texture and rehy-dration rate when the product is redispersed in water.68 Fine particle size results in a smooth texture on redispersion, e.g. in pudding preparation.69 As a comparison, coarse texture could be more desirable in fruit- or vegetable-based foods.

Pudding products have been prepared in the form of cook-up, instant and frozen types, using tapioca starch in a wide variety of chemical and physical modifications. Tapioca starch is favored in such applications because of lack of flavor contribution and fast meltaway, allowing the flavors of the pudding to be released.55 The water-binding capacity of gelatinized tapioca starch is good. Contributing to this prop-erty is its low amylose content and a good degree of dispersion on gelatinization. Hydroxypropylation increases its water-binding capacity and improves its ability to withstand freeze–thaw cycling. Hydroxypropylation also aids in redispersion if the starch is in a pregelatinized form. Control of dispersion on initial cooking has also been utilized.69 Acetylated tapioca starch is also a functional pudding starch.70 One of the more creative inventions utilizing the unique properties of tapioca starch is that of Glicksman et al.,71 who used unmodified tapioca starch, along with fat and emul-sifier, to produce a freeze–thaw stable pudding. When other unmodified commercial starches were used in the same formulation, syneresis (water separation) occurred. This invention made use of the formation of complexes between amylose molecules and fats, moderating both gelatinization and retrogradation.

Formation of complexes between tapioca amylose and lipids was studied in detail by Mercier et al.50 who found that, as the chain length of the fatty acid or monoglyc-eride increased, complexing observed by x-ray crystallography, iodine absorbance and solubility also increased. Complexes were only possible when the lipid employed was capable of fitting inside the amylose helix. Diglycerides and triglycerides did not form complexes. However, such complexing is not unique to tapioca amylose. It does, however, give the user of tapioca starch a more complete understanding of interactions in a processed food system where the previously mentioned unique prop-erties of tapioca are utilized.

Tapioca starch has a demonstrated ability to contribute to puffing or popping when heated in a microwave oven. Shachat and Raphael72 prepared a puffable snack prod-uct in which a flour-free dough, containing tapioca starch and other ingredients, gave puffed, crisp pieces on microwaving. The use of tapioca starch is described as ‘critical

V. Food Applications 561

to the invention.’ Birch and Goddard73 prepared an expandable snack product with tapioca starch by sealing a tapioca starch containing core dough with an outer dough not containing tapioca starch, to produce a coated product that pops on microwav-ing. Exactly how the popping takes place is not explained in either invention. Both inventions require some, if not all, of the tapioca starch granules to be ungelatinized. A later study of tapioca extrusion ahead of cooking expansion was done by Seibel and Hu,74 who found that die temperature and residence time were the primary influ-encing factors. A barrel temperature of 70–80°C was critical for a puffable cracker preparation which, under the conditions studied, did not fully gelatinize the tapioca starch. The puffing effect was thought to come from microcells of air in the extru-date. This leaves the probability that the presence of granular tapioca starch could simply be an indication of correct conditions to produce a puffable snack.

Sour cassava starch (known as Polvilho azedo in Brazil and Almidon agrio in Colombia), a naturally 30-day fermented and sun-dried starch, is used extensively to prepare snacks and biscuits. The unique characteristics of products made from this modified cassava starch are high specific volumes, baking expansion and crispness, i.e. it produces products with characteristics similar to those of extruded snacks.75 The improved rheological properties are believed to be an effect of degradative oxi-dation by organic acid and ultraviolet (UV) irradiation, and can be observed only in the baking of acidified-irradiated cassava starch, but not corn starch.76,77 Further investigation demonstrates that certain UV wavelengths, i.e. the short wavelengths of UVB and UVC, are essential for improving baking expansion of acidified cassava starch dough.78

