Study of the effect of water activity on lipid oxidation

Abstract

The effects of water activity on lipid oxidation were studied in freeze-dried emulsion composed of linoleic acid and gelatinized soluble starch. Water activity of freeze-dried emulsion was adjusted by peristaltic pump in closed system at constant temperature. The apparatus showed high efficiency in both cases of water activity determination and adjustment. It was possible to check the degree of oxidation by peroxide value test. Lipid oxidation was checked in the water activities of 0.11 and 0.65. The reaction rate of oxidation was faster in the water activity of 0.65 than that of oxidation in the water activity of 0.11 as shown in peroxide value change vs. incubation time. In order to compare the reaction rate constants, the peroxide values were evaluated kinetically. The kinetic data indicated that in cases of water activities 0.01 and 0.65, reaction rate constants were different in the monomolecular decomposion period of hydroperoxide, but those were equal in the bimolecular decomposition period, of hydroperoxide.