Effect of storage of rainbow trout (Oncorhynchus mykiss) by-products on fatty acids composition, oxidation, and nutritional properties of hydrolyzed-derived oils

The effects of storage of rainbow trout processing by-products at 4 ºC on fatty acid composition and nutritional values of hydrolyzed-derived oils were determined. Polyunsaturated fatty acids (PUFA, 39.97-43.70%) were the major fatty acids followed by monounsaturated (MUFA, 31.90-34.05%) and saturated (SFA, 19.27-22.59%) fatty acids. Among fatty acids, linoleic, cis vaccinic, and palmitic were the main fatty acids. N-6 fatty acids represented 34-38% while n-3 fatty acids were 4.5-6.6% of all fatty acids (P<0.05). Hypocholesterolemic/hypercholesterolemic ratio (h/H) index in oils was between 4.23 and 5.15. The highest value was found at day 2 while showed no changes among other storage times (P>0.05). Thrombogenic index (TI) at days 0 and 2 were the lowest among storage times while at days 5 it represented the highest value. However, the change was not significant (P>0.05). N-6/n-3 ratio ranged from 5.01 to 7.6. PUFA/SFA was between 1.77 and 2.29 and showed the highest value at day 2 while after 5 days significantly decreased (P<0.05). The highest fish lipid quality (FLQ) index was for fresh by-products (day 0) (P<0.05) and showed no differences from day 1 to 5 (P>0.05). Also, nutritive value index (NVI) ranged from 2.25 to 2.55 with no significant differences during storage (P>0.05). The sum of EPA and DHA was between 1.73 and 4.05% and decreased with increasing storage days (P<0.05). Polyene index (PI) decreased to the end of storage time up to 4 days compared with the fresh by-products and significantly decreased thereafter after 5 days (P<0.05). Results of the present study showed that fatty acid composition and nutritional quality of oils from hydrolysis-derived oils were influenced by the storage days to some degree.