Monola versus Canola as fish oil replacer in rainbow trout : effects on final product quality

Due to economical and environmental concerns, the substitution of dietary fish oil is increasingly implemented by global aquafeed manufacturers. In consideration of its ready availability, large global supply, relatively stable price and overall nutritional characteristics, canola (rapeseed) oil is currently one of the preferred vegetable oils used for fish oil substitution. Recently, monounsaturated fatty acids (MUFA), of which canola oil is rich, have been shown to spare long chain omega-3 polyunsaturated fatty acids (n-3 LC-PUFA) from beta-oxidation for energy production. Thus, the potential of selected canola cultivars richer in MUFA, such as Monola, as a partial fish oil replacer in aquafeed formulations are currently of significant interest. In this study, a direct comparison of Canola oil (CO) and Monola oil (MO) was assessed by a 3×2 factorial in vivo feeding trial, in which the two oils were used to substitute fish oil at three different levels (60, 75 and 90%), with treatments subsequently named CO60, CO75, CO90, MO60, MO75 and MO90, respectively. The two tested oils were both in crude form, and the diets were formulated and manufactured to be iso-proteic (40%) and iso-lipidic (20%), varying only in the source of the added dietary lipid. Triplicate groups of juvenile rainbow trout (Oncorhynchusmykiss) (~5g) were fed one of the six treatments over the entire production cycle until fish reached a commercial size (~400 g) 27 weeks later. In order to study the effects of the different dietary lipid sources on the quality of final product, sensory and chemical analyses were performed on fish fillets at the end of the feeding trial. Cooked fillets were assessed for their organoleptic/sensorial attributes using a panel test and their volatile profiles were determined using SPME-GC-MS analysis. Instrumental color analysis was carried out with a Minolta chromameter, together with the total carotenoid determination. Tissue proximate and fatty acid composition of fillets were performed according to AOAC methods. Multivariate analyses, such as L-PLS regression analysis, were then applied to sensory and analytical data and the results will be presented and discussed, towards a better understanding of how different dietary lipid sources can modify the final quality of aquaculture products.