Insolubility in milk protein concentrates: potential causes and strategies to minimize its occurrence

Milk protein concentrates (MPCs), which are produced from skim milk following a series of manufacturing steps including pasteurization, membrane filtration, evaporation and spray drying, represent a relatively new category of dairy ingredients. MPC powders mainly comprise caseins and whey proteins in the same ratio of occurrence as in milk. While bovine MPCs have applications as an ingredient in several protein enriched food products, technofunctional concerns, e.g., reduced solubility and emulsification properties, especially after long-term storage, limit their widespread and consistent utilization in many food products. Changes in the surface and internal structure of MPC powder particles during manufacture and storage occur via casein-casein and casein-whey protein interactions and also via the formation of casein crosslinks in the presence of calcium ions which are associated with diminishment of MPCs functional properties. The aggregation of micellar caseins as a result of these interactions has been considered as the main cause of insolubility in MPCs. In addition, the occurrence of lactose-protein interactions as a result of the promotion of the Maillard reaction mainly during storage of MPC may lead to greater insolubility. This review focuses on the solubility of MPC with an emphasis on understanding the factors involved in its insolubility along with approaches which may be employed to overcome MPC insolubility. Several strategies have been developed based on manipulation of the manufacturing process, along with composition, physical, chemical and enzymatic modifications to overcome MPC insolubility. Despite many advances, dairy ingredient manufacturers are still investigating technical solutions to resolve the insolubility issues associated with the large-scale manufacture of MPC.

Updating insights into the rehydration of dairy-based powder and the achievement of functionality

Dairy-based powder had considerable development in the recent decade. Meanwhile, the increased variety of dairy-based powder led to the complex difficulties of rehydrating dairy-based powder, which could be the poor wetting or dissolution of powder. To solve these various difficulties, previous studies investigated the rehydration of powder by mechanical and chemical methods on facilitating rehydration, while strategies were designed to improve the rate-limiting rehydration steps of different powder. In this review, special emphasis is paid to the surface and structure of the dairy-based powder, which was accountable for understanding rehydration and the rate-limiting step. Besides, the advantage and disadvantage of methods employed in rehydration were described and compared. The achievement of the powder functionality was finally discussed and correlated with the rehydration methods. It was found that the surface and structure of dairy-based powder were decided by the components and production of powder. Post-drying methods like agglomeration and coating can tailor the surface and structure of powder afterwards to obtain better rehydration. The merit of the mechanical method is that it can be applied to rehydrate dairy-based powder without any addition of chemicals. Regarding chemical methods, calcium chelation is proved to be an effective chemical in rehydration casein-based powder.

Thermal and Mineral Sensitivity of Oil-in-Water Emulsions Stabilised using Lentil Proteins

Oil-in-water emulsion systems formulated with plant proteins are of increasing interest to food researchers and industry due to benefits associated with cost-effectiveness, sustainability and animal well-being. The aim of this study was to understand how the stability of complex model emulsions formulated using lentil proteins are influenced by calcium fortification (0 to 10 mM CaCl2) and thermal processing (95 or 140 °C). A valve homogeniser, operating at first and second stage pressures of 15 and 3 MPa, was used to prepare emulsions. On heating at 140 °C, the heat coagulation time (pH 6.8) for the emulsions was successively reduced from 4.80 to 0.40 min with increasing CaCl2 concentration from 0 to 10 mM, respectively. Correspondingly, the sample with the highest CaCl2 addition level developed the highest viscosity during heating (95 °C × 30 s), reaching a final value of 163 mPa·s. This was attributed to calcium-mediated interactions of lentil proteins, as confirmed by the increase in the mean particle diameter (D[4,3]) to 36.5 µm for the sample with 6 mM CaCl2, compared to the unheated and heated control with D[4,3] values of 0.75 and 0.68 µm, respectively. This study demonstrated that the combination of calcium and heat promoted the aggregation of lentil proteins in concentrated emulsions.