Effect of water content on glass transition and protein aggregation of whey protein powders during short-term storage

Peng Zhou, Theodore P. Labuza

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The objectives of this study were to investigate the moisture-induced protein aggregation of whey protein powders and to elucidate the relationship of protein stability with respect to water content and glass transition. Three whey protein powder types were studied: whey protein isolate (WPI), whey protein hydrolysates (WPH), and beta-lactoglobulin (BLG). The water sorption isotherms were determined at 23 and 45°C, and they fit the Guggenheim-Andersson-DeBoer (GAB) model well. Glass transition was determined by differential scanning calorimeter (DSC). The heat capacity changes of WPI and BLG during glass transition were small (0.1 to 0.2 Jg -1 °C -1), and the glass transition temperature (T g) could not be detected for all samples. An increase in water content in the range of 7 to 16% caused a decrease in T g from 119 down to 75°C for WPI, and a decrease from 93 to 47°C for WPH. Protein aggregation after 2 weeks' storage was measured by the increase in insoluble aggregates and change in soluble protein fractions. For WPI and BLG, no protein aggregation was observed over the range of 0 to 85% RH, whereas for WPH, ∼ 50% of proteins became insoluble after storage at 23°C and 85% RH or at 45°C and ∼ 73% RH, caused mainly by the formation of intermolecular disulfide bonds. This suggests that, at increased water content, a decrease in the T g of whey protein powders results in a dramatic increase in the mobility of protein molecules, leading to protein aggregation in short-term storage.

Original languageEnglish (US)
Pages (from-to)108-116
Number of pages9
JournalFood Biophysics
Issue number2-3
StatePublished - Sep 1 2007


  • Disulfide bond
  • Glass transition
  • Hydrolysates
  • Protein aggregation
  • Water
  • Whey proteins

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