Milk Science Vol. 64, No. 2 2015 Review
Functional and hydration properties of milk protein concentrate (MPC)
Shinya Ikeda (Department of Food Science, College of Agricultural and Life Sciences, University of Wisconsin-Madison, 1605 Linden Drive, Madison, WI 53706, USA)
Abstract Milk protein concentrates (MPCs) are dried milk protein powders manufactured by membrane ˆltration processes such as ultraˆltration and diaˆltration followed by spray-drying. Due to their excellent nutritional qualities and phys- icochemical functionalities, MPCs are becoming widely recognized for their potential applications in the formulation of a variety of food products including protein-fortiˆed nutritional bars and beverages, and dairy foods such as cheese, yogurt, and ice cream. This review describes functional and hydration properties of MPCs, focusing on its rennet gela- tion behavior, stabilization of oil-in-water emulsions, decreases in the solubility during storage, and potential approaches to remedy the reduced solubility. Similarities and diŠerences in functional properties between MPC and other dairy ingredients such as non fat dry milk (NFDM),skimmilkpowder(SMP), and caseinates are highlighted. The eŠect of temperature and moisture during storage on the development of insolubility of MPC and its implications on the molecular mechanism of the solubility loss are discussed.
ultraˆltration of pasteurized skimmed milk6,7). Introduction During this process, caseins and whey proteins are concentrated in the retentate with maintaining Milk protein concentrates (MPCs) are dried their relative proportions, while lactose, milk salts, milk protein powders manufactured by membrane and other small molecules are removed with the ˆltration processes followed by spray-drying1,2). permeate. The ultraˆltration may be followed by MPCs have become widely utilized in a variety of diaˆltration to further increase the mass ratio of food products such as protein bars, nutritional protein to total solids8). The protein content in beverages, cheese, yogurt, and ice cream as a MPC products thus manufactured typically ranges protein source due to its excellent nutritional from 42 to 85 on the dry weight basis1).Asthe and physicochemical functional properties such protein content increases, the lactose content as gelling and emulsifying properties3～5).The decreases from ca. 46 to 4 w/w1). Although there worldwide production of MPC has increased from are no compositional standards for MPC in the 40,000 tons in 2000 to 270,000 tons in 20122).Itis United States, the reduced lactose content in MPC estimated that, in 2013, 46,000 tons of MPCs have is thought to be beneˆcial in various food applica- been produced in the United States and also 55,000 tions in which browning is undesired or the lactose tons imported2). content should be minimized for nutritional pur- A key process in the manufacturing of MPC is poses. Therefore, MPC is used to replace tradition- al dairy ingredients such as non fat dry milk
Corresponding author: Shinya Ikeda (NFDM) and skim milk powder (SMP) in a num- Department of Food Science, College of Agricultural and Life ber of dairy food applications such as yogurt and Sciences, University of Wisconsin-Madison, 1605 Linden ice cream9～12). Drive, Madison, WI 53706, USA (Tel: ＋16088904877, Fax: ＋16082626872, The caseins in MPC largely retain their original E-mail: sikeda2＠wisc.edu) micellar structure in milk. It has been shown that 2015年 2 月10日受付 2015年 3 月18日受理 the rennet-induced gelation behavior of reconstit- [doi:10.11465/milk.64.127] uted milk prepared using MPC is similar to that of 第巻 skim milk13～16), suggesting that MPC can be used MPCs reconstituted in milk or those reconstituted to standardize milk for eliminating the seasonal in water and then dialyzed against milk33).Further- variability in textural properties of certain types of more, the ˆrmness of the resulting gels was the cheeses to which the addition of MPC is legally largest in the MPC reconstituted in water. It was permitted17～21). Other potential areas of food also found that all of these samples contained simi- applications of MPC include emulsion foods such lar amounts of soluble calcium but the amount of as creams, sauces, and beverages22～27).Ithas caseinomacropeptide (CMP) released from casein been found that oil-in-water emulsions prepared micelles by the action of rennet was the smallest in