Effect of frozen storage on fatty acid composition and changes in lipid content ofScomberomorus commersoniandCarcharhinus dussumieri

Abstract

Department of Food Technology, College ofAgriculture, Tarbiat Modares University, Tehran, IranSummaryInvestigated were the changes in fatty acid composition,oxidation and enzymatic deterioration of lipids in frozen()30 C) fish fillets from the Persian Gulf. The narrow barredSpanish mackerel (Scomberomorus commersoni) and whitecheek shark (Carcharhinus dussumieri) were tested with storagetimes of 0, 1, 2, 3, 4, 5 and 6 months at )18 C. Statisticalresults showed that the major fatty acids among the saturatedand monounsaturated fatty acids of each fish species werepalmitic (C16:0) and oleic (C18:1n-9) acids, respectively. Bothlinoleic acid (C18:2n-6) and arachidonic acid (AA) (C20:4n-6)were predominant in total n-6 polyunsaturated fatty acids inboth mackerel and shark. The EPA (eicosapentaenoic acid;C20:5 n-3) and DHA (docosahexaenoic acid; C22:6 n-3) acidswere the major fatty acids among total n-3 acids in both fishes.During frozen storage, the PUFA (40.1 and 23.94%), n-3 (48and 42.83%), x3 ⁄ x6 (41.36 and 50%), PUFA ⁄ SFA (56 and42.23%) and EPA + DHA ⁄ C16 (55.55 and 46.66%) con-tents decreased in S. commersoni and C. dussumieri, respec-tively. Also peroxide, thiobarbituric acid (TBA) and free fattyacid (FFA) values significantly increased (P < 0.01) with thetime of storage.IntroductionMarine lipids have a high content of polyunsaturated fattyacids (PUFAs), particularly eicosapentaenoic (EPA; 20:5x-3)and docosahexaenoic acids (DHA; 22:6x-3) (Pazos et al.,2005; Bayir et al., 2006). There is strong evidence thatconsumption of fish is favourable to human health (Bayiret al., 2006). It is generally recognized that PUFA compositionmay vary among fish species.Degradation of PUFA by auto-oxidation during storageand the processing of fish oils and fatty fish easily leads toformation of volatiles associated with rancidity (Pazos et al.,2005). For this reason, freezing and frozen storage have largelybeen employed to retain fish sensory and nutritional properties(Lugasi et al., 2007). Although frozen storage of fish caninhibit microbial spoilage, the muscle proteins undergo anumber of changes (causing insolubility and formation ofaggregates) which modify their structural and functionalproperties. However, it is widely acknowledged that lipidoxidation may also be involved (Badii and Howell, 2002).Moreover, fish undergo quality changes during chilling andfrozen storage. The high degree of unsaturated lipids makesfish tissues highly susceptible to peroxidation and rapiddeterioration. Oxidative changes are mainly related to tasteand texture of the fish. In later stages of lipid peroxidation,changes in colour and nutritional value are observed (Dragoevet al., 1998).Our study was aimed at determining the fatty acid (FAs)composition and oxidative changes in fish fillets (narrow-barred Spanish mackerel and white cheek shark being the mostimportant fishes in the Persian Gulf: Fishery Statistics, 2005)caused by lipid peroxidation during frozen storage as animportant factor in quality control of frozen fishery products.Materials and methods