Effect of glucose glycine melanoidins on digestive variables of the rainbow trout fed a non-heated diet

PATRICIO DANTAGNAN; RUIZ, JOCELINE; MORALES, GABRIEL A.; ORELLANA, PAOLA; MÁRQUEZ, LORENZO; HERNÁNDEZ, ADRIÁN J.; SERRANO, XAVIER

San Antonio, Texas, USA

Congreso; Aquaculture AMERICA 2017; 2017

It is known that the thermal processing of nutrient mixtures can affect the digestibility coefficients of diets, together with the change of the nutritional composition of the feed. One of the most ubiquitous changes promoted by the application of heat to a mixture of nutrients is the non-enzymatic browning resulting from the so-called Maillard reaction. The ingestion of strongly browned diets has been proven to decrease the phosphorous digestibility in humans (Delgado-Andrade et al. 2011). In addition, some types of in vitro-synthesized melanoidins exert inhibitory effects on the activity of trypsin from mammals (Hirano et al. 1994, Ibarz et al. 2009). Based on these data, the present work is intended to test if melanoidins can affect the digestive process of cultured fish in a similar way. Glucose-glycine melanoidins (glucose 1M, glycine 1M, NaHCO3 0.1 M, 103°C for 24 hours) were included (1.2%) or not in dietary matrix prepared without heating. The two diets were isoenergetic and isonitrogenous: CP 50.3-50.6%, CL 19.3-19.4%, energy density 23.5-23.6 MJ/kg. The values of gut pH, trypsin-like (substrate BAEE) and chymotrypsin-like (substrate BTEE) activities were post-prandially monitored. Each diet were supplied to three tanks containing 25 rainbow trout juveniles with an average weight of approx. 24 g. Afterwards, each tank were sequentially sampled at 2, 4, 7, 10, 24, 32 and 48 hours post-feeding. Three fish were sampled per tank and temporal point (126 fish). Gastric and duodenal pH´s were measured in situ for each individual. The trypsin-like and chymotrypsin-like activities were measured at pH 8.0 for intestinal crude extracts prepared from one randomly selected fish per tank and temporal point (42 fish). As a result, no effects on gastric pH, duodenal pH and trypsin-like activity were detected, but a decreased chymotrypsin-like activity throughout the digestion process (p < 0.05) was found in the fish fed the browned diet. At least two non-exclusive causes can explain this change in chymotryptic activity: i) a difference in the secretion rate of the enzyme; ii) an interaction between melanoidins and the enzyme in the gut and/or during the preparation of intestinal crude extracts. In any case, the present results suggest a possible role of dietary browning processes on the digestibility of proteins in the rainbow trout mediated by dietary melanoidins, although further research is necessary to ascertain this point.