using MPC as the emulsiˆer can be more stable the MPC reconstituted in water, and hence con- against creaming than those prepared using cluded that the soluble casein component (i.e., sodium caseinates that do not have micellar CMP) had a negative eŠect on rennet coagulation structures22,25). properties of the MPC powders. It is frequently the case that the hydration of EŠects of the protein level in MPC on rennet MPC powders is one of the ˆrst critical steps of gelation behavior were investigated using MPCs the manufacturing of food products containing containing various proportions of protein (i.e., 56, MPC as an ingredient. MPCs show fairly good 70, and 90 on the dry weight basis)14).The solubilities, while signiˆcant decreases in the amount of CMP released increased as the protein solubility may be experienced during storage in level decreased. This was considered to be caused ambient conditions3,28～31). In this review, rennet- by the higher degree of heat-induced denaturation gelation and emulsiˆcation properties of MPC will of proteins in an MPC containing a higher level of be outlined ˆrst, and then the mechanism of the protein. Consistently, the gelation time decreased solubility loss during storage as well as possible with increasing protein level in the MPC approaches to remedy this issue will be discussed. ingredients. This trend was reversed when the DiŠerent deˆnitions of solubility can be found in reconstituted MPCs were dialyzed against skim the articles presented here. Therefore, in this milk. It was considered that changes in the ratio review, the solubility refers to the extent of the between the soluble and colloidal calcium as a dissolution of MPC in a solvent such as water or result from dialysis caused dissociation of casein milk in a broad sense unless otherwise speciˆed. from casein micelles. EŠects of heat treatments of reconstituted Rennet-gelation properties of MPC. MPCs on their rennet gelation behaviors were also investigated13). Heat treatments resulted in a slow- Rennet-induced coagulation of casein is a critical er rate of the increase in the storage modulus, a step in cheese manufacturing, and its outcome is reductioninthegelationtime,andadecreaseinthe dependent on the amount of calcium in the milk yield force required to fracture gels. The reduced serum32). MPCs have lower ratios of soluble salts gelation time was considered to be due to the heat- to the total solids than milk because they are induced aggregation of proteins during heat treat- removed by ˆltration during manufacturing to ments. The decrease in the storage modulus and various degrees. Therefore, the rennet gelation the yield force were related to the extent of the behavior of reconstituted MPCs was compared heat-induced denaturation of whey proteins. with that of raw skim milk15). Reconstituted MPCs MPC powders stored at various temperatures did not coagulate unless they were supplemented ranging from 20 to 50°C showed exponential with approximately 2 mM calcium chloride. The decreases in the solubility over the storage time up addition of a su‹cient amount of calcium ions to 60 days with a greater eŠect at a higher storage restored the coagulation kinetics and gel strength temperature16). It was also found that the ˆnal of the reconstituted MPC to approximately those complex modulus and the yield stress of rennet- of the raw skim milk. In contrast, other studies induced gels containing the aged MPC decreased showed that MPCs reconstituted in water and sup- exponentially with the storage time with a greater plemented with added calcium gelled earlier than eŠect at a higher temperature. The changes in the 第号 solubility of MPC powders during storage correlat- using a dissociating buŠer containing imidazole ed well with their rheological properties. Rennet- and disodium ethylenediaminetetraacetic acid induced gelation is a two phase process consisting (EDTA)23). of the initial phase being the enzymatic hydrolysis Emulsifying properties of 4 diŠerent MPCs of kcasein and the second phase being the aggre- containing various amounts of calcium were gation of the rennet altered casein micelles. investigated25). At a given protein content, the Sodium dodecyl sulfate (SDS)polyacrylamide gel average size of emulsion droplets prepared using electrophoresis (PAGE) patterns of rennet treated the MPCs decreased with decreasing calcium con- MPCs having diŠerent