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Some perspectives on the use of cheese as a foodingredientJohn A. Lucey
To cite this version:John A. Lucey. Some perspectives on the use of cheese as a food ingredient. Dairy Science & Tech-nology, EDP sciences/Springer, 2008, 88 (4-5), pp.573-594. <hal-00895795>
Dairy Sci. Technol. 88 (2008) 573–594 Available online at:c© INRA, EDP Sciences, 2008 www.dairy-journal.orgDOI: 10.1051/dst:2008010
Review
Some perspectives on the use of cheeseas a food ingredient
John A. Lucey*
Department of Food Science, University of Wisconsin-Madison,1605 Linden Drive, Madison, WI 53706, USA
Abstract – Over the past few decades, cheese has been growing in commercial importance in thefood industry because of its use as an ingredient, including as a topping on pizza, filling in ap-petizers, slices on hamburgers, and sauces in pasta dishes. Traditionally, cheeses like Mozzarella,cheese powders, processed and imitation cheeses were the main ingredient cheeses but now thereare a growing number of other cheese types being used as ingredients, e.g. in the US these includepizza type (i.e. cheese not meeting the standard of identity for Mozzarella), Hispanic and creamcheeses. For ingredient cheeses, such as Mozzarella, considerable research has been conducted onthe impact of altering milk composition, manufacturing conditions and the type of starter cultureson the functional properties that are important for its use as an ingredient, e.g. slicing, shreddingand melting properties. It is now recognized that insoluble calcium associated with the caseins incheese plays a critical role in cheese texture, including melting properties. The total and insolu-ble calcium contents can be controlled by altering the critical pH values during manufacture, e.g.at coagulation or whey draining. Post-manufacture changes in the proportions of insoluble/solublecalcium are primarily responsible for most of the early changes in cheese texture and not proteolysisas was commonly believed until recently. End-users of cheese in various foods routinely demandconsistent functionality over a long shelf-life and the cheese has to meet very specific performancetargets, e.g. color and flow. Various approaches to modify the insoluble calcium content in cheese,studies on the performance of cream cheese as an ingredient and strategies to extend the acceptableperformance window for cheese are described. A framework is presented that allows cheese textureand functional properties to be described in terms of specific molecular interactions of the caseins.
functionality / insoluble calcium / rheology / texture
摘摘摘要要要 – 干干干酪酪酪作作作为为为食食食品品品配配配料料料的的的前前前景景景。。。在过去几十年里, 干酪作为食品配料的使用量逐年增加, 干酪主要用做比萨饼、开胃食品、意大利面条的调味料、汉堡包等的配料。过去,Mozzarella 干酪、干酪粉、再制干酪和模拟干酪主要用作食品的配料,但是现在,许多其他类型的干酪也用做食品配料,如在美国广泛使用的 Pizza型干酪 (这类干酪不执行Mozzarella干酪的标准)、西班牙干酪和奶油干酪。在这些干酪中, Mozzarella 干酪最具有代表性。关于通过调整原料奶组成、改变加工条件和不同类型发酵剂对Mozzarella干酪功能性影响的报道非常多,而干酪的特性,如切片性、破碎性和融化性等对加工食品的品质具有重要的影响。研究证明,干酪中与酪蛋白结合的不溶性钙含量影响干酪的质构和融化性。通过改变加工过程中 (如凝乳或排乳清)的 pH可以控制总的和不溶性钙的含量。在加工后期不溶性/可溶性钙比例的变化是导致干酪质构变化和蛋白不水解的主要原因。干酪在各种食品中使用后的终端产品必须要考虑在货架期内干酪的功能性,而且,所用的干酪必须满足特定的要求,如颜色和流动性。在干酪的研究中,采用不同的方法来调整干酪中不溶性钙的含量,如研究改善奶油干酪性能使其适用于食品配料。新近的研究观点认为,特定酪蛋白分子之间相互作用决定了干酪的质构和功能性。
功功功能能能性性性 /不不不溶溶溶性性性钙钙钙 /流流流变变变性性性 /质质质构构构
* Corresponding author (通讯作者): [email protected]
Article published by EDP Sciences
574 J.A. Lucey
Résumé – Quelques perspectives sur l’utilisation du fromage en tant qu’ingrédient alimen-taire. Au cours des dernières décennies, le fromage a pris une importance commerciale crois-sante dans l’industrie alimentaire du fait de son utilisation comme ingrédient, tel que garnituresur pizza ou dans les produits apéritifs, tranches sur hamburgers et sauces dans les plats de pâtes.Les fromages comme la Mozzarella, les poudres de fromages, les fromages fondus ou imitationsont été traditionnellement les principaux fromages ingrédients. Actuellement, un nombre croissantd’autres types de fromage sont utilisés comme ingrédients, comme par exemple aux États-Unis,les fromages de type pizza (c’est-à-dire des fromages non conformes aux normes pour l’appella-tion Mozzarella), des fromages hispaniques ou des Cream-cheeses. Pour les fromages ingrédientstels que la Mozzarella, une recherche considérable a été faite sur l’impact des modifications de lacomposition du lait, des conditions de fabrication et du type de levain sur les propriétés fonction-nelles importantes pour leur utilisation comme ingrédient, par exemple l’aptitude au tranchage, aubroyage et à la fonte. Il est maintenant reconnu que le calcium insoluble associé aux caséines dansle fromage joue un rôle critique dans la texture du fromage et ses propriétés de fonte. Les teneurs encalcium total et insoluble peuvent être contrôlées en modifiant les valeurs de pH critique au coursde la fabrication, par exemple lors de la coagulation et de l’égouttage du lactosérum. Après la fabri-cation, ce sont les changements dans les proportions de calcium insoluble/calcium soluble qui sontprincipalement responsables de la plupart des premiers changements dans la texture du fromage, etnon pas la protéolyse comme on le croyait jusqu’à récemment. Pour plusieurs applications, l’utili-sateur final de fromage exige systématiquement des fonctionnalités constantes sur une longue duréede vie et le fromage doit répondre à des objectifs de performance très spécifiques, par exemple lacouleur et l’écoulement. Différentes approches pour modifier la teneur en calcium insoluble dansle fromage, des études sur les performances du Cream-cheese comme ingrédient et les stratégiespour élargir la plage des performances acceptables du fromage sont décrites. Les grandes lignespermettant la description de la texture et des propriétés fonctionnelles des fromages sont présentéessous l’angle des interactions moléculaires spécifiques des caséines.
propriété fonctionnelle / calcium insoluble / rhéologie / texture
1. INTRODUCTION
Cheese is an extremely versatile foodproduct that has a wide range of textures,flavors and end-uses. The texture and bodyof cheese varieties can range from soft tofirm, smooth/creamy to curdy, brittle tolong, mechanically open to closed, or fromcheese with splits to round eyes. The phys-ical properties of cheese are largely de-termined by the casein content, the type,number and strength of casein interac-tions, cheese composition and ripening re-actions [35, 53]. There have been severalrecent reviews on cheese texture and func-tionality [18, 19, 27, 53]. Cheese has beenused as an ingredient in various foods sincethe first recorded consumption of cheese it-self, mainly to add flavor to bland foods.Nowadays, cheese is being used increas-ingly as an ingredient in a wide vari-ety of prepared foods including appetizers,soups, sauces, casseroles, crackers, fillings
in pastry and pies as well as the popularuse of cheese as a topping on pizzas andas cheese slices on hamburgers and cold(sub)sandwiches. There have been severalexcellent reviews on the functionality re-quired of cheese when used as a food ingre-dient [23, 25]. Some of the uses of cheeseas a food ingredient are listed in Table Ialong with some of the characteristics thatare required from the cheese when used inthese products.
