Functional and Hydration Properties of Milk Protein Concentrate (MPC)
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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.