CHEMICAL CHARACTERIZATION OF RAW-MILK SAMPLES WITH AND WITHOUT OXIDATIVE OFF-FLAVOR

Milk samples with and without oxidized flavor were obtained from two d ifferent commercial dairy herds. Milk components that are important fo r the susceptibility of milk fat to spontaneous oxidation, (i.e., fatt y acid composition and the concentrations of alpha-tocopherol, beta-ca rotene, and ascorbic acid) were analyzed to describe the variation in the susceptibility of milk fat to oxidation in raw milk. The samples w ere also analyzed using dynamic headspace gas chromatography to determ ine volatile oxidation products, primarily straight-chain aldehydes. T he results showed that milk samples exhibiting off-flavor had higher l inoleic acid content in the neutral fat fraction. At one farm, the con centrations of both alpha-tocopherol and beta-carotene were lower in s amples that demonstrated off-flavor. At the other farm, this differenc e was not statistically significant. Milk with off-flavor also had sig nificantly higher concentrations of hexanal. The data were also analyz ed by principal component regression. The results from this analysis i ndicated that the causative factors for the oxidation were different f or the two herds.