Studies on the Brown Discoloration of Heated Phospholipids. I

Abstract

It is well known that the brown discoloration is observed by the heating of phospholipids. It has long been presumed that this brown discoloration was due to the reaction among amino group and carbonyl compounds which are formed by the heating of phospholipids. However, little knowledge has been obtained on the mechanism of the browning reaction.in order to elucidate the reaction mechanism of browning, model experiments were carried out. Soybean lecithin was heated with water at 180°C in liquid paraffin, and brown products (BP) thus formed, were isolated by gel-permeation chromatography on Sephadex LH-20 and cellulose column chromatography. The IR absorption spectrum and elemental analysis of BP were similar to those of original lecithin. BP was hydrolyzed by phospholipase A and yielded free fatty acids. In another experiment, acidhydrolysis of BP was carried out, thereby choline and phosphoric acid were noticed in water, and brown compounds (BC) moved into chloroform. Trace amounts of nitogen were determined from BC in chloroform. After reduction of BP with sodium borohydride, colorintensity diminis hed.From these results, the authors concluded that BP seems to be a polymer retaining the structure of original lecithin and is similar to the products formed in aldol condensation reaction rather than Maillard reaction.