Effect of Storage of Raw and Pasteurized Goats' Milk on Flavor Acceptability, Psychrotrophic Bacterial Count, and Content of Organic Acids

Abstract

Pasteurization of raw goats' milk either at 63°C for 30 min or 72°C for 15 s within 1 d of milking ensures a better tasting product both initially and during storage at 4.5°C for 6 weeks than if the raw milk is aged for several days at 4.5°C before being pasteurized. Pasteurized milks processed from high-count raw milks aged 1 to 2 weeks had lower acceptability ratings (on a 9-point hedonic scale), which decreased further in cold storage and were independent of bacterial increases in the log phase of growth. Pasteurized milks processed from raw milk 7 or more days old were subject to rapid increases in bacterial numbers in storage if they were trace-contaminated during pasteurization even though initial counts were <100 psychrotrophs/ml. For all raw and pasteurized milks, three peaks were consistently observed from an HPLC analysis designed to monitor some organic acids. Two of the components decreased and the third appeared and increased during storage. Disappearance of one component coincided with appearance of another. These compounds may be associated with loss of flavor quality of the milk since in some instances these changes significantly correlated with the decrease in hedonic ratings of the stored milks.