In our previous reviews we have de-scribed some possible physico-chemicalbases for textural properties [53] andthe important role for calcium phos-phate in modulating cheese functional-ity [39]. In the present article the fo-cus will be on key performance attributes,both in the unmelted and melted state,for cheese when used as an ingredient.Some selected parameters that influencethese performance attributes are discussed.End-users of cheese demand consistent
Cheese as a food ingredient 575Ta
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576 J.A. Lucey
performance in their food products socheese manufacturers have focussed theirattention on various strategies to reducechanges in functionality during ripening.Cost is another critically important param-eter as cheese is usually the most expensiveingredient in a food product. In the US, inaddition to traditional ingredient cheeses,like Cheddar and low moisture part-skimMozzarella, cream cheese is an importantingredient cheese. Cream cheese is usedas an ingredient in cheese cakes and inspreads; some of the key textural attributesof this cheese type are also discussed.
2. CHEESE FUNCTIONALITY
There are a number of key parametersthat are routinely manipulated to controlthe functionality of cheese. These parame-ters are often targeted in ingredient cheeseslike Mozzarella [42–44, 73], but these pa-rameters can be exploited as techniques toalter the functionality of other cheese vari-eties. Some general comments about theseparameters are discussed below, see previ-ous reviews on cheese functionality (listedpreviously) for a more extensive descrip-tion of factors influencing cheese function-ality.
2.1. Parameters influencing cheesefunctionality
2.1.1. Composition
Higher moisture cheeses are softer,smoother and more flowable than a simi-lar (e.g. age, pH, calcium content) cheesethat has a lower moisture content. Low fatcheeses tend to be harder and less meltablethan higher fat cheeses [17] unless cor-rective measures are taken by the cheesemaker to alter these characteristics (e.g.by increasing the moisture content). De-creasing the fat content or reducing the
calcium content of cheese results in a pro-portional increase in the protein and mois-ture contents. Cheeses with high proteincontent have an increased concentration ofcrosslinking material per unit area of thematrix compared to cheeses with lowerprotein contents, unless steps are taken toreduce protein-protein interactions (e.g. byreducing the ratio of insoluble calcium toprotein or waiting for ripening to causeproteolysis). Cheeses with the same pro-tein content but with a higher ratio ofαs-casein to β-casein have greater melta-bility [66].
Legal compositional limits often deter-mine the moisture and fat contents of aparticular cheese variety (e.g. the Codeof Federal Regulations in the US). Thereare many ingredient cheeses that havetheir own specific compositions and theyare classified as non-standard cheese (e.g.pizza cheese or process cheese product)since they are designed to have specificindustrial functionality. Lowfat or nonfatcheeses are used by product developers inorder to meet specific nutritional targets.
2.1.2. pH (acidity)
Milk is a stable product because ca-seins have a net negative charge. Even ifmilk is gelled and made into a fresh cheesewithout significant acid development thecurd is not able to stretch and melt due toexcessive calcium phosphate crosslinkingof caseins (e.g. Queso Fresco). Acidifica-tion removes calcium from within caseinparticles, i.e., colloidal calcium phosphate(CCP), and makes them more flexible,which is important for stretch [52, 53].A critical amount of acidification is em-ployed in cheeses, such as Mozzarella, sothat it will have the desired melt, stretchand flow characteristics. If there is exces-sive acidification (pH < 4.9, e.g. Creamcheese, Feta) the curd loses its melt andstretch characteristics due to excessive:
Cheese as a food ingredient 577
protein attraction (electrostatic and hy-drophobic) between caseins [53]. The rateand extent of acid development duringcheesemaking controls the calcium contentof cheese and this rate can be changed byaltering the pH at critical points during theprocess [52], the use of calcium chelatingacids (e.g. citric acid) [41] and the use of awash or whey dilution step to remove lac-tose/salts, e.g. Colby (a washed-type Ched-dar cheese), Swiss (although not all Swisscheesemakers use a wash or whey dilutionstep) or Gouda cheese.
2.1.3. Temperature
Temperature affects the association ofcasein molecules as they expand at lowtemperature due to the weakening of hy-drophobic interactions. Low temperaturesresult in increased contact area betweencaseins and this causes the increasedfirmness [53]. Caseins contract with in-creasing temperature due to strengtheninghydrophobic interactions so firmness de-creases [53]. Heating results in a collapseof the cheese network and the pooling offree oil [2, 24]. The marked variation incheese texture with changing temperatureis exploited to help shred cheese when itis cold so that it is firmer and easier tocut cleanly. The softening that occurs athigh temperatures is widely exploited forthe use of cheese as an ingredient in a rangeof baked foods. Over-ripe Camembert isrunny even at refrigeration temperatures.
2.1.4. Milk heat-treatment
High heat treatments of milk (greaterthan pasteurization, or multiple pasteuriza-tions) or other dairy ingredients (e.g. but-termilk [22]) causes a high level of wheyprotein denaturation. The denatured wheyproteins interact with casein and result in acheese with restricted melt and flow. The
addition of acid to hot milk is used forthe manufacture of several fresh cheeses(e.g. Ricotta, Queso Blanco). Acid-heat co-agulated cheeses are non-melting cheesedue to the formation of the covalent bondsbetween proteins (caseins and whey pro-teins) and these bonds hold the cheesematrix together even at high temperatureswhen changes to other interactions usuallypromote greater mobility of the network(which results in melt and flow).
