Dry heat treatment of skim milk powder greatly improves the heat stability of recombined evaporated milk emulsions

In this study, skim milk powder (SMP) was subjected to a controlled dry heat treatment at 60 degrees C and relative humidity of 74% to improve the heat stability of recombined evaporated milk (REM) emulsions. Free amino group determination and SDS-PAGE analysis confirmed that the glycation of both whey proteins (WP) and caseins with lactose mainly occurred in the early period (< 8 h). An increase in surface hydrophobicity and changes in the structure of the SMP proteins by circular dichroism (CD) and FT-IR were found after a long time of incubation (> 16 h). The non-sedimentable protein analysis indicated that WP-casein interaction and casein micelle dissociation happened during (prolonged) dry heating. The heat stability of REM emulsions stabilized by dry heated SMP was greatly improved: dry-heated SMP-stabilized REM emulsions could withstand at least 30 min of heating at 120 degrees C without significant increase in particle size and viscosity (P > 0.05). However, excessive dry heating (>20 h) adversely affected the reconstitution ability of SMP as well as the heat stability of REM emulsions.