levels of the solubility tent in the MPCs. The surface protein composition showed the presence of almost identical amounts of of the MPC having the largest calcium content was kcasein and parakcasein in all of the samples similar to the protein composition of the casein examined, indicating that the changes in the rheo- micelle in milk, while more ascasein and less b logical properties were related to the second stage casein were found at the droplet surface in the of the rennet-induced gelation. emulsions stabilized using the MPCs having lower calcium contents. The stability of the emulsions Emulsifying properties of MPC prepared using the MPC having the largest calci- um content increased with increasing protein con- Comparative studies on emulsifying properties centration up to 5 w/w, at which the emulsion of various dairy ingredients including MPC were prepared using this MPC was most stable. The conducted22). It was found that the emulsifying stability of the emulsions prepared using the MPCs ability, creaming stability, surface coverage, and having lower calcium contents increased ˆrst with compositions of the interfacial layer of MPC were increasing protein concentration, reached a maxi- similar to those of SMP. The emulsifying abilities mum, and then decreased. Similar trends were of sodium caseinate and whey proteins were simi- observed for emulsions stabilized using sodium lar to each other and greater than those of MPC caseinate. Furthermore, the protein concentration and SMP. The surface coverages of sodium at which the maximum emulsion stability was caseinate and whey proteins were a few mg･m－2, observed decreased with decreasing calcium con- consistent with values typically found for proteins, tent, which coincided with a decrease in the and were approximately 10 times lower than those average particle size of MPC from ca. 180 to 70 nm of MPC and SMP. These results suggest that sig- with decreasing calcium content. These results niˆcantly larger quantities of caseinate and whey suggests that the caseins in the MPC having the protein molecules remained in the aqueous phase largest calcium content largely retained their origi- than MPC and SMP. The creaming stability at a nal micellar structure in milk and that casein relatively large protein content (e.g., ＞5 w/w) micelle structures were disrupted more as more increased in the order of caseinate＜whey protein calcium is removed from the MPCs. ＜SMPMPC. It was therefore considered that MPC was dissolved in water and heated at 90°C the protein molecules that did not adsorb to the for 5 min prior to emulsiˆcation26). The emulsions interface contributed to the depletion-induced thus obtained were further heated at 120°Cfor10 ‰occulation of the emulsion droplets leading to min. The emulsions prepared using the pre-heated enhanced creaming. Additionally, the larger size of MPC showed less heat-induced ‰occulation and the casein micelles in MPC compared to the molec- coalescence of the emulsion droplets than those ules of caseinates or whey proteins may be beneˆ- prepared using unheated MPC. Approximately cial for stabilizing emulsion droplets against cream- 90 of whey proteins were found to have dena- ing since it is known that the free energy of desorp- tured during pre-heating. These denatured whey tion of a particle from the surface is proportional to proteins were considered to be less susceptible to the particle radius squared34). It was also shown the second heat treatment. It was also noted that that the emulsifying ability of MPC was able to be the non-micellar casein fraction might provide improved by disrupting casein micelle structures stabilizing eŠects on the heat-induced aggregation 第巻 of whey proteins during the second heat and permeable to water diŠusion in SMP. The treatment26). It is possible, however, that non- SMP showed excellent rehydration behavior, while micellar casein fractions contribute to the destabili- the rehydration of MPC deteriorated with increas- zation of the emulsion droplets and enhanced ing solid content in the feed solution. The rate of creaming through the depletion ‰occulation solidiˆcation of particle surfaces appeared to be mechanism27). larger in MPC at comparable protein concentra- tions in the feed solution, resulting in larger parti- The solubility of MPC cle sizes in MPC. The chemical composition of the particle surface was determined to be 