Combined use of natural gums and starch, including tapioca starch, has been widely practiced in the food industry. Exact reasons for the synergistic effects that have been observed and reported are not fully understood at this time. While tapioca starch has been widely used in combination with gums in food systems, it does not likely contribute unique properties to the system beyond the properties already pre-sented. Fujii79 reported on the inhibition of hydroxypropylated tapioca starch pasting by low-methoxyl pectin. He also demonstrated that the combination of gelatin and tapioca starch can have variable results, depending on concentration. Kleemann80 reported variability of viscosity based on the molecular weight of gelatin used, with high molecular weight gelatin being more effective and higher concentrations of gelatin increasing the observed viscosity change. Kuhn et al.81 demonstrated an interaction between starch and xanthan under conditions of extrusion. Bahnassey and Breene82 suggest that the interaction of starch and gum could be as simple as a competition for water in the use system. Furthermore, the electrostatic interac-tion between positively or negatively charged chemical groups introduced to tapioca starch and gum can occur and significantly change its gelatinization temperature and rheological behavior.83,84 The properties of the starch can also be markedly altered by the addition of other ingredients. The effects of sucrose and sodium chloride, widely-used as ingredients in a variety of processed foods, on starch properties have been widely reported.85–90 Like other starches, the addition of sucrose and sodium chloride shifts gelatinization of tapioca starch to higher temperatures, but does not affect the gelatinization enthalpy. The effect of salt on gelatinizing tapioca starch is, however,


concentration-dependent. Salt tends to retard retrogradation of tapioca starch gels, whereas sucrose either has no effect or increases retrogradation of aged gels, depend-ing on the aging temperature.91 As evidenced by light microscopy, the addition of sucrose and sodium chloride have similar effects on cooking behaviors of various chemically modified tapioca starches used in food products (Figure 12.8). Increasing the gelatinization temperatures of starches in aqueous systems by sucrose is consid-ered to be due to an antiplasticizing effect92 and competition for available water,93 whereas the ionic nature of salts presumably causes an alteration in the weakly- anionic hydroxyl groups of starch molecules,94,95 as well as altering water structure.96 Recently, confocal laser scanning microscopy has been used to reveal the pres-ence of granule-associated protein in various starches,97,98 including tapioca starch. The protein-containing envelope of tapioca starch can be modified by ionic salts (Ca2), resulting in modification of its granular structure, as well as its hydration properties.99 Some additives such as glycerol, the most commonly used plasticizer, when blended with tapioca starch, increase the molecular mobility of glucan chains, thereby providing improved starch functionalities for promising production of biopol-ymer-based edible film.100–102

The effects of food ingredients on thermal transitions and physicochemical proper-ties are of importance to the processing and properties of starch-based products, and can play major roles in the quality and storage stability of tapioca starch-containing products. For the food scientist, it remains vital to understand the role of ingredients and their properties, with the understanding that results can vary with the conditions of use.

Water With sucrose With sodium chlorideTypes of starch

Uncooked Cooked Uncooked Cooked Uncooked Cooked

Native cassava starch

Hydroxypropylated cassava starch

Crosslinked cassava starch

Acetylated cassava starch

Cassava starch phosphate monoester

Figure 12.8 Hot-stage microscope pictures of uncooked (at 30°C) and cooked (at 70°C) native and various chemically modified tapioca starches in water containing sucrose (20% by weight) and sodium chloride (5% by weight), indicating different ease of cooking as a result of food ingredients.

VI. Industrial Applications 563

VI. Industrial Applications

Tapioca starch consumption in industrial applications has been more related to eco-nomics than to any unique functionality. While some performance characteristics of tapioca starch are advantageous in several applications, it is generally used in non-food applications close to the supply points, such as in Brazil, India and Southeast Asia. Non-food consumption of starch in North America and Europe is primarily from readily available sources in these areas, i.e. corn, wheat and potatoes.