2.1.5. Homogenization
Homogenization reduces the average fatglobule size and greatly increases the fatsurface area. Caseins and whey proteinsare the main emulsifiers on this new inter-face. Homogenization of milk and creamis practised in the manufacture of bluecheese in order to increase lipolysis, whichincreases the concentration of free fattyacids, ketones and other flavor compounds.Homogenization of milk and cream ispractised for Cream cheese, which is madefrom high fat milk (e.g. 12%), and homog-enization increases the consistency of thistype of acidified products as the proteinson the newly created fat particles becomean active part of the gel network. Homog-enization also increases the moisture con-tent of rennet-coagulated cheese by im-pairing the rearrangement and shrinkage ofcaseins that are responsible for syneresis(moisture loss) [37]. For natural cheeses,homogenization of milk and cream hassometimes been practised for lowfat Ched-dar [57] and this can reduce the hardnessand restrict the melt of these cheeses byinterrupting the dense protein matrix. Ho-mogenization is often practised for freshHispanic types of cheeses where restrictedmelt is required. Homogenization is usedfor cheeses “filled” with vegetable oils orwhere nutritionally valuable oils are addedto cheese (e.g. oils rich in ω-3 fatty acids).
578 J.A. Lucey
Recently, the impact of the milk fatglobule size on cheese properties has beeninvestigated [58, 59]. Microfiltration, withvarious membrane pore sizes, was usedto produce milk fat fractions with small(∼ 3 μm) or large (∼ 6 μm) size glob-ules. Small globules contain more shortchain fatty acids [9]. Camembert cheesewith small globules retained more mois-ture than cheese with larger globules [59].Emmental cheese made with small fatglobules had lower lipolysis and more in-tact fat globules whereas more destabi-lized fat was observed in cheese madewith large globules. The functional proper-ties of Emmental cheese made with smallfat globules were improved with increasedstretching, melting and lower extrusionforce compared to cheese made with largerglobules [58]. Smaller fat globules resultsin an increase in the number of fat glob-ules and fat surface area compared to acheese with the same fat content but largeraverage particle size. Presumably, the in-creased fat surface area due to the pres-ence of small native fat globules wouldcause more disruption to the continuity ofthe casein matrix in cheese, which mightbe the reason for the observed textural dif-ferences in cheese made with small fatglobules.
Changes in the structure of milk fatduring the manufacture and ripening ofEmmental cheese has been studied [50].Fat globules were physically entrapped inthe initial rennet coagulum but heating andpressing of curd grains caused aggrega-tion and coalescence of fat globules. Inripened Emmental, three main forms ofmilk fat were identified: (i) small fat glob-ules still covered by the native milk fatglobule membrane; (ii) aggregates of par-tially disrupted fat globules; and (iii) freefat, resulting from the disruption of themilk fat globule membrane. In cheeses,like Camembert, that are subjected to lessheating of the curd grains and little or nocurd pressing, the size of the milk fat glob-
ules in these cheeses are in the same rangeobserved for the initial cheesemilk [49].
2.1.6. Use of exopolysaccharide-producing (EPS) cultures
Over the past 10 years there have beennumerous studies on the impact of usingEPS-producing cultures on the texture oflow fat Mozzarella (e.g., [69]) or reducedfat Cheddar cheeses [3, 12]. The forma-tion and structural properties of the vari-ous types of EPS produced by lactic acidbacteria have been reviewed [15, 84]. Theproduction of EPS during cheesemakingresults in cheeses with increased mois-ture content and altered textural proper-ties. The increased moisture content maybe due to EPS in some way interferingwith the casein-casein rearrangements thatare necessary during syneresis to removemoisture from curd grains. Another pos-sible explanation is that these EPS physi-cally trap moisture within the curd parti-cles, as they are hydrocolloids, and thus,there may be less freely available wa-ter lost during cooking/pressing. The im-proved texture and melting properties thatare reported in experiments with EPS-producing cultures are at least partly dueto the increased moisture content in theEPS cheeses. The mechanism by whichEPS influences the texture of dairy prod-ucts like fermented milks and cheese isunclear [32, 83]; some studies argue thatthe amount of EPS-produced is too lowto have a functional impact, other suggestthat there is a physical attachment of theEPS with the casein matrix [33] while oth-ers suggest that there is incompatibility be-tween EPS and milk proteins (e.g. [80]).There are also concerns about the impactof EPS on whey processing and whey func-tionality; the use of some types of ropystrains for cheesemaking increased the vis-cosity of whey during the concentrationstep [70] whereas the EPS produced by
Cheese as a food ingredient 579
some other strains may not have a large im-pact on the viscosity of whey [12, 70]. Theuse of EPS cultures in cheesemaking hasrecently been reviewed [32].
2.1.7. Use of transglutaminase
Transglutaminase (TGase; EC 2.3.2.13)catalyses covalent intermolecular proteincross-linking through an acyl-transfer re-action, between the γ-carboxyamide groupof a peptide-bound glutamine residue (acyldonor) and the primary amino group ofan amine (acyl acceptor). The applicationof TGase in various types of dairy prod-ucts has been reviewed [38]. In a systemwhere caseins and whey proteins are avail-able as substrates for TGase, such as milk,the caseins are preferentially cross-linkedover native whey proteins [30]. Various ap-proaches have been used for TGase treat-ment of cheese. Milk could be treated withTGase, held at some suitable temperatures(e.g. 20 to 40 ◦C) for the reaction to oc-cur and then a high heat treatment of milkor a cook step in the cheesemaking pro-cess used to inactivate the enzyme. How-ever, one issue is TGase action results inthe inhibition of rennet coagulation. Alter-natively, cheese curd can be treated withTGase, some hold time allowed for thecrosslinking to occur, and then the en-zyme inactivated with heat; this approachhas been used to improve the firmness ofprocessed cheese [85]. Cream cheese withimproved recovery of whey proteins andincreased firmness has been reported aftertreatment with TGase [31]. Increased pro-tein crosslinking by TGase could also re-duce meltability.
2.2. Unmelted cheese functionalityand performance
Unmelted cheese is subjected to a widerange of cutting and size reduction op-erations (e.g. shredding, slicing, grating,
dicing, cubing, pureeing, crumbling, gran-ulating, etc.) for food service or retail pur-poses. There are a number of functionalattributes that are important for these op-erations:
2.2.1. Firmness/hardness
Cheese firmness increased by low mois-ture or low fat contents, and decreased bylow insoluble calcium to protein contentor low casein to fat ratio in cheesemilks.For Cheddar (and other medium to lowmoisture cheeses) firmness (at refrigera-tion temperature) does not change muchduring ageing in contrast to higher mois-ture cheeses (e.g. Mozzarella), which be-come softer and stickier with age. A lowhardness and a medium to low yield stressvalue are required when cheese is used asa spreadable material.
