Effect of amino acids on the autoxidation of safflower oil in emulsions

Oxygen absorption rates were measured on liquid emulsions containing safflower oil and various amino acids. The antioxidant effects of the several amino acids were quite variable depending on the type of emulsifier used, the pH of the system and the presence of added sugar. Preliminary tests with Maillard reaction products obtained by heating dextrose with lysine showed little stabilizing effect. In freeze-dried emulsions, methionine, threonine, lysine and histidine all exhibited antioxidant activity. With sodium caseinate as the matrix, methionine was much better than any of the other amino acids. The inclusion of sugar enhanced the rate of oxidation. Porosity measurements on the freeze-dried powders revealed that oxygen diffusion was not rate-determining. When xanthan gum was used to replace caseinate in these dried emulsions, oxidation rates increased.