Effects of alginate coating enriched with tannins on shelf life of cultured rainbow trout (Oncorhynchus mykiss) fillets

This study assesses the potential of two tannins, tannic acid (TAN) and quebracho tannin (QUE), to preserve objective quality parameters of rainbow trout fillets throughout a 15-d cold storage period, applied either alone or combined with alginate coating. Untreated fillets (C), and a set of fillets treated with ascorbic acid (ASC) were also included. All the additives reduced microbial counts and lipid oxidation of fillets, being the effects of TAN and QUE at least comparable to those of ASC, the most widely used antioxidant for fresh fish. The results also indicate that alginate by itself reduced lipid oxidation at late stages of the storage period, and increased fillet lightness (L*) as well, but caused scarce effects on other parameters involved in fillet deterioration. However, alginate and additives applied together enhanced the effects of the additives alone, especially regarding microbial and lipid oxidative parameters, this enabling prolonged shelf life of fillets. These valuable properties of commercial tannins, together with their natural origin and large-scale availability, might well enable further applicability of these substances to fish fillets preservation, not least with regard to coloured species, such as rainbow trout.