73 protein, High protein MPCs, particularly those contain- 27 fat, and 0 lactose using X-ray photoelectron ing more than 80 w/w protein, have been report- spectroscopy, suggesting that proteins were in ed to exhibit relatively poor solubilities30,35),which close proximity particularly at the surface of the can further deteriorate during storage at tempera- powder particles. tures above ambient temperatures28,29,36,37) and at The solubility of MPC deteriorated with increas- high moisture content and water activity30,37～40). ing inlet air temperature during spray-drying from The solubility of a high protein MPC containing ca. 77 to 178°C42). The results from gel electrophoresis 83.5 w/w protein decreased signiˆcantly after suggested that the insoluble fraction consisted storage at temperatures between 32 and 45°C, primarily of a, b,andkcaseins. Other studies while the solubility of NFDM remained showed that the insoluble fraction in MPC consist- unchanged28). The solubility of another MPC that ed predominantly of a and bcaseins43).This contained approximately 85 protein on the dry material dissociated in the presence of SDS, weight basis was found to decrease exponentially indicating that it was formed by hydrophobic with time during storage at 20, 30, 35, 40, and 50°C interactions. The presence of disulˆde-linked pro- for up to 60 days, and a master curve was obtained tein aggregates consisting of kcasein, blac- 29) using a time-temperature superposition .The toglobulin, and as2casein were also detected, results from gel electrophoresis indicate that the whiletheywereconsiderednottoplayamajorrole insoluble proteins were caseins but that whey pro- in the formation of the insoluble material. Further- teins remained soluble. The relative humidity was more, the photo-oxidation of MPC induced by UV also shown to have a signiˆcant impact on the solu- radiation resulted in the formation of non-covalent- bility of an MPC containing approximately 80 w/ ly crosslinked high molecular weight aggregates, wprotein37). At a storage temperature of 25°C, the accompanied by a signiˆcant decrease in the solubility of the MPC decreased to 35 after 4 solubility44). weeks when stored at a relative humidity of 84, It was found that a, b,andkcaseins in MPC and to 78 and 70 at a relative humidity of 44 and were lactosylated during storage at 50°C29).After 65, respectively. The solubility of an MPC con- 3 days of storage at 50°C, lactosylated species taining ca. 85 w/wproteinwasalsofoundto having two lactose groups attached were detected. decrease during storage at 25°Cto48and30 at a No further changes in the degree of lactosylation water activity of 0.45 and 0.85, respectively40). were observed after several days of storage. It was then speculated that the insolubility of MPC was Mechanisms of the reduction in the solubility caused by crosslinking of proteins at the surface of the powder particles. To seek the correlation The process of the particle formation during between the solubility and the degree of the Mail- spray-drying of MPC was shown to diŠer from lard reaction, eŠects of the addition of glucose or that of SMP41). At relatively low moisture contents lactose to an MPC containing 80 w/wproteinon (＜0.6 kg/kg), more energy was required to its solubility were investigated37). The rate of the remove the same quantity of water from SMP than Maillard reaction increased more signiˆcantly by MPC. This was considered to be due to the forma- the addition of glucose than lactose. In contrast, tion of outer skins or crusts that were less porous the solubility decreased more signiˆcantly by the 第号 addition of glucose than lactose, suggesting that of the disruption of agglomerated particles into the Maillard reaction was indeed a cause of the primary powder particles and the simultaneous solubility loss in the MPC. Advanced Maillard release of materials from the powder particles into reaction products such as methylglyoxal or the surrounding aqueous medium49).Therate- dehydroalanine were considered to crosslink pro- limiting step of the rehydration of MPC appeared teins and hence reduce the solubility of MPC45). to be the second process, which was accelerated by
