Vitamin Stability and Growth of Psychrotrophic Bacteria in Refrigerated Raw Milk Acidified with Carbon Dioxide

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Abstract
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, 13-cis-retinol, β-carotene, α tocopherol, γ tocopherol, thiamin and riboflavin—and on the growth of psychrotrophic spoilage bacteria 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 samples as well as the controls were stored at 7°C for 7 days and analyzed daily for the fat-soluble vitamins and growth of psychrotrophic bacteria. Thiamin and riboflavin were analyzed only at the beginning and the end of the period studied (days 0 and 7). No significant variations (P ≤ 0.05) of the content of all-trans-retinol, beta-carotene, α and γ 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 variations were observed in the treated samples as well as in the controls, so it can be assumed that the treatments studied for preservation of milk did not cause changes in vitamin retention during cold storage. Psychrotrophic counts were inhibited significantly (P ≤ 0.05) by the presence of CO2 after 2 to 3 days of storage, and no significant differences (P ≤ 0.05) were found between samples acidified to pH 6.0 and 6.4.

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