Lipid oxidation of dried silver cyprinid fishmeal as an impediment in the manufacture of aquafeeds

Dietary lipid oxidation is a salient quality issue in aquafeeds that has been neglected. Oxidized lipids get into aquafeeds mainly through poorly processed fishmeal and oils and tend to build up during feed processing and storage. In this study, lipid oxidation levels and proximate composition were investigated in Rastrineobola argentea fishmeal dried by artisanal methods and in a separate experiment where it was salted and indirectly dried on air-ventilated raised racks. Samples were drawn in the dry and wet seasons at 30 day interval for 90 days. Free fatty acids (FFA), peroxide value (POV) and thiobarbituric acid-reactive substances (TBARS) were used to monitor lipid oxidation stability, while proximate composition was based on moisture, ash, crude protein (CP), crude fat (EE) and gross energy (GE). Lipid spoilage was higher in fishmeal dried directly on bare ground and in that on mesh laid on ground compared to the one dried on air ventilated raised racks. There was higher lipid hydrolysis in the wet season than in the dry season. Salting and indirect drying were associated with elevated lipid hydrolysis and oxidation. Crude lipid decreased as moisture increased with storage time, while crude protein and GE were not significantly affected by season, processing methods or storage time. Ash was highest in salted R. argentea and that dried on bare ground. Both lipid degradation and crude protein loss were minimal in R. argentea dried on air-ventilated raised racks. Accordingly, drying R. argentea on raised racks without salting is adequate. Further considerations should be made to treatment of R. argentea with antioxidants to combat lipid oxidation spoilage as soon it is harvested and during processing and storage.