Dephosphorylation of as1casein that was expected an increase of the solvent temperature. Further- to decrease the formation of dehydroalanine did more, non-micellar components such as whey pro- not prevent the formation of crosslinks between tein, lactose, sodium, and potassium were shown to proteins, indicating that dehydroalanine was not be released rapidly during rehydration, while involved in the crosslinking process. In contrast, micellar components such as caseins, calcium, the addition of lactose or methylglyoxal enhanced phosphorus, and magnesium were released slowly 50) the crosslinking of as1casein considerably, con- with storage slowing the release process further . ˆrming a possible pathway of protein crosslinking It was considered that the penetration of water into in MPC involving advanced Maillard reaction the powder particle was not a rate-limiting factor products. because much larger molecules such as whey pro- The structural integrity of the casein micelle is teins and lactose were easily released out of the maintained in MPC46), while conformational powder structure. modiˆcations of caseins appear to be involved Electron-microscopy studies on the surface mor- in the mechanisms of the solubility loss of phology of rehydrated fresh MPCs revealed a MPC35,40,47,48). The principal component analysis porous gel-like structure that restrained the release revealed good correlations between the solubility of individual casein micelles into the surrounding and Fourier transform infrared (FTIR) spectra of liquid without preventing water penetration and MPC35,47). MPCs stored at various water activities the solubilization of non-micellar components, (0.00.85) and temperatures (25 and 45°C) for up resulting from a combination of diŠerent types of to 12 weeks showed signiˆcant decreases in the physical interactions between casein micelles such solubility with aging, and this process was as bridging and direct contact51).Duringstorage, enhanced by increasing water activity and storage increased interactions between casein micelles temperature40,48). Minor changes in the secondary appeared to occur, leading to the formation of a structure of protein were observed in FTIR spec- monolayer skin of fused casein micelles. Under- tra, indicating a certain degree of unfolding of pro- neath the skin layer, a more open and porous struc- tein molecules. The results from nuclear magnetic ture similar to that of the fresh MPC particle sur- resonance (NMR) relaxometry showed the face can be seen in micrographs, indicating that the presence of three distinct populations of water casein micelles that were not involved in the forma- molecules, the signal intensities of which varied tion of the skin layer were also di‹cult to be with water activities and temperatures during released into the surrounding liquid medium. X storage. These results suggest that the storage at a ray photoelectron spectroscopy analysis on the high water activity result in more water molecules bonding state of proteins in the near-surface region in close proximity to the protein surface as well as indicated an increase in non-polar bonds, which more enhanced unfolding of proteins, leading to a was associated with an increase in the hydropho- reduced solubility of MPC. bicity at the surface52). Studies on the kinetics of the rehydration of MPC suggested that the low solubility of a high- Approaches to improve the solubility. protein MPC was a consequence of slow dissolu- tion kinetics rather than the formation of insoluble The solubility of MPC can be improved by materials in the course of storage49,50).The manipulating the method of rehydration. It is a rehydration process of the high-protein MPC was common practice to rehydrate MPC at elevated shown to occur in two overlapping steps consisting temperatures up to 60°C to ensure its proper 第巻 hydration13～15,49,53). The average particle size of an dered to be due to the disruption of aggregates MPC containing 90 w/w protein was determined between whey proteins and caseins prior to spray- to be greater than 40 mm after being dispersed in drying. The sonication prior to spray-drying was water and stirred for 30 min at 20°C, while it also found to be beneˆcial for improving functional decreased to less than 1 mm after being stirred for properties of MPC such as gelation and emul- 30 min at 60°C14). The incubation of the same MPC sifying properties57). The solubility increased sig- at 60°C for 30 min without the application of niˆcantly from ca. 36 to 88 after 5 min of soni- mechanical agitation resulted in an average parti- cation preceding