Formation of volatile compounds in whey protein concentrate during elevated temperature storage as a function of water activity

Abstract

Abstract The formation of volatile compounds in a 75% commercial whey protein concentrate (WPC) during 6 days of elevated temperature storage at 60 °C in the dark and at water activity (a w ) values ranging from 0.11 to 0.79 was investigated by dynamic headspace analysis (DHA). WPC samples were stored in 125 mL serum bottles which functioned as combination a w control containers and external DHA sampling devices. Formation of major volatile compounds, i.e., aldehydes, ketones.furans, aromatic hydrocarbons and sulfur-containing compounds, was strongly influenced by a w . Combined total ion chromatogram (TIC) peak areas for all volatile compounds recovered from nonstored WPC was 45 × 10 6 and values ranged from 1089 × 10 6 to 6135 × 10 6 arbitrary units for WPC stored at a w 0.11 and 0.79, respectively. The concentrations of key volatile compounds were increased dramatically as a result of storage at the elevated temperature. For example, hexanal, an important lipid oxidation product, increased from about 11 ng g −1 nonstored WPC to about 1430 ng g −1 WPC stored at 0.79 a w . Dimethyl disulfide was increased from a nondetectable concentration for nonstored WPC to over 2300 ng g −1 WPC stored at 0.79 a w . Other key compounds that exhibited major increases in concentration during storage were 2-butanone, benzene and 1,3-dimethyl benzene. These results confirm that a w is an important factor for controlling storage stability of WPC and that DHA is a rapid, reliable, and highly sensitive method for monitoring storage stability of WPC.