Effects of green tea natural extract on quality parameters and lipid oxidation during storage of tench (Tinca tinca) fillets

The study investigated the effects of two levels of green tea extract (GTE) on common quality parameters and lipid oxidation of tench fillets for up to 7 days of refrigerated (+2°C) and 45 days of frozen storage (-25°C). Sixty-eight tench (93.2 ± 25.7 g) were killed by live chilling (water : ice ratio = 1 : 1; T = 2-4°C) and then filleted. Four fillets were set aside (not treated, NT) while the remaining were divided into four groups which were treated with a sprayed-on solution of: distilled water/ethanol 95% v/v mixture (control group, C); ascorbic acid (AA); and two levels of GTE (0.05% w/v GTE5 and 0.1% w/v GTE10, respectively). Tested were fillet quality parameters (pH, colour, fillets texture and water holding capacity), chemical composition, and lipid oxidation products. Moreover, in NT and refrigerated fillets the total viable counts, Enterobacteriaceae, Pseudomonas spp., yeast and moulds microorganisms were assessed. Results showed that GTE at both levels had no negative effects on pH, colour, texture or free water, with results comparable to AA used as a reference synthetic antioxidant. At 7 days of refrigeration, the GTE-treated fillets showed a similar antioxidant capacity of synthetic AA in retarding lipid oxidation. In frozen samples, the best results were obtained by GTE5 treatment while GTE10 seemed to exert a pro-oxidant effect. No significant inhibitory effects of GTE were observed in the microbiological parameters.