METHIONINE STABILITY IN METHIONINE‐FORTIFIED MODEL FOOD SYSTEMS AS INFLUENCED BY METHOD OF METHIONINE INCORPORATION AND BY LIPID OXIDATION

ABSTRACT Model systems were used to evaluate the influences of method of methionine incorporation and lipid oxidation on the stability of added methionine during heating or storage. High pressure liquid chromatography was used to separate and quantify the dansyl derivatives of methionine, methionine sulfoxide and methionine sulfone. In a system undergoing nonenzymatic browning, the loss of added methionine was greater when the methionine was added in water solution than when it was incorporated by dry blending. In systems undergoing lipid oxidation, the initial peroxide value was directly related to the loss of free methionine and the formation of methionine sulfoxide. The conversion of methionine to methionine sulfoxide due to oxidizing lipid was reduced by the presence of protein.