Influence of Carbon Dioxide Addition to Raw Milk on Microbial Levels and Some Fat-Soluble Vitamin Contents of Raw and Pasteurized Milk

The effect of the application of CO 2 to extend the cold storage of raw and pasteurized milk on the content of fat-soluble vitamins of milk was investigated. CO 2 -treated milk (pH 6.2) was compared with a control (unacidified) milk. CO 2 -treated and control raw milk samples were stored at 4 °C for 4 days. CO 2 -treated milk was then vacuum degasified, and both control and treated samples were pasteurized and stored at 4 °C for 7 days. CO 2 addition inhibited the growth of microorganisms in raw milk without affecting the stability of vitamin A (retinol and β-carotene) and vitamin E (α-tocopherol). Acidity and pH data indicated that subsequent vacuum degasification and pasteurization on a pilot scale partially removed CO 2, making milk acceptable for liquid consumption. However, the residual CO 2 present extended the cold-storage period of pasteurized milk by inhibiting bacterial survivors without detrimental effects on retinol, β-carotene, and α-tocopherol. Slightly higher (not statistically significant, p > 0.05) concentrations of retinol, β-carotene, and α-tocopherol were detected during cold storage in raw and pasteurized CO 2 -treated milk with respect to the control milk, which could be related to a certain protective effect of the CO 2 . Keywords: Milk; carbon dioxide; psychrotrophs; cold storage; fat-soluble vitamin