spray-drying, which was accom- cle size greater than 40 mm. panied by an increase in the surface hydrophobicity The ultrasonication of aqueous dispersion of a from ca. 178 to 417, an increase in the emulsifying fresh MPC containing 81.4 w/w protein for 30 activity index from ca. 4.3 to 6.2, and an increase in sec at an energy density of 10.5 J･mL－1 was found the storage modulus of rennet gels from ca. 10 to to be capable of reducing the particle size to a value 30 Pa. Scanning electron microscopy images similar to that obtained by conventional stirring revealed that small particles were formed and they using a 3bladed propeller for 90 min54).Further were trapped in dents on the surface of large parti- sonication had little additional eŠect on the reduc- cles. The results from SDSPAGE conˆrmed the tionintheparticlesize.Theultrasonicationwas absence of signiˆcant changes in the molecular considered to create cavitation that caused local- weights of these proteins. ized turbulent ‰ows and sudden changes in pres- Micro‰uidization is another high shear technique sures that facilitated the breaking up of agglomer- typically used for the preparation of ˆne emulsions. ated particles but also generated heat. The heat MPCs were either homogenized, micro‰uidized, or had to be dissipated to prevent the heat-denatura- sonicated prior to spray-drying and stored at 22°C tion and aggregation of whey proteins that would for 8 months58). The solubilities of the control, then lead to a decrease in the solubility. In separate homogenized, micro‰uidized, and sonicated MPCs studies, the rate of hydration of a low solubility were found to decrease to 51, 59, 69, and 55, MPC was determined during various high shear respectively. These results were considered to be treatments such as ultrasonication, high pressure due to disintegration of protein components by homogenization, and high-shear rotor-stator high shear treatments, causing the formation of mixing and compared to low-shear overhead surface active fragments of proteins. Such surface stirring55). All of the examined high shear treat- active protein fragments are likely to competitively ments greatly accelerated the solubilization of the adsorb to the air-water interface during spray- MPC by physically breaking apart the powder drying and alter the surface composition of result- agglomerates and accelerating the release of ing powder particles. individual casein micelles into solution. The The application of static high pressure to milk is average particle size reduced to 1.1 mmbythe expected to cause various changes in milk compo- application of ultrasonication for 5 min. The high nents, including an increase in pH and calcium pressure homogenization at 80 and 120 bar result- activity, the denaturation of whey proteins, and a ed in particle sizes of 1.3 and 1.2 mm, respectively. disruption of casein micelle structures and colloidal Attempts have been made to improve the solubil- calcium phosphate (CCP)59). The solubility of ity of MPC by modifying its manufacturing fresh MPC powders prepared without the applica- processes. MPCs sonicated prior to spray-drying tion of high pressure was determined to be 66, maintained their solubilities better than un-sonicat- and decreased to less than 50 of its initial value ed MPCs during storage at 25°Candrelative after 12 months of storage at ambient tempera- humidities of 23 and 76 for up to 60 days56).The tures59). In contrast, the solubility of fresh MPC solubility of the un-sonicated MPC decreased to ca. powders prepared with the application of a high 50 by storage at a relative humidity of 76 for pressure of 200 MPa prior to spray-drying was 60 days, while that of the sonicated MPC showed a 85, and decrease to 85 of its initial value after solubility of 75 after the storage. This was consi- 12 months of storage at ambient temperatures. 第号
