Effect of Milk Composition on the Partition Coefficients of Diacetyl, Acetaldehyde, and Ethanol in Acidified Milk Products

¹ Department of Food Science and Nutrition, University of Minnesota, St. Paul 55108, and Department of Animal Science, Texas A&M University College Station 77843

Acidified milk samples were prepared with fat concentrations from 0 to 20% and SNF concentrations from 8 to 12%. The partition coefficients of diacetyl, acetaldehyde, and ethanol were determined in these acidified samples at pH 4.4 and 4.6 and at 30 and 50°C. Gas chromatographic headspace analysis was used to quantitate these flavor compounds after the system reached equilibrium.

The pH did not affect the partition coefficients. Partition coefficients were dependent on the incubation temperature and were higher at 50°C. Concentration of the flavor compounds significantly affected their distribution between the air and aqueous phases. Diacetyl, acetaldehyde, and ethanol partition coefficients increased as SNF and milk fat concentrations increased in the milk matrix at either concentration of compounds or incubation temperature. The partition coefficients were highest in a milk matrix that contained 12% SNF or 20% milk fat. There were no interaction effects of SNF by fat, SNF by pH, fat by pH, or SNF by fat by pH on the partition coefficients; an interaction of fat by pH for diacetyl existed. The partition coefficient for acetaldehyde was higher than the partition coefficient for diacetyl. The partition coefficient was lowest for ethanol.

Key Words: partition coefficient • gas • chromatographic headspace analysis • acidification • milk products

Submitted on October 24, 1994
Accepted on July 27, 1995