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Effect of Temperature of CO₂ Injection on the pH and Freezing Point of Milks and Creams¹

Northeast Dairy Foods Research Center, Department of Food Science, Cornell University, Ithaca, NY 14853

Corresponding author: David M. Barbano; e-mail:
dmb37{at}cornell.edu.

The objectives of this study were to measure the impact of CO₂ injection temperature (0°C and 40°C) on the pH and freezing point (FP) of (a) milks with different fat contents (i.e., 0, 15, 30%) and (b) creams with 15% fat but different fat characteristics. Skim milk and unhomogenized creams containing 15 and 30% fat were prepared from the same batch of whole milk and were carbonated at 0 and 40°C in a continuous flow CO₂ injection unit (230 ml/min). At 0°C, milk fat was mostly solid; at 40°C, milk fat was liquid. At the same total CO₂ concentration with CO₂ injection at 0°C, milk with a higher fat content had a lower pH and FP, while with CO₂ injection at 40°C, milks with 0%, 15%, and 30% fat had the same pH. This indicated that less CO₂ was dissolved in the fat portion of the milk when the CO₂ was injected at 0°C than when it was injected at 40°C. Three creams, 15% unhomogenized cream, 15% butter oil emulsion in skim milk, and 15% vegetable oil emulsion in skim milk were also carbonated and analyzed as described above. Vegetable oil was liquid at both 0 and 40°C. At a CO₂ injection temperature of 0°C, the 15% vegetable oil emulsion had a slightly higher pH than the 15% butter oil emulsion and the 15% unhomogenized cream, indicating that the liquid vegetable oil dissolved more CO₂ than the mostly solid milk fat and butter oil. No difference in the pH or FP of the 15% unhomogenized cream and 15% butter oil emulsion was observed when CO₂ was injected at 0°C, suggesting that homogenization or physical dispersion of milk fat globules did not influence the amount of CO₂ dissolved in milk fat at a CO₂ injection temperature of 0°C. At a CO₂ injection temperature of 40°C and at the same total CO₂ concentration, the 15% unhomogenized cream, 15% vegetable oil emulsion, and 15% butter oil emulsion had similar pH. At the same total concentration of CO₂ in cream, injection of CO₂ at low temperature (i.e., <4°C) may produce a better antimicrobial effect during refrigerated shelf life due to the higher concentration of CO₂ in the skim portion of the cream.

Key Words: carbon dioxide • pH • freezing point • milk and cream

Abbreviation key: FP = freezing point

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