THE PHYSIOLOGICAL EFFECTS OF THE MAILLARD REACTION PRODUCTS ON FISH

The effect of the Maillard reaction on the nutritional quality of protein was studied in Tilapia aurea. Feeding experiments in T. aurea indicated that the conversion efficiencies of 10-days and 40-days browned protein diets were approximately 38% and 28% respectively, when compared with the control, a diet of 0-day browned protein. Destruction of the essential amino acids, especially lysine and arginine, were suggested to be the major causes of this result. To study solely the effect of the Maillard browned products other than Maillard browned protein, a browned tryptophan-glucose mixture (BTG) was added to a 40% casein diet. The results indicated that the incorporation of BTG in the diet suppressed the growth of the fish. The in vivo effect of BTG on the intestinal glycosidases of T. aurea was also studied. Intestinal beta-galactosidase activity of the fish was significantly decreased after ingesting a 4% diet for 6 weeks. The activities of various digestive enzymes (including leucine aminopeptidase, alkaline phosphatase, alpha- and beta-glucosidases, alpha- and beta-fucosidases, beta-galactosidase, beta-galacturonidase, alpha-mannosidase, beta-xylosidase) from tissues of the digestive system and from intestinal fluid of T. aurea were determined. The possible function of each enzyme was discussed. The in vitro inhibitory effects of Maillard browned tryptophan-glucose mixture (BTG) including its water soluble fraction (WSF) and water insoluble fraction (WIF) on the digestive enzymes of T. aurea were evaluated. The inhibitory effects of BTG on the digestive enzymes of T. aurea explain, in part, the poor growth performance of the fish fed diets containing BTG. Also investigated were the in vitro inhibitory effects of the Maillard reaction products (MRP\u27s) derived from various browning model systems, including lysine-glucose, glutamic acid-glucose, glycine-glucose, and methionine glucose mixtures, on the activity of alpha-glucosidase of T. aurea. Results showed that all these Maillard browned amino acid-glucose mixtures inhibited the enzyme, suggesting that the enzymatic inhibitory effect of MRP\u27s from many sources is a common phenomenon. In order to provide information on how browned egg albumin metabolized in the digestive tract of T. aurea, hydrolysis of the Maillard browned egg albumin by the intestinal protease of T. aurea was determined. . . . (Author\u27s abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UM