Stabilization of Protein by Lactose during Storage in the MPC 85 System

Abstract

Milk protein is the most valuable component and its stability is important during processing and storage. The stabilization is influenced by moisture and position of milk powder. It is assumed that lactose can acts as stabilizer of protein (protect from protein unfolding). The phenomenon of this stabilization was studied at three water activity (aw 0.23,0.54 and 0.75), with low concentration of lactose addition (5, 15 and 30%) during 6 weeks. Sample preparation'of MPC powders and equilibration at different relative humidity was conducted before storage. Analysis of MPC to investigate the influence of lactose in protein stabilization include solubility test, glass transition (Tg) by TMCT (Thermal Mechanical Compression Test), secondary protein structure (FTIR), and T2 relaxation (NMR) to measure the protein water interaction in MPC85 system. The role of lactose to retain the change of stability during storage can be observed clearly at aw 0.54. In this condition, the rate of solubility and Tg decreasing/week and also the rate of increasing of T2 short proportion/week can be retained by lactose adding. The capability of lactose to retain the rate of change of solubility, Tg and T2 short proportion cannot be observed at low water activity (aw 0.23) because of the small amount of water in the system. At aw 0.75, lactose adding c annot retain the change of stability due to very higher water content and lactose coystallization. Evidence from FTIR suggested that this reduction in solubility was not directly linked to major conformational changes within protein structures.