2.2.2. Brittleness (short texture)
Short texture can be caused by low pH(e.g. crumbly Cheshire or Feta cheese),high salt, reduced calcium content, exces-sive proteolysis (e.g. very mature Cheddarcheese) or low moisture cheeses (e.g. hardgrating Italian cheeses). The presence ofhigh amounts of denatured whey proteinswhen combined with caseins in a cheesematrix can also make the cheese shorter.Cheeses with a surface rind (e.g. Gouda)become shorter and more brittle with agepartly due to moisture loss. Ricotta has ashort, particulate texture which is usefulin pasta dishes where melt or stringinesswould be undesirable.
2.2.3. Machinability
Machinability is a vague termfor the ability for the cheese to becut/sliced/shredded by machine (e.g. wires
580 J.A. Lucey
or high speed knifes). This attribute isinfluenced by cheese hardness (needs tobe moderate to high), brittleness (shouldnot be too “short” or it will be crumblyand will produce a lot of fines), and lowadhesiveness (if the curd is too adhesive itwill be stick to the metal). For pressure-sensitive adhesives it has been reportedthat tack (sticking) will not occur whenthe storage modulus of the adhesive isgreater than 105 Pa but tack also dependson surface energies of the adhesive andadherend (in this situation the machinesurface) [11]. Machinability is influencedby cheese composition, pH, protein break-down, and temperature of operation. Inpractice, machinability is controlled by theempirical selection of a suitable range forthese parameters for an individual cheesevariety, e.g., some cheeses may be suitablefor shredding within a few days whileothers may be shredded for up to a fewmonths. Shreddability is a broad term thatis used to encompass many characteristicsof shredded cheese including the ease ofprocessing, the shape and integrity of theshreds, the propensity of shreds to mat orremain free-flowing, and the propensityto form fines during shredding [11]. Mostsize reduction operations are performed atroom temperature although the cheese maybe much colder; if cheeses are soft thenthey may be cooled to low temperaturesto assist in increasing their firmness andthereby improve their machinability.
Some cheese types are difficult to sliceor shred, e.g., Feta or Blue cheese, dueto their short, crumbly texture. The cheeseindustry developed an alternative size-reduction approach of crumbles exploitingthe short texture of these cheeses. Cheesecrumbles are very suitable for sprinklingon salads and baked pizzas.
2.3. Cooking and melting properties
Melted cheese has found a vast num-ber of applications, e.g. as a pizza top-
ping, cheese slices on hamburgers, toastedsandwiches, fillings, layers in lasagna, andsauces. The end-users of cheese have veryspecific requirements for what kind ofmelt performance they want from theircheese. Cheese manufacturers can manip-ulate cheese performance to consistentlymeet these specifications. The functionalproperties of melted cheese are complexand we can distinguish at least seven im-portant attributes namely flow, softening,shred identity, stretchability, tenting, blis-tering and browning.
2.3.1. Flow (e.g. flow-off a pizza crust)
Flow increases with age (due to pro-tein breakdown/proteolysis, and ongoingloss of insoluble calcium from casein par-ticles) and with an increase in the mois-ture or fat contents. There is very littleflow in low pH (< 4.9) cheeses, e.g. cot-tage or Feta. Flow is increased by a reduc-tion in the calcium content. Cheeses withrestricted flow can be achieved by highmilk heat treatment, very high pH (> 5.9)or very low values (i.e. < 4.9). Processcheese with restricted melt/flow can beachieved by the use of specific emulsifyingsalts (ES) (e.g. pyrophosphate) or the useof high temperatures and long hold timesduring curd cooking. Many Hispanic-stylefresh cheeses, such as Panela, soften whenheated but do not melt and flow due tothe high pH (e.g. 6.4 to 6.5). Panela, andsimilar types of fresh cheeses, are widelyused as a topping on tacos, chili and bur-ritos. The use of acid to precipitate hotmilk is exploited for a number of cheeses,e.g. Queso del Pais and Ricotta, and thesecheeses soften but do not flow. A widerange of cheeses are manufactured withvery different texture and flow properties.The dynamic rheological profiles of a num-ber of different cheese varieties duringheating have been reported [24, 71].
Cheese as a food ingredient 581
It is sometimes suggested that changesin casein solvation or hydration is a keydeterminant of melt/flow but as discussedby Lucey et al. [53] cheese already has avery high water activity and there is veryrapid exchange of water molecules fromthe interior of caseins to the bulk serum.Thus, water mobility does not appear to bea limiting factor in inhibiting melt. The ob-served age-related changes in expressibleserum in some high moisture cheese, likeMozzarella, are caused by solubilisationof CCP and brine uptake into the cheesematrix.
2.3.2. Softening during heating
This happens in all cheeses, the ex-tent depends on composition, age and pH.Softening is caused by a reduction in thestrength of the casein interactions withincreasing temperature (as indicated bythe reduction in the elastic moduli) andcontraction of the network [24]. Ther-mal energy from heating promotes greaterbond mobility (especially at temperatures> 35 ◦C, as indicated by the increase in theloss tangent parameter during the heatingof most natural cheeses).
2.3.3. Shred identity after heating
This refers to individual shreds still visi-ble after baking, which was caused by lackof softening and especially flow. Less com-mon in aged cheeses as flow increases withage. Visible shreds can also be caused byexcessive use of anticaking agents so theseingredients have very high melting pointsand if they completely coat the shreds thiswill keep the surface dry, preventing mois-ture or fat release and thus inhibit flow.Low moisture cheeses like Parmesan mayexhibit shred identity after heating (oftengrated or finely ground Parmesan is usedinstead of shreds).
2.3.4. Stretchability of curd duringcheesemaking
Curd stretches when sufficient calciumis lost from caseins during cheesemak-ing, e.g. pH ∼ 5.2 in cultured Mozzarellabut occurs at pH ∼ 5.6 in direct acidMozzarella [52]. The direct addition ofacid to the cheese vat is more efficient ap-proach to the removal of insoluble calciumthan the cultured product where muchof acid development occurs after wheydrainage. The pH at which curd becomessuitable for stretching also depends onextent of demineralization (e.g. by pre-acidification with some acid helps to re-move more CCP [41]), and fat and caseincontents. Low fat or high casein (concen-trated) milks require a lower pH at rennetaddition or of the final cheese pH to get thecurd to become suitable for stretching.
2.3.5. Stretchability of cheese in itsend-use application
A lot of cheese is used as an ingre-dient on pizza. Stretchability is the abil-ity of the melted cheese to form fibrousstrands that elongate without breaking un-der tension during ripening [43]. Stretch“quality” is important, as many consumersdo not want long “strings”. Thus, thelength, tension and type of stretch (strings,feathering or fibrous) are important qual-ity attributes. Many young cheeses exhibitstretch (e.g. Cheddar) but during ripen-ing the stretch quality decreases and thecheese may become stringy. During ageingof Mozzarella the length of stretch initiallyincreases but after 3–4 weeks cheese maybe “soupy” and the strands become shortand weak [53].
