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Development and Flavor Properties of Methyl Ketones in Milk Fat^1,2,

Department of Food Science and Technology, Oregon State University, Corvallis

ABSTRACT

Temperature during heat treatment, time of heat treatment, and presence of water in milk fat all influenced the quantity of methyl ketones produced. Maximum yield of ketones was obtained by heating a degassed fat sample for 3 hr at 140 C; heating an additional 15 hr had no further effect. Milk fat prepared by degassing at 2 to 5 µ Hg for 1 hr at 40 C still contained sufficient water for maximum ketone production. When milk fat was dried over calcium hydride for 18 hr prior to heat treatment, methyl ketone formation was inhibited. Hence, water appears essential for significant heat-induced ketone formation in milk fat. Heating the fat in the presence of air caused a slight increase in yield of ketones.

The average flavor threshold (AFT) for each of the methyl ketones, produced by heating milk fat, was determined in homogenized milk. Based upon the AFT of individual ketones and the AFT of the ketone mixture, prepared in the ratios found in the fat, the following conclusions are warranted: 1. The ketone mixture exhibits a synergistic interaction whereby a perceptible flavor is evident when the concentrations of all components in the mixture are below their AFT; 2. There is sufficient methyl ketone precursor in milk fat to give rise to perceptible flavors in a beverage-type milk.

¹ This investigation was supported by PHS Grant EF-00532-01.

² Technical Paper No. 1840, Oregon Agricultural Experiment Station.