Antioxidant and antimicrobial properties of grape and papaya seed extracts and their application on the preservation of Indian mackerel (Rastrelliger kanagurta) during ice storage

Antioxidant properties of grape (GSE) and papaya seed extracts (PSE) were tested in vitro at varied concentrations and growth inhibition were seen against gram positive and gram negative bacteria by disc diffusion method. The results revealed that GSE contain four times higher phenolic and six folds higher flavonoid content than PSE. The antioxidant properties of GSE and PSE showed dose dependent activities and were comparatively much higher in GSE. Linoleic acid model of GSE and PSE displayed 67.67 and 46.43 % of inhibition respectively at 500 mg/L. The effect of dip treatment by GSE and PSE at a concentration of 500 and 1000 mg/L respectively on the quality changes of Indian mackerel (Rastrelliger kanagurta) in iced condition were assessed using chemical, microbiological and sensory parameters along with chilled whole control (CWC). The inhibition of primary and secondary lipid oxidation products by GSE at 500 mg/L was comparable to BHT at 200 mg/L. GSE exhibited higher antimicrobial activity on gram-positive strains compared to PSE and reduced the formation of volatile bases significantly. On the day of sensory rejection for CWC, the formation of trimethylamine and total volatile base nitrogen were reduced by 32.27 and 31.85 % in GSE samples and 19.01 and 24.70 % in PSE samples respectively. The dip treatment of GSE increased the shelflife of mackerel up to 15 days, PSE by 12 and 9 days for CWC during ice storage. Therefore, it can be concluded that, GSE can be used as a promising natural preservative and a substitute to the synthetic counterparts.