2.3.6. Tenting
This term is usually used to refer tobulging of the cheese that may occur over a
582 J.A. Lucey
large area during baking due to the entrap-ment of water vapor. If this bulging occursover a small area it is referred to as blis-tering. In reduced or low fat cheeses thisprocess helps a surface “skin” to form; thisskin may dry out and burn/brown duringbaking.
2.3.7. Blistering and skinning
This refers to small visual bubbles onthe pizza surface. It is influenced by thetextural (rheological properties of the sur-face) properties of cheese, which some-times do not allow gas bubbles to escapefrom the surface (unlike a “soupy” prod-uct). Skinning is another surface defect thatis often seen in nonfat cheese after bakingor during cooling. Skinning describes theformation of a tough (dry) surface layer,which in nonfat cheese may seem like aclear plastic sheet.
2.3.8. Browning
During baking the color of somecheeses increases due to a Maillard reac-tion between reducing sugars (e.g. lactose)and proteins (especially amino acids). Thecolor can range from light straw, to goldenbrown to black depending on the sever-ity of the baking process, the concentra-tion of reducing sugar and the type of ovenused. Browning can be reduced by wash-ing the curd as this reduces the lactose con-tent and by selecting starter cultures so thatall the residual sugars (including galactose)are metabolized. Other cheese manufactur-ing conditions can be varied to facilitatecomplete sugar fermentation, e.g. allowingmore time at suitable temperatures to en-courage continued bacterial fermentationprior to cooling or brining. Cheeses withslight browning or completely white are of-ten requested by consumers. Aged cheesescontain amino acids that are sensitive to
Maillard reactions if some residual reduc-ing sugars are still present. A reductionin the water activity of cheese promotesthe Maillard reaction and contributes to thegreater browning of cheeses like Parmesan(that occurs even at low temperatures).
In some types of cheese (e.g. Parmesan)there may be little or no residual sug-ars after a short aging period andyet these cheeses can in some situ-ations undergo browning. Some typesof lactobacilli have been shown to beable to produce various carbonyl com-pounds, e.g. α-dicarbonyls [72], whichare more reactive compounds than sugarsfor Maillard-induced reactions [79]. Lac-tobacilli species and strains vary greatly intheir abilities to produce α-dicarbonyls [7].Thus, browning in some aged cheeses maybe due to the metabolism of nonstarter lac-tic acid bacteria, like lactobacilli, and sometype of favourable environmental condi-tions (e.g., Aw, redox) for the Maillard re-action.
Hexose oxidase (EC1.1.3.5) has beenused to reduce browning of cheese shredswhen they are used in baking applications,e.g. on pizza [78]. Hexose oxidase oxidizesthe reducing groups on sugars like glucose,lactose and galactose preventing their in-volvement in Maillard reactions. Oxygenis required for this oxidation reaction so anaerobic environment is needed. This treat-ment is done after cheese manufacture oth-erwise this reaction could inhibit bacterialfermentation of lactose.
2.3.9. Free oil formation
This is the tendency of free oil to sep-arate from the melted cheese and formoil pockets, particularly at the cheese sur-face. Excessive oiling-off leads to a greasy,shiny surface. Free oil increases with ageof cheese due to ongoing proteolysis.High salt levels have been reported toreduce free oil formation in Mozzarella
Cheese as a food ingredient 583
cheese [14]. Some types of nonstarter cul-tures may metabolize glycoproteins in themilkfat globule membrane as a carbohy-drate source [1] and it is possible that themetabolism of membrane components mayweaken its integrity. Free oil may be ben-eficial in helping to control browning andblister formation [75]. Process cheese hasvery little free oil due to emulsification offat by caseins during the heating and shear-ing that is used in the cooking process. Lit-tle free oil is released in cheese made fromhomogenized milk [74]. Treatment of milkfor Mozzarella cheesemaking with phos-pholipase has been reported to reduce fatlosses in the cooker stretcher and result incheese with less free oil formation duringripening [67]. Lilbaek et al. [47] suggestedthat lysophospholipids released from thefat globule membranes by the action ofphospholipase act as surface-active agentsin the cheese curd, helping emulsificationof water and fat during cooking.
2.3.10. Method of heating
The type of oven used for baking canhave a major impact on cheese perfor-mance. Various heating methods, e.g. gas,electric or wood burning ovens are usedfor pizza and other dishes. For pizza, vari-ous types of convection or forced air (fan-assisted) ovens are common in food ser-vice operations as they give more rapid andeven heating than conventional ovens. Onepopular type is the Impinger� oven wherehot air under pressure is forced down onthe cheese. This results in rapid heating asthe cheese moves through the oven on aconveyor belt. But the jets of hot air alsodry out the cheese surface and this ovenis more likely to result in blistering andbrowning of a cheese. The trapped watervapor finds it harder to be released fromthe surface, which can lead to a bulgingup of the cheese. As blisters are formedthey are more prone to drying-out, which
favors the Maillard reaction and as a re-sult browning is greater in forced-air orImpinger ovens. In conventional ovens, thebaking process is slower, which is whyforced-air ovens are so popular. For disheslike lasagne, very long cooking times inconvection ovens can also lead to morerisk of the surface drying-out unless thedish is covered for some of the time. Mi-crowave ovens are often used for quickreheating of foods, including pizza, butthey do have the tendency to make thebase either brittle or very soft dependingon the ingredients used and the cheese it-self can get tougher than in a conventionaloven. Some frozen pizza suppliers alsoprovide accessories, e.g. a crisping sleeve,to help bake the pizza in a microwave. De-pending on the type of oven, the heatingtemperature and cooking times for pizzaand other cheese dishes vary. Regular pro-cessed cheese generally have lower melttemperatures than natural cheeses like lowmoisture part-skim Mozzarella so the heat-ing or baking conditions can be reduced.For applications where process cheeses aresubjected to high temperatures (e.g. re-torting) then cheeses with restricted meltare used. Sauces or fondues can be read-ily heated or reheated in a microwave.The food service sector also uses differenttypes of ovens including systems that uti-lize multiple forms of heating.
Cheese manufacturers provide cheesethat can perform as an ingredient un-der very specific oven types and heatingregimes (temperatures and times). Manyfood service operations use blends ofcheese in a variety of dishes and fast-food products. These melts are formulatedto consistently deliver the desired flow,stretch, color and flavor. Cheese is shred-ded, blended, grated and dehydrated andready for food service operations. Cheesecan be individually quick frozen (IQF) af-ter shredding or dicing to provide a conve-nient and stable (frozen) product for end-users to use on products like pizza, hot
584 J.A. Lucey
sandwiches, and Mexican-style dishes. Insome situations there can be interactionsbetween the cheese topping and other foodingredients like the sauce on a pizza.
