Effect of dietary soybean meal and its components on the quality of rainbow trout fillets: Isoflavone deposition and lipid oxidative status

The limited supply of fish meal has led to increased research on various alternate proteins for their suitability as a substitute to fish meal, which is the traditional protein source in aquaculture diets. Low cost, consistent availability, and excellent nutritional profile make soy an excellent candidate as an alternate protein. However, the off-flavors said to be associated with some chemical components of soy, such as the isoflavones, may limit its use in aquaculture.; The main objectives of this research were to determine if dietary soybean meal or its components influenced the product quality of rainbow trout fillets and whether isoflavones were transferred from the diet into fish muscle. Another objective was to determine if the reduced lipid oxidation observed in the fillets of soy fed trout could be attributed to a specific soy component. Dietary genistein but not dietary soybean meal resulted in deposition of isoflavone into trout muscle. Neither dietary genistein nor dietary soybean meal had any adverse effects on fillet quality at the levels used in this study. Fillets from both genistein-fed rainbow trout and soybean meal-fed rainbow trout exhibited reduced lipid oxidation during refrigerated storage. Antioxidant studies of methanol and aqueous extracts from diets containing 40 percent soybean meal showed that such diets had higher free radical (DPPH*) scavenging capacity in comparison to similar extracts from soy isolate and soybean meal, but not the highest concentration of total phenols.; The findings of this research may be of interest to soy farmers, aquaculturists, retailers, and consumers, all of whom are concerned with the production or consumption of a cost effective and high quality fillet product.