Studies on the Brown Discoloration of Heated Phospholipids. II

Abstract

In a previous paper the authors reported that browning products (BP) which were formed in heated lecithin seemed to be compounds retaining the structure of original lecithin, but polymerized at the fatty acid parts.The above mentioned properties of BP suggest that fatty acid constituents of original lecithin are modified in the early stage of browning reaction. The present paper deals with isolation of a major intermediate product (IP) from BP. IP was isolated from heated lecithin by silicic acid column chromatography, thus obtained IP was heated and the color of this products was compared with heated lecithin. The results indicated that brown color developed more in heated IP than in heated lecithin. After reduction of carbonyl groups in IP with sodium borohydride, the products did not produce the brown color. These results led the authors to conclude that carbonyl groups participated in browning reaction. From the results of investigation of carbonyl compounds authors found that the main carbonyl compounds were 9-oxo-10, 12-octadecadienoic acid and 13-oxo-9, 11-octadecadienoic acid which were conjugated dienone compounds.From these results, the authors presumed that conjugated dienone compounds were formed in the early stage of browning reaction by heating of lecithin, and these carbonyl compounds were polymerized by catalytic action of choline and/or phosphoric acid which were constituents of lecithin.