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Ultrafiltration and diafiltration of skim milk altered delicate salt equilibrium and composition of 59 UF retentate (59 UFR), and thus adversely affected the reconstitutional and functional properties of milk protein concentrate (MPC) powders. It might be due to interaction and aggregation of proteins during spray drying. Therefore, this study was envisaged to investigate the effect of disodium phosphate (DSP) addition, diafiltration and homogenization of retentates on physico-chemical, functional and rheological properties of MPC60 powders. Solubility of fresh control powder was significantly lower than MPC60-H powder; at par with that of MPC60-DSP and MPC60-Na-K, but remained minimum after 60 days of storage at 25 ± 1°C. The pH (6.6) adjustment of 59 UFR with DSP, significantly enhanced the dispersability, wettability, specific surface area (SSA), heat coagulation time (HCT), emulsification capacity and stability; buffer index of MPC60-DSP powder over control. Diafiltration of 59 UFR with NaCl and KCl, significantly (P \ 0.05) decreased calcium content, but enhanced pH and mineral content of MPC60-Na-K powder. This treatment led to significant improvement in dispersability, SSA, emulsification capacity and stability, HCT and oil binding properties. Flowability, wettability, dispersability, HCT, foaming capacity, emulsification capacity and stability were also improved significantly in MPC60-H powder made from homogenized 59 UFR. Rheological behavior of reconstituted powder samples exhibited pseudoplastic behavior, best explained by Hershel Bulkley model. These MPC60 powders with improved functional properties can be used for the improvement of quality attributes of various food formulations.

Poor solubility of milk protein concentrates (MPCs) is a key deterrent factor in their wider applications in the food industry as compared to other protein-rich dried products such as casein, caseinates and whey protein concentrates and isolates. Apart from the processing factors, the protein content of a MPC also decides its solubility. Solubility is a pre-requisite property of MPCs on which its other functional properties are majorly depended. Further, there is a confusion about the term MPC itself in the literature. An attempt has been made to describe MPC and provide an understanding on the manufacture of MPCs. Further, mechanisms of insolubility, factors affecting solubility of MPCs and an insight into the recently evolved strategies for overcoming the challenges related to their poor heat stability and solubility have been reviewed. Potential applications of MPC to be utilized as a novel ingredient in food industry are also outlined.

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Ultrafiltration (UF) of skimmed milk altered the composition of UF retentate and decreased the heat stability. Heat stability further reduced upon its subsequent homogenization or diafiltration. Poor heat stability of UF retentate restricts its processing at elevated temperatures. Therefore, this study was aimed to investigate the effect of protein concentration, homogenization and addition of stabilizing salts on the heat stability and rheological properties of UF retentates. Changes in the heat stability of fivefold homogenized UF retentate (59 HUFR) was studied in the pH range of 6.1-7.0. Disodium phosphate and trisodium citrate significantly increased the heat coagulation time (HCT) from 1.45 min (pH 6.41) to 120 min (at pH 6.5, 6.6, 7.0) and 80 min (pH 6.6), respectively. Significant reduction in f-potential of UF retentates was observed with an increase in calcium and reduction in pH during UF process. Rheological behaviour of retentates above threefold concentration exhibited Herschel-Bulkley behavior with linear increase in flow behavior index (n). Changes in the viscosity of the homogenized retentates were measured at the respective pH of maximum heat stability as a function of temperature (20-80°C). Promising approaches that might improve the heat stability, solubility and other functional properties of protein rich powders have been discussed in this article.