Synergistic antioxidant and antibacterial activities of polyphenol extracts from mangosteen peels in preservation of Pangasius hypophthalmus fish balls

In recent years, natural preservatives have attracted more and more attention in food processing since they can enhance food shelf-life and safety. In this study, the polyphenol extract was obtained from mangosteen peels using enzyme-microwave assisted method, characterized for its antioxidant and antimicrobial activities and subsequently used as a natural additive in fish ball preservation. Results revealed that the mangosteen peel polyphenol powder (MPP) had a high phenolic content of 154 mg gallic acid equivalent/g dry matter, which led to high 2,2-diphenyl-1-picrylhydrazyl free radical scavenging capacity of 95 mg Trolox equivalent/g dry matter. MPP also exhibited effective antimicrobial activity against E. coli and S. aureus, expressed by its large inhibitory zones (11.3 and 12.1 mm, respectively) and small ratios (less than 4) of minimum bactericidal concentration over minimum inhibitory concentration against tested bacteria. The MPP supplementation at the levels of 38 mg/100 g and 53 mg/100 g into fish balls remarkably improved their gel strength, reduced lipid oxidation, limited protein oxidation and structural degradation as compared to those of the control without any addition or with synthetic preservatives. Especially, the addition of 53 mg MPP/100 g could sufficiently retard the microorganism growth. The synergistic effects of MPP in both antioxidant and antimicrobial activities hence could extend the shelf-life of fish balls, more than 40 %, as compared to butylated hydroxytoluene (synthetic antioxidant) or sodium benzoate (synthetic antimicrobial) with their single effects. These findings imply that MPP could be potentially used as a natural additive in preservation of fish and meat products.