Maximization of the docosahexaenoic and eicosapentaenoic acids content in concentrates obtained from a by-product of rainbow trout ( Oncorhynchus mykiss ) processing

This study was focused on a by-product (i.e., belly muscle) resulting from the commercial processing of rainbow trout ( Oncorhynchus mykiss ). In it, n-3 long-chain polyunsaturated fatty acid (LCPUFA) concentrates were obtained from the belly oil by optimization of the urea-complexation process variables. Thus, the effect of urea:fatty acids (FA) ratio (0–6, w/w), crystallization temperature (− 30 to 30 °C), crystallization time (3.0–48.0 h) and stirring speed (0–1000 rpm) on the eicosapentaenoic acid (EPA, C20:5n-3) and docosahexaenoic acid (DHA, C22:6n-3) contents in concentrates was analyzed by response surface methodology. As a result, high values were obtained for total FA yield recovered, and contents on LCPUFA, EPA and DHA in the non-urea complexing fraction, as well as a great retention of saturated and monounsaturated FA in the urea-crystal adducts. After validation of the model obtained, the combination of process variables levels that maximizes the desirability function (0.91 score) for response variables was 4.21, ‒15 °C, 24 h and 1000 rpm, respectively. In agreement with the great significance and availability of farmed rainbow trout, belly muscle by-product confirmed to be a profitable source of n-3 LCPUFA to be commercialized as an added-value component.