Effect of dry heat treatment temperature of skim milk powder on the improved heat stability of recombined filled evaporated milk

Abstract

The incubation temperature is known to play an important role in the Maillard reaction and protein cross-linking during dry heat treatment of protein-sugar mixtures. In this study, dry heating of skim milk powder (SMP) at various incubation temperatures from 60 to 80 °C was investigated. The effect of this SMP pretreatment on the heat stability of the derived recombined filled evaporated milk (RFEM) was evaluated via particle size analyses and viscosity measurements, which showed that the required incubation time to obtain an optimal heat stability was greatly shortened with increasing dry-heat incubation temperature: whereas 8 h of dry heat incubation was needed at 60 °C, 2 h at 70 °C, and 1 h at 80 °C were sufficient to obtain a heat stable SMP, respectively. This effect was thought to be due to the fact that elevated incubation temperatures accelerated glycation between lactose and milk proteins, as indicated by free amino group content analysis and SDS-PAGE. However, SMP subjected to excessive incubation failed to maintain the original droplet diameter and viscosity after heating and showed a poor heat stability. PCA and correlation analysis results suggested that the solubility of the dry heated SMP and the heat stability of the derived RFEM were both correlated to the sulfhydryl content and carbonyl content (R > 0.6). Overall, the kinetic study of the protein carbonyl content, the sulfhydryl content and the degree of glycation elucidated the remarkable influence of dry heat incubation temperature on the SMP properties and offered a valuable tool for optimizing the SMP functional properties.