The improved solubility was attributed to an the addition of 0150 mM NaCl62). altered surface composition of the powder particle The removal of CCP appeared to increase elec- arising from an increased concentration of non- trostatic repulsive forces between casein micelles, micellar casein in the milk due to the application of resulting in better hydration properties of CCP high pressures prior to drying. depleted MPCs43). The solubilization of CCP may EŠects of nanoˆltration prior to spray-drying on also aŠect the structural organization of protein the solubility of MPC powders were compared particles and consequently hydration properties of with those of evaporation60). The nanoˆltration of MPC63). The eŠect of the acidiˆcation of milk by milk resulted in a reduced free sulfhydryl content the addition of gluconodlactone (GDL) prior to and decreased surface hydrophobicity, indicating ultraˆltration was therefore investigated63).The the formation of disulˆde bonds and hydrophobic acidiˆcation resulted in pH of 6.0, accompanied by interactions between casein micelles. However, the a signiˆcant decrease in the total calcium content, insolubility index of the MPC prepared from the but insigniˆcant eŠects on the proximate composi- evaporated milk was signiˆcantly larger than that tion, particle size, particle density, and microstruc- of the MPC prepared from the nanoˆltered milk, ture. The calcium-depleted MPC was more soluble which might be attributed to the lower operation than the control MPC. These results suggested temperature during the nanoˆltration. that the acidiˆcation to pH 6.0 reduced protein- The solubility of MPC was found to have a sig- protein interactions during drying that would con- niˆcant positive correlation with its sodium content tribute to a decrease in the solubility of MPC. and lower calcium, magnesium, and phosphorus contents35). The impact of the addition of salts dur- Conclusions ing diaˆltration was also investigated61,62).The control MPC without any added salts showed a High contents of protein, low contents of lactose, solubility of 53, while MPCs prepared with the well-preserved casein micelle structures, and addition of sodium chloride or potassium chloride largely un-denatured whey proteins make MPCs were 100 soluble61). Furthermore, lower protein versatile functional ingredients for various food and calcium contents were observed in the super- applications. MPCs are particularly suitable for the natants of reconstituted and ultracentrifuged sam- standardization of cheese milk and the stabilization ples of the control MPC as compared to those of of oil-in-water emulsions due to their excellent the MPCs with added salts. These results suggest- rennet gelation and emulsion stabilizing properties. ed that the addition of salts impacted the distribu- The mechanism of the development of the tion of minerals and proteins in the colloidal and insolubility of MPC during storage at an elevated serum phases. The addition of salts increases the temperature and/or a relatively high humidity has ionic strength and hence reduces the activity not been fully understood. A plausible explanation coe‹cients of ions, leading an increase in the solu- is that at a relatively high humidity, water molec- bility of ions. The addition of salts is thus expected ules adsorbed to a protein molecule form multiple to increase the amount of soluble calcium and inor- layers that enable conformational changes of the ganic phosphate, and in turn, loosen the structure protein. Such conformational changes may lead of the casein micelle31).Theadditionofsaltsisalso to more enhanced intermolecular interactions expected to reduce electrostatic repulsive forces between proteins and hence a reduced solubility. between casein micelles. MPC powders prepared Continuing eŠorts for weakening protein-protein by the addition of 150 mM NaCl during the interactions in MPCs are being made by modifying diaˆltration process showed the highest solubility, the manufacturing process of MPC. In practice, the highest 1(anilino)naphthalene8sulfonate the hydration of MPC at an elevated temperature (ANS)based surface hydrophobicity, the lowest up to 60°C with the application of high shear is 6propionyl2(N, Ndimethylamino)naphthalene recommended to ensure su‹cient hydration of (PRODAN)based surface hydrophobicity, and MPC for food applications. the least aggregate formation in those prepared by 第巻
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乳タンパク質濃縮物（MPC）の機能性と水和性
池田新矢 （ウィスコンシン大学マディソン校食品科学科 1605 Linden Drive, Madison, WI 53706, USA）
乳タンパク質濃縮物（MPC）は限外ろ過，透析ろ過等の膜分離プロセスとそれに続く噴霧乾燥を経て製造される乾 燥乳タンパク質粉末である。その優れた栄養性と物理化学的機能性により，MPC はタンパク質の摂取量を高めること を目的とした栄養食品や飲料，あるいはチーズ，ヨーグルト，アイスクリーム等の乳製品等，様々な食品の原料として 広く認識されるようになってきた。本総説では，MPC の機能性と水和性について，特にレンネットゲル化性，水中油 滴型エマルションの安定化，保存時の水溶性の低下現象，および水溶性を向上するための手法に焦点を当てて解説す る。また，脱脂粉乳（NFDM/SMP）やカゼイネート等，他の乳タンパク質原料と MPC の機能性の類似点および相違 点を比較する。さらに，保存時の温度や湿度が水溶性の低下の度合いに与える影響およびその機構について論じる。