Functional component and antioxidant activity analysis of banana stem juice fermentation products

【Objective】To explore functional components and antioxidant capacities of banana stem juice fermentation products, so as to provide theoretical support for the development and utilization of functional products of banana stem juice.【Method】Banana stem juice was used as raw material. Different types of bacteria agents，such as K1 and Kefir （KF），were used for fermentation. Fermented products，including lactic acid beverages（KF100 and KF50）and wine （K100 and K50），developed from different percentages of banana stem juice（100% and 50%），were analyzed for selected functional components（polyphenols，tannins，and total flavonoids），antioxidant capacities（DPPH free radical clearance ability，hydroxyl radical inhibition ability，superoxide anion free radical inhibition ability，and metal chelation rate）and nitrite content. Differences in these chemical components and antioxidant capacities were compared among the banana stem juice fermentation products. The data were also evaluated based on the principal component analysis.【Result】Polyphenolic and tannin content of banana stem juice fermentation products were higher than that of unfermented banana stem juice whose polyphenolic and tannin contents were 3.05 mg/g and 37.9 mg/kg，respectively. Flavonoids were not detected in these samples. Comparing the fermentation products fermented by different percentages of banana stem juice，polyphenolic and tannin contents of KF100 were 24.7% and 10.3%，respectively，higher than that of KF50. Polyphenolic and tannin contents of K100 were also 18.7% and 32.2% higher than that of K50，respectively. Among the same banana stem juice fermentation products，polyphenolic content of KF50 and KF100 were 16.3% and 12.0% lower than that of K50 and K100，respectively. Tannin content of KF50 and K100 were 87.5% and 56.4% higher than that of the K50 and K100， respectively. DPPH clearance ability，hydroxyl radical inhibition ability，and of superoxide anion free radical inhibition ability of the banana-stem-juice-fermented wine were higher than the fermented lactic acid beverage. Metal chelation rate of KF100 was also the highest. The result of the principal component analysis showed that K50 had the highest comprehensive evaluation value of the antioxidant activity index. The nitrite content of KF100 was high，reaching 2.3 μmol/L， whereas the nitrite content of the other three samples was lower than 0.5 μmol/L.【Conclusion】Banana stem juice fermentation products have certain free radical scavenging ability and high metal-chelating effect. The K50 had the highest antioxidative properties. These data can provide a theoretical basis for future development of healthy banana-stem-juice-fermented products.