3. ROLE OF INSOLUBLECALCIUM ON CHEESETEXTURE FUNCTIONALITY
The importance of calcium and phos-phate interactions for cheese textural prop-erties has been reviewed [39, 52, 53, 55].It has been recognized for more than100 years that rate of acid development hasa key impact on cheese quality and tex-ture. Cheesemakers later came to recog-nize that acid development directly influ-enced the Ca content of cheese and that thetotal Ca content was an important parame-ter for determining cheese texture [45]. Bythe late 1980 and early 1990s, there was therealisation that natural rennet-coagulatedcheeses, like Cheddar and Emmental, con-tained a high concentration of insolubleCa [52, 63]. In milk at low pH values(≤ 5.2), the CCP is completely dissolvedso why does so much of the CCP appear toremain undissolved in cheese? When aciddevelopment in cheesemaking occurs inthe vat prior to whey drainage, the moisturecontent of the curd particles is high and thesolubility of CCP as a function of pH issimilar to that in milk. When much of theacid development occurs later in the pro-cess, e.g. in the hoop or when the curd par-ticles are lower in moisture content it ap-pears to be more difficult to dissolve CCP.This may be the explanation for the keyrole that the pH at rennet addition has onthe total Ca content of cheese [52]. Duringthe first few weeks after cheese manufac-ture, and especially in the first few days,there is a decrease in the proportion of in-soluble Ca as a function of the total Cacontent of Cheddar cheese from ≥ 70%at day 1 to ∼ 60% after 4 weeks [34].Shifts in the Ca equilibrium have been ob-
served for several other cheese types, e.g.Mozzarella [28]. If the cheese become veryacid, e.g. pH 4.7, then the insoluble Cacontent of Cheddar decreases during ripen-ing but the levels still remain ≥ 40% [46].What limits the extent of the solubilisa-tion of insoluble Ca in cheese at such lowpH values? It appears that the solubili-sation of insoluble Ca in cheese causesa rapid increase in the serum Ca con-tent up to some maximum concentration(e.g. [46]). When the Ca content of cheeseserum is very high (> 800 mg·100 g−1)it becomes very susceptible to precipita-tion of calcium phosphate [65]. This pos-sible mechanism is shown in Figure 1. Alower (maximum) serum Ca concentration(∼ 700 mg·100 g−1) has been reported invery low pH Cheddar cheeses [46]; pre-sumably the pH and moisture content ofcheese influence the maximum serum Caconcentration possible before precipitationoccurs and therefore further solubilisationof insoluble Ca is unfavored. O’Mahonyet al. [65] were able to increase the total Caand insoluble Ca content of cheese by theincubation of cheese in buffers containinghigher serum Ca concentrations than thosepresent in the serum phase of cheese. Pre-sumably, this was possible because therewas a large increase in moisture content ofcheeses incubated in these artificial cheeseserum buffers. It is now becoming com-mon for cheese researchers, and by somedairy companies, to monitor the insolubleCa content of cheese during ripening togain greater control over cheese function-ality.
4. STRATEGIES TO EXTEND THEPERFORMANCE WINDOW OFCHEESE FUNCTIONALITY
For ingredient cheeses, like low-moisture part-skim Mozzarella cheese,there is an initial period where cheesefunctionality is not suitable, e.g. it may
Cheese as a food ingredient 585
Ripening time (weeks)0 2 4 6 8 10 12 14
Cal
cium
con
cent
ratio
n in
che
ese
seru
m
500
550
600
650
700
750
800
1. Acid development (pH drop or history)
2. Cheese moisture content
3. Total Ca content4. pH increase (e.g.
Swiss)5. Formation of crystals
Figure 1. Possible factors affecting the “equilibrium” serum Ca concentration in cheese.
exhibit poor melt or free water. After someripening period acceptable performanceis obtained due to the influence of tworeactions (Fig. 2a). Firstly, a shift of someof the insoluble Ca associated with caseinto soluble Ca in the serum phase [34, 54].Secondly, ongoing proteolysis results inthe hydrolysis of some bonds on mostlyαs-casein, as β-casein is only slowlyhydrolyzed during the ripening of mostcheese varieties, e.g. Cheddar. In cookedcheeses plasmin activity becomes moreimportant during ripening due to the denat-uration of chymosin [16]. In high cookedcheeses, like Swiss, β-casein is usuallyhydrolyzed faster than αs1-casein [82].To reduce the extent of proteolysis inSwiss cheese during ripening manycheesemakers now omit Lactobacillushelveticus as a starter culture due to itsstrong proteolytic activity and insteadmany use only Lactobacillus delbrueckiisubsp. lactis [20].
Recently, O’Mahony et al. [64] addedpepstatin (a powerful inhibitor of rennetactivity) to whey during Cheddar cheesemanufacture in order to inhibit residualrennet activity during cheese ripening.
There was a significant reduction in hard-ness during the first 21 d of ripeningeven in cheese where there was no resid-ual rennet activity. O’Mahony et al. [64]concluded that hydrolysis of αs1-casein atPhe23-Phe24 is not a prerequisite for soft-ening of Cheddar cheese during the earlystages of ripening. They proposed that thisinitial softening of texture is principallydue to solubilization of some of the CCPassociated with the para-casein matrix ofthe curd.
Many cheese manufacturers would liketo be able to extend that acceptable perfor-mance period for their cheese to increasethe shelf-life of its use as an ingredient andto improve consistency of performance.Ideally, this would produce a cheese wherethere no biochemical or microbiologicalactivity and where a stable state of Cain cheese was achieved immediately aftermanufacture (Fig. 2b). In many respects ashelf-stable cheese is similar to the charac-teristics of processed cheese. A summaryof some of the various strategies for re-ducing changes in cheese functionality aregiven in Table II.
586 J.A. Lucey
0 20 40 60 80
Prot
eoly
sis
(PTA
sol
uble
N a
s a
% o
f Tot
al N
)
2
4
6
8
10
12
14
16
18
Inso
lubl
e C
alci
um a
s a
perc
enta
ge o
f tot
al C
alci
um
56
58
60
62
64
66
68
70
Ripening time (days)0 20 40 60 80
0
2
4
6
8
10
12
14
16
18
56
58
60
62
64
66
68
70
Insoluble Calcium Proteolysis
(a)
(b)
I II III
Figure 2. Comparison of ripening changes in aMozzarella cheese (a) and a shelf stable cheese(b). During cheese ripening there is a reductionin insoluble Ca content as a % of total Ca (Cashift) as well as ongoing proteolysis (schematicexample only). For a cheese like Mozzarella (a)these changes results in three zones of func-tional performance: (I) young cheese is toughand has poor melt, (II) acceptable performancewindow (good melt, stretch and shred), and (III)unacceptable performance window (cheese be-comes too soft, soupy and sticky) (modifiedfrom [39]).
