Abstract #M13

# M13
Dry heat treatment affects solubility, whey protein denaturation, and soluble aggregates formation in nonfat dry milk.
K. S. Alán1, K. Schmidt*1, 1Kansas State University, Manhattan, KS.

Heat treatments are used in the dairy industry to ensure microbiologically safe products, extend shelf life, and improve functional properties. Dependent upon temperature and time, these treatments can cause protein denaturation, whey protein aggregation as well as initiate the Maillard reaction in liquid milk systems. However, insufficient evidence exists about the impact of a dry heat treatment in a dry milk system, such as nonfat dry milk (NDM). The aim of this research was to apply a dry heat treatment to low heat (LH) NDM to elucidate the effect of the dry heat on proteins. Radiofrequency dielectric heat was the mechanism bring LH-NDM to 1 of 3 temperatures: 80, 85, and 90°C and all samples were held at that temperature for 90 min. LH-NDM and high heat (HH) NDM that were not dry-heated were included in the assessments. All samples were evaluated for whey protein nitrogen index (WPNI), solubility (NSI), XTT reduction (Maillard reaction) and soluble aggregates content. One-way ANOVA was used to determine differences among the 5 samples, with significant means differentiated with the Tukey’s test (P ≤ 0.05). Results showed that LH-NDM treated at 85°C had similar content of soluble whey protein aggregates as HH-NDM, further these samples contained significantly more soluble aggregates than did the LH-NDM at 80°C, and 90°C. The WPNI for HH-NDM was significantly less than the 4 LH-NDM samples, regardless of dry heat treatment. The WPNI decreased in all dry-heated LH-NDM samples when compared with non-treated LH-NDM (2% at 80°C, 7% at 85°C and 15% at 90°C). LH-NDM treated at 80°C maintained good solubility; however, LH-NDM treated at 85°C and 90°C had losses in solubility (0.64% and 3.34%, respectively) when compared with LH-NDM. Results from the XTT test indicated that the Maillard reaction products were greater in the HH-NDM, LH-NDM treated at 85°C and 90°C. These results suggest that dry heat treatment can affect the proteins and their interactions in LH-NDM. It is important to understand the effects of dry heat in dairy powders, as these treatments could provide ideal conditions to improve the functional properties of NDM.

Key Words: nonfat dry milk, milk proteins, dry heat treatment