Effect of pre-drying thermal treatment on commercial dried milk powder protein technofunctionality

M Lokre, R Owusu-Apenten, R Roberts, G Ziegler

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

The properties of nonfat dried milk powder (NDM), a multifunctional ingredient for the food industry, are intimately linked to the extent of heating before drying. Commercial NDM are classified depending on the extent of heat pre-treatment as high-heat (HH), medium heat (MH) or low heat (LH). The effect of heat treatment of fluid milk proteins has been extensively studied. However, the effect of pre-drying heat treatment on NDM protein functionality is poorly understood. The aim of this study was to determine the effect of pre-drying thermal treatment on NDM protein technofunctionality. Total and free sulfhydryl content of the LH-NDM and HH-NDM powders was determined with the Ellman's assay. Casein and whey protein fractions were isolated from commercial LH-NDM and HH-NDM by ammonium sulfate precipitation and then subjected to physicochemical analysis for lysine concentration, surface hydrophobicity, nominal molecular weight by sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE), and denaturation extent by differential scanning calorimetry (DSC). Finally, techno-functionality of LH-NDM and HH-NDM was compared by oscillatory rheology of d-glucono-lactose (GDL) induced gels. NDM total sulfhydryl content (micromoles/g) did not change with different heat pre-treatment (2.6 ± 0.9 for LH and 2.5 ± 0.11 for HH). The exposed SH content however, showed significant differences with high values for HH-NDM (0.91±0.03 for LH and 1.3±0.04 for HH). Physiochemical analysis of the casein and whey protein fractions obtained showed an increase in surface hydrophobicity and denaturation extent (DSC and SDS-PAGE) and a decrease in lysine concentration with higher heat treatment. Rheological analysis demonstrated that the gels from HH-NDM had a higher G' value (109.4 Pa) as compared to the LH-NDM (23.1 Pa). The HH-NDM also showed a greater stability against aging effects. These results suggest that the pre-drying heat treatment greatly affects the characteristics and technofunctionality of NDM proteins
Original languageEnglish
Title of host publicationUnknown Host Publication
PublisherInstitute of Food Technologists
Number of pages1
Publication statusPublished - 2005
Event2005 IFT Annual Meeting, July 16 - 20; New Orleans, LA - New Oleans
Duration: 1 Jan 2005 → …

Conference

Conference2005 IFT Annual Meeting, July 16 - 20; New Orleans, LA
Period1/01/05 → …

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    Lokre, M., Owusu-Apenten, R., Roberts, R., & Ziegler, G. (2005). Effect of pre-drying thermal treatment on commercial dried milk powder protein technofunctionality. In Unknown Host Publication Institute of Food Technologists.