Paper manufacturing is a significant consumer of starch, in both modified and unmodi-fied forms (see Chapter 18). The role of starch is to bind fibers, retain additives and increase strength. Further, if the granules are not fully dispersed, strength gains are con-siderable, while the drainage rate on the forming wire is not impeded.103 Chen104 studied the role of amylose, amylopectin and tapioca starch in papermaking and the retention of titanium dioxide pigment. Protective colloid effects were present with all three additives, but as the molecular weight of amylose increased, titanium dioxide retention increased, demonstrating that protective colloid effects were overcome. Even though unmodified starch can perform well in papermaking, the process is enhanced by functional modi-fication of the starch. Addition of positively charged chemical groups, usually tertiary or quaternary amines, establishes ionic binding with negatively charged cellulose fibers and pigment in the paper. Tapioca starch is suitable for such modifications. Additionally, modified tapioca starches and derivatives have been used in sizing and coating prepara-tions. In corrugating, unmodified tapioca starch has demonstrated technical advantage over corn starch as the adhesive (ungelatinized) portion of the corrugating formulation. Leake105 showed improvement in tack and green bond strength that could be translated to increased machine speed by virtue of the higher water-holding capacity when tapi-oca starch was used, compared to conventional formulations. It has also been possible to control uniformity and speed of gelatinization if the adhesive portion of the corrugating formulation is esterified tapioca starch.106 Tapioca starch has also been used as the car-rier portion of corrugating formulations by partial swelling with alkali, terminated by the addition of acid.107 The carrier portion of the formulation may also be tapioca starch, as demonstrated by Sakakibara and Iwase.108 Low-amylose starches, when cooked, provide viscous pastes with a cohesive texture and a low tendency to retrograde, which is pref-erable for use as adhesives. In addition, cassava starch is odorless and tasteless and its dried film can reabsorb water rapidly. It is, therefore, an excellent, remoistenable adhe-sive for use on postage stamps, envelope flaps, labels and gummed tape.

The textile industry is another significant user of starch for sizing, finishing and printing purposes. Starch, typically as a modified form, is primarily used as a warp size to increase yarn strength and abrasion resistance during the weaving process. Properties required include the formation of strong films to provide a protective coat-ing (partly on the surface and partly inside the yarn), good affinity to the yarn, good film flexibility, stable viscosity during application and ease of size removal. Modified tapioca starch possesses desirable functionalities for this application.

A large volume of tapioca starch is also used to make sweeteners and related products. This application primarily involves enzyme-catalyzed hydrolysis. Similar


to chemically modified starches, diverse products are produced by varying enzyme types, degree of starch hydrolysis and derivatization. Important products obtained by direct hydrolysis of starch are sugar syrups (glucose syrups and maltose syrups made using -amylase plus glucoamylase or -amylase, respectively, with dextrose equiva-lence (DE) values of 20) (see Chapters 7 and 21), maltodextrins (DE 20) and cyclodextrins (see Chapter 22). The advantages of using tapioca starch over the cereal starches for syrup production are the bland taste, clean flavor, high purity and ease of cooking due to a lower gelatinization temperature. Furthermore, many derivatives can be made from starch hydrolysis products by chemical or bioprocesses. The reduction of sugars and starch hydrolyzates, readily accomplished by hydrogenation, changes the carbonyl group to an additional hydroxyl group. These products called sugar alcohols (such as sorbitol, mannitol, maltitol and hydrogenated starch hydrolyzates) are reduced-calorie sweeteners that are useful in many food and clinical applica-tions. Fructose is produced from glucose by isomerization with glucose isomerase (see Chapter 21). Fermentation of starch hydrolyzates with different microorganisms provides a wide range of chemicals, such as monosodium glutamate (MSG), lysine, organic acids and alcohol. Advances in biotechnology and environmental concerns are the major driving forces that accelerate starch demand for the production of eco-friendly chemicals. The demand for cassava starch for this purpose, especially for the production of bioethanol, has also increased.

VII. Outlook

There are bright prospects for continued growth of the cassava starch industry. The low residuals in the starch and favorable flavor properties are being widely used in the food industry with opportunities for growth as the consuming public shifts toward lower-fat foods, reduced dependence on chemical modifications and avoid-ance of cereal starches, without sacrifice of eating quality. Breeding holds promise of both increased and decreased amylose contents. Properties of these starches can be further modified physically and/or chemically. Root production will improve as yield and maturity factors are made a part of hybrid selection, and with improvements in crop and soil management techniques.

VIII. References

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