4.1. Use of dry dairy ingredientsinstead of milk
There are many reasons why cheesemanufacturers sometimes use added dairyproteins in cheesemaking: (i) standardizethe protein and/or fat content of cheesemilkwhere skim milk powder, condensedmilk/buttermilk, retentates from membranefiltration, or milk protein concentrates maybe added (depending on regulations in each
country as to what is permitted to beused in a particular cheese variety); (ii) re-constitution of milk for cheesemakingwhere cheese can be made on-demand (di-rectly from powders when required) [61],powders can be used for cheesemakingin countries where there is little fluidmilk and powders can be used to ex-tend existing milk supplies (i.e. make morecheese than what is possible with only lo-cal milk); (iii) improve efficiency/increaseyield/reduce costs, e.g. use of high con-centration factor UF to retain more wheyproteins, as a substitute for young cheese(e.g. cheese base) in process cheese, andsubstitute cheese solids with dairy pro-teins/powders (e.g. process cheese) [62];(iv) eliminate the need for a whey separa-tion step [29, 48, 77]; (v) alter functional-ity: this includes control of melt, increasedsmoothness of soft cheese, and reduce theamount of ES required for process cheese.Dairy proteins, such as, milk protein con-centrates, are also being modified duringtheir manufacture to improve their char-acteristics in cheese, e.g. modification oftheir calcium and denatured whey proteincontents [8].
4.2. Process approaches to reduce“ripening” changes
In Mozzarella, the high curd tem-perature in the cooker stretcher reducesbacterial numbers and lowers residual en-zyme activity during ripening; these pro-cess conditions help this high moistureproduct have good melting functionalityover a typical one month refrigerated stor-age shelf life. Plasmin may remain activeas it is more heat-stable that chymosin.Most cheeses will require refrigerated stor-age prior to use and some will be heldfrozen. Various strategies for reduce ripen-ing changes in cheese functionality werelisted in Table II. Manufacturers can slowdown ripening changes, which facilitate
Cheese as a food ingredient 587
Table II. Summary of some strategies that have been used to reduce the extent of changes in cheesefunctionality during storage (extend the performance window).
Chemical/Biologicalchanges targeted
Methods/Treatments
Milk
Bacterial/enzyme activity Heat, CO2 addition, microfiltration (MF), non-thermal processes
Seasonal or milk supply variationsRatio of proteins/minerals
Reconstitution of cheese milk from dairy pow-ders or the use of retentates (pre-cheese)
Ratio of total and insoluble Ca toprotein
Preacidification, direct acidification, additionof Ca sequestrant, altered rate of acidification
Ratios of individual caseins Use of cold MF of cheesemilk to remove somebeta-casein
Additional protein crosslinking Use of transglutaminase, attachment of dena-tured whey proteins to caseins
CurdRatio of total and insoluble Ca tocasein
Preacidification, direct acidification, additionof Ca sequestrant, altered rate of acidification
Residual rennet, other enzymesand starter culture activities
Cooking treatment (time and temperature ofcurd in the cheese vat or in the mixer/molder)to denature rennet and other enzymes and re-duce bacterial numbers,High salt to inhibit bacterial growth/activity
CheeseState of Ca in cheese (e.g. prevent-ing solubilization of insoluble Caduring ripening)
Addition of Ca sequestrant during cheese man-ufacture,Prevent pH changes post-manufacture bywashing/diafiltration or using salt sensitiveculturesHigh pressure processing
Residual rennet, other enzymesand starter culture activities
Use of very low storage temperatures, frozenor individually quick frozen (IQF) cheeseHigh pressure processing
Process cheeseState of Ca in cheese Addition of Ca sequestrant
Residual rennet, other enzymesand starter culture activities
Heating/pasteurization treatment
shipment of their cheese over long dis-tances, e.g. overseas. Slowing ripeningchanges in natural cheese could be helpfulto the manufacturers of processed cheeseas they require young cheese with a highlevel of intact casein in their formulations(e.g. slices), and during ripening the in-tact casein content of natural cheese de-clines [40].
High pressure processing (HPP)(> 400 MPa) of cheese curd has beenapplied to reduce proteolysis during
ripening [10]. HPP has been used to im-prove the meltability of young Mozzarellacheese [40]. It is known that high pressureprocessing solubilises some of the insol-uble Ca in milk but most of this changeis restored during subsequent storage(after pressure release) of HPP-treatedmilk [21, 36]. It is not clear what theimpact of HPP is on the insoluble Cafraction in cheese. The impact of HPP oncheese properties has been reviewed [51].Moderate (345 MPa) to HPP of 1-d old
588 J.A. Lucey
Cheddar cheese curd has been reported toimprove the shredding properties, whichcould allow earlier shredding of this milledcurd cheese [76].
4.3. Blurring the lines betweennatural and process cheese
There have been a number of reportswhere ES have been added to “natural”cheese in order to modify cheese function-ality [4–6,56,60,68]. Emulsifying salts arenot listed as optional ingredients in mostcurrent standards of identity for variouscheese varieties (including Mozzarella), soother terms like pasta-filata type cheeseor pizza cheese are used to describe thesecheeses. The ES are sometimes addedinto the starter culture media, or with the(dry) salt or in a cooker for cheeses likeMozzarella. The growth in waterless or drycookers for Mozzarella cheese [13], whichare more like process cheese operations,has made it easier to incorporate these in-gredients without concerns for losses intothe cooker water. In recombined cheesesor analogue cheeses, ES are often added tohelp hydrate milk ingredients and improvetheir ability to emulsify the added fat. Theuse of ES offers the potential for greaterconsistency of cheese performance by con-trolling the state of Ca in cheese and avoid-ing the ongoing solubilisation of insolubleCa that occurs during the ripening of nat-ural cheese. Traditional processed cheesesdo not perform as well as Mozzarellacheese for pizza type applications since themilkfat is completely emulsified in pro-cess cheese and the release of fat duringbaking is considered to reduce scorching.Processed cheeses are usually not stringy.So a “partially processed” but still “nat-ural” cheese has some advantages, espe-cially for the use of these cheeses as in-gredients in various foods where standardsof identity are often less important thanfor retail cheese. A greater range of cheese
types (e.g. Feta, Blue, Cream cheese) arenow also being subjected to processing inaddition to the commonly used ingredientcheese, like Cheddar and Emmental. Dur-ing processing flavors or condiments canbe added and processing also facilitates amodification in the original cheese texture.
