Mechanism Of Solubility Decreasing Of Milk Protein Concentrate During Storage

Milk Protein Concentrate is a kind of powder products with high proteincontent extracted from bovine milk, which is always used as ingredient in foodindustry. However, the solubility of MPC will gradually decrease during the storageperiod which limits its application to some extent in food industry. The study chosecommercially available MPC as raw material and MPC containing different proteinlevels and sugars was prepared by dialyzing commercially available MPC. Changesin solubility of MPC, protein cross-linking and Maillard reaction were observed.And then mechanism of solubility decreasing of MPC during storage wasilluminated. In addition, this article investigated whether ultrasonic technologycould improve solubility or not. The principal contents and results were concludedas followed:This study chose commercially available MPC as experimental materials andeffects of different blending time, centrifuge force and time interval on solubility ofmilk protein concentrate were studied in this work. Based on experimental resultsand materials, solubility was determined at these parameters: blending time was10min, centrifuge force was2400g and time interval was0min. MPC with differentprotein levels and MPC with different sugars was prepared by dialyzing, then theseMPC were stored at50℃for15d,30d and45d for latter determination. Theresults showed that solubility of MPC decreased during storage and solubility ofMPC70and MPC77(content of sugar is7%) was40.68%and13.02%respectivelywhen stored for45d.By analysing soluble protein content, denaturing and native polyacrylamide gelelectrophoresis to find the relationship between lower solubility and protein. Theresults proved that protein cross-linking was a main reason for lower solubility andprotein interacted with others by hydrogen bond, disulfide bond, hydrophobicinteraction and covalent bond. By analysing color difference, pH and free aminogroups of MPC containg different sugars, this research could state the relationshipbetween lower solubility and Maillard. The results illustrated that Maillard reactionwas also a reason for lower solubility during storage. A small amount of sugar in theMPC reacted with protein or amino acid with free amino, this process formedproduct promoting protein cross-linking. Maillard reaction was influenced byprotein cross-linking. However, protein cross-linking influnced maillard reaction,the greater cross-linking, the slower Maillard reaction.This article was to compare the effect of ultrasonic technology on different stored MPC, we could use ultrasonic technology to improve MPC’s solubility beforedrying.The research provided mechanism for poor solubility in storing MPC andtheoretical basis for developing MPC with stable solubility.