Obtention of functional compounds from fish oil and protein

Abstract

Fish discards represent both an underutilization of fishing stock and an environmental problem. Consequently, the European Commission has undertaken a depth reform regarding common fisheries, so-called the zero-discard policy. This new regulation implies that all the catches must be landed resulting in a high amount of fish biomass. Hence, technical solutions able to convert the fish discards into added-value compounds must be developed and optimized. The aim of this PhD research is to develop new processes for the up-grading of oil and protein extracted from fish discards to produce functional compounds of interest for the pharmaceutical and food industry. In the area of lipids, the composition and regiodistribution of six discarded species of the Alboran Sea was seasonally studied. Oils extracted from small-spotted catshark and bogue contained PUFA with high sn-2 regioselectivity and have been proposed as substrate for the production of 2-MAG. In the case of oils extracted from sardine, axillary seabream, blue whiting and horse mackerel polyunsaturated fatty acids (PUFA) were more randomly distributed. Consequently, these oils have been recommended as a substrate for the production of PUFA concentrates by physical methods. Theoretical studies aimed at mechanistically model the production of PUFA concentrates by winterization of free fatty acids at low temperature and by lipase mediated-hydrolysis of fish oil in microaqueous systems were conducted. Winterization was the most efficient process, achieving high increase of PUFA content (1.7-fold). Finally, an up-grading process aimed at producing MLM structured lipids from sardines discards was developed. MLM are functional compounds highly demanded in the pharmaceutical industry. The process was composed of (i) fish oil extraction, (ii) Omega-3 concentration via low temperature winterization, (iii) enzymatic esterification and (iv) triacylglycerols (TAG) extraction via liquid chromatography. The resulting MLM structured lipid met the oxidative conditions required for refined oils Fish protein was employed as a substrate for the production of bioactive peptides (i.e. antihypertensive and antioxidant activities) employing a mixture of bacterial and animal proteases. In this case, a crossed mixture-process model was proposed involving percentage of subtilisin in the enzyme mixture, concentration of protein in the reaction volume and temperature as input variables. Additionally, fish protein hydrolysates (FPH) were evaluated as potential compounds able to physically and oxidatively stabilize fish oil emulsions and microcapsules produced by spray-drying. The process of homogenization and spray-drying did not affect the stability of the oil and presented high yield (98%). After 80 days of storage, the encapsulated oil exhibited a similar course of hydroperoxide content as reported for microencapsulated fish oil prepared from other matrix systems. These microcapsules may enlarge the shelf-life of fish oil and, therefore, find applications in the food industry as delivery systems.

The main objective of this PhD research is to develop new processes for the obtention of functional compounds from fish discards. To that end, this investigation has been focused in the two majority components of fish: lipids and proteins.