IDENTIFICATION AND BIOCHEMICAL EVALUATION OF THE EFFECTS OF NONENZYMATIC BROWNING REACTION IN THE DIET OF RAINBOW TROUT (SALMO GAIRDNERI)
The increased utilization of less expensive, more abundant alternative sources of protein as a substitute for high quality fish meal in cultured fish feeds may be predicted as the demand for fish for human consumption increases. The use of these sources of protein often necessitates special processing conditions (i.e. increased heat and pressure) and longer storage periods of the feed or feedstuffs, which can lead to undesirable chemical reactions and reduced protein quality and amino acid availability to the animal. Nonenzymatic browning reactions, which include the Maillard reaction and those involving decomposition products of lipid oxidation, are common and typical reactions of this sort. The present study examined the consequences of nonenzymatic browning reaction in the diet of rainbow trout (Salmo gairdneri), and evaluated methods of estimating amino acid availability and utilization with this animal. A model browning reaction (early Maillard-type) system was employed for this purpose. Growth and feed utilization were significantly depressed by the presence of browned protein in the diet of rainbow trout. Amino acid analysis following acid hydrolysis of browned protein samples underestimated the loss of biologically available lysine, as did TNBS-reactive lysine, based on the growth and plasma free lysine response to feeding. Although arginine and lysine were the amino acids most affected by the reaction under the conditions employed, only the loss in lysine was of nutritional significance in the diets as formulated. Digestibility of protein and apparent absorption of amino acids in vivo by rainbow trout was found decreased in the groups fed the browned protein diets. An in vitro enzymatic hydrolysis procedure using pronase indicated most of the loss in lysine to be due to formation of (epsilon)-deoxy-fructosyl-lysine from lysine residues. This compound was detected in the plasma of fish fed the browned protein diets, and apparently absorbed intact, but not further metabolized. A biochemical method was employed to estimate lysine availability to rainbow trout, based on the plasma free lysine response to feeding basal diets containing control or browned proteins with graded levels of supplemental lysine. The results indicated the in vitro enzymatic hydrolysis procedure to be more sensitive than other standard methods routinely used for estimating biological availability of amino acids. Plasma free amino acid analysis was demonstrated to be a valuable tool for determining limiting amino acid(s) in the diet, and estimating amino acid availability and utilization by rainbow trout.
STEVEN MICHAEL PLAKAS,
"IDENTIFICATION AND BIOCHEMICAL EVALUATION OF THE EFFECTS OF NONENZYMATIC BROWNING REACTION IN THE DIET OF RAINBOW TROUT (SALMO GAIRDNERI)"
Dissertations and Master's Theses (Campus Access).