Fingerlings and marketable size rainbow trout (Oncorhynchus mykiss): Proximate composition, cholesterol content and fatty acid profile in fillets

Abstract

Rainbow trout (Onchorhynchys mykiss) is well known fish species in the nature. Changes in proximate composition of fish meat are associated with age and size of fish. Cholesterol content in animal tissues is associated with feeding method and quality of food, in spite of regulatory mechanism of cholesterol synthesis and absorption. Objective of this study was determination and comparison of proximate composition, cholesterol content and fatty acid profile of fingerlings and marketable size rainbow trout from aquaculture. Samples of fingerlings (average mass of 99 g and length of 18.6 cm) and marketable size rainbow trout (average mass of 229 g and length of 23.3 cm) were collected in August 2010, in the fishpond 'Ribnik', Mrkonjić city, Republic Srpska - Bosnia and Herzegovina. Fingerlings and marketable size rainbow trout were fed complete mixture of similar composition for both fish categories (fish products, oils and fats, cereal products and oil seeds). Obtained results showed that there was no statistically significant difference (p> 0.05) in the content of total lipids (3.81%, fingerlings and 4.17%, marketable size trout) and ash (1.27%, fingerlings and 1.29%, marketable size trout). Higher protein content was determined in marketable size trout fillets (18.69%), as well as lower water content (75.40%) compared to their content in fingerlings (17.72% proteins and 77.11% water). Cholesterol content was 82.59 mg/100g (fingerlings) and 70.12 mg/100g (marketable size trout). Statistically significant differences (p lt 0.05) in content of total saturated fatty acids was established between fingerlings and marketable size trout (31.81% and 29.14%, respectively), also in polyunsaturated fatty acids-PUFA (33.93% and 36.78%, respectively) and n-3 fatty acids (17.17% and 19.20%, respectively). Content of monounsaturated fatty acids was similar and ranged from 33.30%, in fingerlings, to 33.05% in marketable size trout. There was no statistically significant difference (p > 0.05) in content of total n-6 fatty acids in fingerlings (16.76%) and marketable size fish (17.58%). Higher quantities of n-3 PUFA in fingerlings (17.17%) and commercial trout (19.20%) and lower quantities of n-6 PUFA (16.76% in fingerlings and 17.58% in marketable size trout) resulted in favourable n-3/n-6 ratio (1.02 in fingerlings and 1.09 in commercial trout). Content of eicosapentaenoic acid (EPA, C20:5 n-3) and docosahexaenoic acid (DHA, C22:6 n-3) was 2.78% and 8.21% in fingerlings and 3.36% and 9.29% in marketable size fish, respectively. Content of EPA+DHA in total fatty acids was 10.99% in fingerlings and 12.65% in marketable size rainbow trout. By consumption 200 g of this fish intake of desirable fatty acids, EPA and DHA, is 0.84 g in fingerlings, and 1.06 g in marketable size rainbow trout, which is in accordance with recommendation of the American Heart Association for persons with cardiovascular disease (daily intake: in total 1g EPA and DHA). Trout growth was accompanied by increase of the protein content, decrease of the water content and increase in content of PUFA especially n-3 essential fatty acids. Due to significant content of proteins and unsaturated fatty acids and lower amounts of fat, rainbow trout can be considered as one of the most valuable food stuffs in human nutrition.

Kalifornijska pastrmka (Oncorhynchus mykiss) je jedna od najpoznatijih vrsta ribe u prirodi. Promene u hemijskom sastavu mesa ribe su povezane sa starošću i veličinom ribe. Sadržaj holesterola u tkivima životinja je u vezi sa načinom i kvalitetom ishrane, uprkos regulatornom mehanizmu sinteze i apsorpcije holesterola. Cilj ovih ispitivanja je bio određivanje i poređenje hemijskog sastava, sadržaja holesterola i masnokiselinskog profi la mlađi i konzumne kalifornijske pastrmke iz akvakulture. Uzorci mlađi (prosečne mase 99 g i dužine 18,6 cm) i konzumne kalifornijske pastrmke (prosečne mase 229 g i dužine 23,3 cm) su sakupljeni u avgustu 2010. godine u ribnjaku 'Ribnik', Mrkonjić Grad, Republika Srpska - Bosna i Hercegovina. Mlađ i konzumna pastrmka su hranjene kompletnom hranom za pastrmku, sličnog sastava (riblji proizvodi, ulja i masnoće, proizvodi od žita i semena uljarica). Rezultati ispitivanja su pokazali da nema statistički značajne razlike (p > 0,05) u sadržaju ukupnih lipida (3,81%, mlađ i 4,17%, konzumna pastrmka) i pepela (1,27%, mlađ i 1,29%, konzumna pastrmka). U filetima konzumne pastrmke je utvrđen veći sadržaj proteina (18,69%) i manji sadržaj vode (75,40%) u poređenju sa njihovim sadržajem u filetima mlađi (17,72% proteina i 77,11% vode). Sadržaj holesterola je bio 82,59 mg/100 g (mlađ) i 70,12 mg/100 g (konzumna pastrmka). U filetima mlađi i konzumne pastrmke utvrđena je statistički značajna razlika (p lt 0,05) u sadržaju ukupnih zasićenih masnih kiselina (31,81% i 29,14%, respektivno), polinezasićenih masnih kiselina - PNMK (33,93% i 36,78%, respektivno) i n-3 masnih kiselina (17,17% i 19,20%, respektivno). Sadržaj mononezasićenih masnih kiselina je bio sličan i iznosio je u mlađi 33,30% i u konzumnoj pastrmci 33,05%. Nije postojala statistički značajna razlika (p > 0,05) u sadržaju ukupnih n-6 masnih kiselina u mlađi (16,76%) i konzumnoj ribi (17,58%). Veće količine n-3 PNMK u fi letima mlađi (17,17%) i konzumne pastrmke (19,20%) i manje količine n-6 PNMK (16,76% u mlađi i 17,58% u konzumnoj pastrmci) daju povoljan odnos n-3 i n-6 (1,02 u mlađi i 1,09 u konzumnoj pastrmci). Sadržaj eikozapentaenske (EPA, C20:5 n-3) i dokozaheksaenske kiseline (DHA, C22:6 n-3) bio je 2,78% i 8,21% u mlađi i 3,36% i 9,29% u konzumnoj ribi, respektivno. Sadržaj EPA+DHA u ukupnim masnim kiselinama je bio 10,99% u mlađi i 12,65% u konzumnoj kalifornijskoj pastrmci. Konzumiranjem 200 g ove ribe unos poželjnih masnih kiselina, EPA i DHA, iznosi 0,84 g za mlađ, odnosno 1,06 g za konzumnu kalifornijsku pastrmku, što je u skladu sa preporukom Američkog udruženja za srce za osobe sa kardiovaskularnim oboljenjima (dnevni unos: ukupno 1 g EPA i DHA). Rast pastrmke je bio praćen povećanjem sadržaja proteina, smanjenjem sadržaja vode i povećanjem PNMK, naročito n-3 esencijalnih masnih kiselina. Zbog značajnog sadržaja proteina i nezasićenih masnih kiselina i male količine masti, kalifornijska pastrmka se može svrstati u jednu od nutritivno najvrednijih namirnica u ishrani ljudi.