Flavor and Odor Defects of Gamma-Irradiated Skimmilk. I. Preliminary Observations and the Role of Volatile Carbonyl Compounds1,2

Abstract

Summary To gain insight into the radiation-induced flavor and odor problem of skimmilk, the effects of ionizing (gamma) radiations at two dosages, 2×10 6 and 5×10 6 rep, on skimmilk and certain of its fractions were studied. Among the effects noted were fragmentation and aggregation of the proteins, activation of sulfhydryl groups, lowering of pH, and an increase in titratable acidity, browning, and the production of off-flavor and odor compounds. All of these changes were intensified at the 5×10 6 rep level of radiation. Of the volatile carbonyl compounds produced in skimmilk by radiation, acetaldehyde seems to be the only one of flavor significance (malty). The principal radiation-induced off-flavor appears to arise from a group of potent, disagreeable-smelling sulfur compounds. Methyl mercaptan, methyl sulfide, and methyl disulfide are postulated as dominant members of this group. These compounds originate primarily from the milk protein (casein). Radiation of aqueous lactose solutions produced acids which, outside of sourness, had no flavor or odor.