Antioxidant Potential of Guava Leaf Extracts and Its Preservative Effects on the Shelf Life of the Grass Carp (Ctenopharyngodon idella) Fillets Under Refrigerated Condition

The antioxidant activity of guava leaf extracts (GLE) was evaluated for their efficacy in enhancing the quality and extending the shelf life of grass carp (Ctenopharyngodon idella) fillets stored at a refrigerated temperature of 4 ± 1 °C for 16 days. The phytochemical content and antioxidant capacities of GLE were first determined, followed by periodic assessments of chemical, bacteriological, and sensory attributes in control and ethanolic GLE-treated fillets at concentrations of 1, 2, 3, and 4%. The results revealed that the absolute ethanol extracts of guava leaves contained the highest total phenolic content (170.32 mg GAE/g extract), total flavonoid content (51.98 mg QE/g extract), and antioxidant activity, significantly higher (P< 0.05) than 50% ethanol and water extracts. During the storage period, fish fillets treated with 3 and 4% GLE showed notably lower levels of pH, free fatty acids (FFA), thiobarbituric acid reactive substances (TBARS), and total volatile basic nitrogen (TVB-N) compared to the control and other treated groups. The highest aerobic plate count (APC) was reached on day 8 in the control group (7.24 log CFU/g), followed by the 1% (7.02 log CFU/g) and 2% GLE treatments (7.18 log CFU/g). In contrast, the 3 and 4% GLE treatments delayed microbial growth, reaching their highest APC values on day 16 (6.97 and 6.77 log CFU/g, respectively). Sensory evaluation showed that the 3 and 4% GLE-treated fillets maintained acceptable quality until day 12 of storage, whereas the control fillets were deemed unacceptable after just 4 days. Since no significant difference was found between the 3 and 4% treatments, the study suggests that 3% GLE is an effective, plant-based preservative for maintaining the quality and extending the shelf life of grass carp fillets during refrigeration.