FORMATION OF VOLATILE COMPOUNDS IN WHEY-PROTEIN CONCENTRATE DURING ELEVATED-TEMPERATURE STORAGE AS A FUNCTION OF WATER ACTIVITY

The formation of volatile compounds in a 75% commercial whey protein c oncentrate (WPC) during 6 days of elevated temperature storage at 60 d egrees 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 mt serum bottles which functioned as combi nation a(w) control containers and external DHA sampling devices. Form ation of major volatile compounds, i.e., aldehydes, ketones, furans, a romatic hydrocarbons and sulfur-containing compounds, was strongly inf luenced by a(w). Combined total ion chromatogram (TIC) peak areas for all volatile compounds recovered from nonstored WPC was 45 x 10(6) and values ranged from 1089 x 10(6) to 6135 x 10(6) arbitrary units for W PC stored at a(w) 0.11 and 0.79, respectively. The concentrations of k ey volatile compounds were increased dramatically as a result of stora ge at the elevated temperature. For example, hexanal, an important lip id oxidation product, increased from about 11 ng g(-1) nonstored WPC t o 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 exhib ited major increases in concentration during storage were 2-butanone, benzene and 1,3-dimethyl benzene. These results confirm that a(w) is a n important factor for controlling storage stability of WPC and that D HA is a rapid, reliable, and highly sensitive method for monitoring st orage stability of WPC. (C) 1996 Elsevier Science Limited