Antibacterial and hypoglycemic activity of flavonoids in etiolated tissues from fresh-cut Chinese water-chestnuts (Eleocharis tuberosa)

Chinese water chestnut (Eleocharis tuberosa) is prone to etiolation after fresh-cut treatment. Though etiolation caused undesired yellow color, it comes with accumulation of bioactive flavonoids. In this work, flavonoids were extracted from etiolated fresh-cut Chinese water chestnut. Their species and content were investigated. The antibacterial and hypoglycemic activities of crude extract were also characterized in vitro. The results showed that four main flavonoids naringenin, eriodictyol, quercetin and myricetin were identified from fresh-cut Chinese water chestnut and the content of total flavonoids greatly increased with the acceleration of etiolation. The antibacterial test showed that the flavonoid extract had significant inhibitory effect on Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Salmonella with the minimum inhibitory concentration of 2.5, 10, 2.5 and 5 mg/mL, respectively. The hypoglycemic kinetic analysis suggested that the flavonoid extracts exhibited competitive inhibition to both of α-glucosidase and α-amylase. The increased total flavonoids in extracts brought higher antibacterial and hypoglycemic ability during etiolation. These results revealed that the etiolated fresh-cut Chinese water chestnut can be developed and utilized for antibacterial and hypoglycemia activity.