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 contributionpeer-review


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 (in print/issue) - 2005
Event2005 IFT Annual Meeting, July 16 - 20; New Orleans, LA - New Oleans
Duration: 1 Jan 2005 → …


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


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