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Irradiation-Induced Changes in Milk Fat^{1, 2,}

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

ABSTRACT

Gamma irradiation of milk fat under reduced atmospheric pressure produced free monocarbonyls at a rate proportional to irradiation dose. The 2-thiobarbituric acid number and total carbonyls increased, but not at a linear rate. Small quantities of hydroperoxides were produced; radiation dosages higher than 1.5 Mrad decreased the concentration. The flavor of the irradiated fat appeared to have three components: hydrolytic rancidity, oxidized, and candle-like.

The monocarbonyls of irradiated fat were isolated and analyzed by gas chromatography and as 2,4-dinitrophenylhydrazine derivatives. Alkanals predominated and their order of decreasing concentration in the irradiated fat was: C₁₆, C₁₅, C₁₄, C₁₂, C₁₀, C₆, C₈, C₇, C₄, iso-C₄, C₉, C₅, C₃, C₂, C₁. Methyl ketones also were produced by irradiation and the following compounds were found: C₁₅, C₁₁, C₉, C₇, C₅, C₄. Indirect evidence is presented indicating that the long-chain aldehydes are responsible for the candle-like defect. It is suggested that the long-chain aldehydes and methyl ketones are produced via hydrolytic rather than oxidative mechanisms.

¹ Technical Paper no. 1696, Oregon Agricultural Experiment Station.

² This investigation was supported by Public Health Service Research Grant No. EF-182 from the Division of Environmental Engineering and Food Protection.

³ Fellow of the Greek State Scholarship Foundation.