5. CREAM CHEESE ASAN INGREDIENT IN FOODS
Cream cheese includes several closely-related products including single Creamcheese, double Cream cheese, Neufchâtel(spelled Neufchatel in the US) and Bakers’cheese [26]. Cheeses that are closely re-lated to Cream cheese are produced inother countries. In the US standards ofidentity, Cream cheese must contain a min-imum of 33% fat and a maximum of 55%moisture. Cream cheese is made from milkcontaining 8–14% fat (commercially milkwith higher total solids is often used by re-duce the volume of acid whey producedat the separation step). Milk is standard-ized and homogenized (e.g., 12–17 MPaat 50 ◦C) and cooled to temperatures be-tween 31–22 ◦C for incubation. Whey isseparated from hot curd and the curd issalted, stabilizers are usually added to re-duce whey separation during storage andthe product is packaged.
Cream cheese is another example of aningredient cheese as it is mainly used as aningredient in spreads, spread on bagels andas an ingredient in (baked) cheesecakes.During heating, cream cheese exhibitsmarkedly different rheological behaviourcompared to natural cheeses (Fig. 3). Inmost natural, rennet-coagulated cheeses(e.g. Colby) the storage modulus (stiffness)decreases with increasing temperature dur-ing heating from 5 to ∼ 70 ◦C. In con-trast, cream cheese exhibits a decrease be-tween 5 and ∼ 40 ◦C and thereafter onlya slight decrease in the storage modulus isobserved. The loss tangent (ratio of viscous
Cheese as a food ingredient 589
Temperature (°C)0 20 40 60 80
Stor
age
mod
ulus
(G')
Pa
101
102
103
104
105
106
Loss
tang
ent
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Figure 3. Rheological properties of Colby (�, ∇) and cream cheese (•, ◦) during heating from 5to 80 ◦C. Open and full symbols represent storage modulus and loss tangent, respectively. Colbycheese was aged for one month. Test conditions were a maximum strain of 0.2% and a constantfrequency of 0.1 Hz.
to elastic modulus) profile during heat-ing is also very different in cream cheesewith only a minor peak observed between20–30 ◦C compared to the large loss tan-gent peak observed between 60–70 ◦Cin rennet-coagulated cheeses (Fig. 3). Itshould be mentioned that cream cheese is alow protein (e.g. 8%), high moisture (55%)product. It is likely that in a low pH, acid-coagulated product, like cream cheese,there is a lot of electrostatic attraction be-tween oppositely charged proteins as wellas hydrophobic interactions. These attrac-tive forces are sufficient to hinder soften-ing and melt at high temperatures [53].Cream cheese is often used as a major in-gredient in baked cheesecakes where soft-ening during heating is important but meltis undesirable. We have observed that thereis significant correlation (R2 = 0.7) be-tween the texture properties of different
commercial samples of cream cheese andthe firmness of cheesecake made with thesecream cheeses (Fig. 4) (unpublished datafrom Brighenti, Govindasamy-Lucey, Lim,Nelson, and Lucey). This again highlightsthe importance of controlling cheese func-tionality as the cheese can directly in-fluence the properties of foods where itis an ingredient. Figure 4 indicates thatfirmer, less spreadable cream cheese pro-duces cheesecakes that are firmer.
6. CONCLUDING REMARKS
Cheese continues to be a popular ingre-dient in a wide range of foods and dishes.The ability of cheesemakers to be ableto produce cheese that has the very spe-cific performance characteristics requiredin these foods is critical for the continued
590 J.A. Lucey
Difficulty to spread (Cream cheese)4 6 8 10
Firm
ness
(Che
esec
ake)
0
20
40
60
80
100
120
140
160
R2 = 0.7
Figure 4. Comparison of the firmness of cheesecakes (as determined by a penetration test) (unitsare in grams force) with the difficulty to spread of cream cheese (as determined by quantitativesensory analysis, anchored scale from 1–15) used as an ingredient in the cheesecakes. The creamcheeses were commercial samples with a range of fat contents (unpublished data from Brighenti,Govindasamy-Lucey, Lim, Nelson, and Lucey).
growth in the use of cheese by the food in-dustry. Once a cheesemaking method hasbeen devised to produce a cheese withthe required performance characteristics,many cheesemakers would like to be ableto extend the ripening period where thecheese exhibits these desirable properties.This has resulted in a blurring of divisionsbetween natural and processed cheese, theuse of recombined dairy ingredients tomanufacture cheese on-demand and tech-niques to restrict ripening changes. Thisnew paradigm is changing the cheese in-dustry but the key to this type of approachis a molecular based understanding of whatcontrols cheese texture and functionality.One such model has recently been de-scribed [53] and is currently being appliedto help explain cheese properties [39, 81]and ultimately this approach should helpto predict new or improved functional per-formances for cheese. Approaches from
polymer science are also being tested fortheir applicability to model and explainthe rheological behaviour of cheese [81].When a cheese is being made specificallyfor processing it is unclear why it wouldbe required (e.g., by regulations) to haveall the attributes of a table cheese, e.g. ina Swiss cheese for processing why wouldthe size and distribution of eyes be an im-portant quality attribute?
Many challenges remain including amore rigorous understanding of the molec-ular interactions that determine cheesefunctional attributes. The development oflow or nonfat cheese with functional per-formance (including flavor) approachingthe full fat version is another challengefor cheese researchers that is hindered byour lack of a detailed understanding ofhow to control the molecular interactionsbetween the caseins in cheese as wellthe biochemistry or flavor development.
Cheese as a food ingredient 591
Most detailed studies of cheese functional-ity have been performed on a few varieties(e.g. Cheddar, Mozzarella and Emmental)while a growing range of cheese varietiesare being used industrially as food ingre-dients. In the future a greater understand-ing and characterization of the functionalproperties of these other cheese varieties isneeded. That future work will reveal if theassertions discussed in this article, whichwere primarily derived from the study ofcheeses like Cheddar and Mozzarella, arevalid for other cheese types. Developinga consistent and authentic flavor in in-gredient cheeses (e.g. Cheddar) within ashort aging period also remains a chal-lenge. Enzyme-modified cheeses, exoge-nous enzymes, heat-shocked or attenu-ated cultures, or adjunct bacteria are usedto assist with flavor generation in sometypes of ingredient cheeses (e.g. pro-cessed cheese or cheese powders). Thereis also a growing trend of adding othernon-dairy ingredients (e.g. hydrocolloids,nutraceutricals) to cheeses and the impactof these materials on cheese texture, func-tionality and flavor is not well understood.
Acknowledgements: The author wants to ac-knowledge the contribution of K. Nelson(Wisconsin Center for Dairy Research) for valu-able help with Table I (uses of cheese in var-ious foods). The author also appreciates themany discussions and collaborations on thistopic with M.E. Johnson and D.S. Horne. Theauthor also wants to acknowledge the supportfor this work by the Wisconsin Milk MarketingBoard and Dairy Management Inc.
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