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Stability of Lysine, Methionine, and Tryptophan in Dried Whey Concentrate During Storage

Department of Food Science, University of Wisconsin, Madison 53706

ABSTRACT

Samples of dried whey protein concentrate at water activities .15, .24, .31, and .41 were stored for up to 6 mo at –40, 5, 20, and 40°C. After storage the protein was hydrolyzed and the concentrations of methionine, available lysine, and tryptophan were determined by HPLC. Methionine and tryptophan contents did not change significantly during storage at any of the conditions tested. The available lysine content decreased most at the highest water activity (.41) and the highest temperature (40°C), the loss being 23% after 3 mo. Losses of lysine were influenced more by temperature than by water activity within the range of conditions tested. At temperatures of 20°C or lower, losses of lysine after 6 mo of storage were less than 8% at all water activities tested.

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