Anti-discoloration effect of phytochemicals mixture extracted from mango leaf (Mangifera indica), guava leaf (Psidium guajava), and green tea residue (Camellia sinensis var. sinensis cv. Chin-shin Dah-pang) on stored Nile tilapia (Oreochromis niloticus) fillets

Abstract

Discoloration is a critical limitation in the storage of fish meat. In this study, the antioxidant and antimicrobial activities of phytochemicals extracted from mango leaf, guava leaf, and green tea residue and a mixture of these phytochemicals (1:1:1, w/w/w) were initially evaluated in vitro. Compared with the individual byproducts, the mixture exhibited higher antioxidant and antimicrobial activities and was selected for use as a feed or processing additive. The half-maximal inhibitory concentration of the phytochemicals mixture for 2,2-diphenyl-1-picrylhydrazyl scavenging activity was calculated as 10.46 μg/mL. In addition, the minimum inhibitory concentration and minimum bactericidal concentration of the mixture against Aeromonas hydrophila, Edwardsiella tarda, Escherichia coli, Lactococcus garvieae, Pseudomonas aeruginosa, Staphylococcus aureus, and Streptococcus iniae ranged from 0.20 to 12.50 mg/mL. Nile tilapia were fed with diets containing different concentrations of the phytochemicals mixture, namely 0.0% (control), 0.5%, 1.0%, and 2.0%, for a duration of 8 weeks before filleting. The results indicated that the growth performance of the fish was not affected by the phytochemicals mixture. In the immersion treatment, half of the fillets from the control group were immersed in a solution containing a 1 mg/mL phytochemicals mixture and air-dried. During the storage period, chromatic analysis revealed a stable increase in the CIE b* value, with both dietary and immersion treatments significantly inhibiting discoloration (p < 0.05). Overall, both the peroxide value and total plate count results indicated that the anti-discoloration effect of the phytochemicals mixture was primarily ascribed to its antioxidant properties.