Nonenzymic browning. VI. Browning produced by oxidized polyunsaturated lipids on storage with protein in presence of water

Oxidized methyl esters of polyunsaturated fish oil fatty acids were stored with casein soaked in water at 4 and at 60° C. The more oxidized sample was less completely extracted from the reaction mixture because it was bound in higher degree in insoluble products of browning reactions. Changes taking place at 4° and 60° C differed more in the reaction rate than in the reaction mechanisms. The soluble and the insoluble pigments were formed approximately at relatively equal rates. Prolonged storage increased the intensity of browning and also produced a bathochrome shift connected with increased dominant wavelength and saturation, this behaviour being evidently due to the prolongation of conjugated double bond system by further reaction of primary browning products.