VITAMIN STABILITY AND GROWTH OF PSYCHROTROPHIC BACTERIA IN REFRIGERATED RAW-MILK ACIDIFIED WITH CARBON-DIOXIDE

The effect of the application of CO2 for extending the storage life of raw cow's milk on the retention of some vitamins-all-trans-retinol, 1 3-cis-retinol, beta-carotene, alpha tocopherol, gamma tocopherol, thia min and riboflavin-and on the growth of psychrotrophic spoilage bacter ia has been studied. Raw cow's milk samples were acidified by bubbling CO2 through them to pH 6.0 and 6.4. Two different controls were used: untreated milk (pH 6.83) and degasified milk (pH 6.85). The treated s amples as well as the controls were stored at 7 degrees C for 7 days a nd analyzed daily for the fat-soluble vitamins and growth of psychrotr ophic bacteria. Thiamin and riboflavin were analyzed only at the begin ning and the end of the period studied (days 0 and 7). No significant variations (P less than or equal to 0.05) of the content of all-trans- retinol, beta-carotene, alpha and gamma tocopherol and riboflavin were observed in all samples studied. In contrast, during the first 4 days 13-cis-retinol doubled from the initial content. A slight decrease of thiamin was observed at the end of the storage period. These variatio ns were observed in the treated samples as well as in the controls, so it can be assumed that the treatments studied for preservation of mil k did not cause changes in vitamin retention during cold storage. Psyc hrotrophic counts were inhibited significantly (P less than or equal t o 0.05) by the presence of CO2 after 2 to 3 days of storage, and no si gnificant differences (P less than or equal to 0.05) were found betwee n samples acidified to pH 6.0 and 6.4.