Enhanced thermostability and antioxidant activity of Nattokinase by biogenic enrichment of selenium

Abstract

Nattokinase was produced and enriched with selenium by liquid fermentation in a flask culture. Different concentrations of Na2SeO3 (0, 1, 5, 15, 30, 60 and 120 mg/L) were analysed for optimization purpose. Results demonstrated that addition of Na2SeO3 up to 5 mg/L significantly (P < 0.05) facilitated the growth of Bacillus Natto and improved the protease activity. The pH and thermostability of selenium enriched nattokinase (Se–NK) and non-enriched nattokinase (NK) were analysed which indicated that at neutral and alkaline pH (7–), both NK and Se–NK were active. The acidic pH environment de-activated enzyme more severely than alkaline pH environment at maximum level which indicated that the amino acids of nattokinase were more basic. At pH 8 and 45 °C about 50% of residual activity was retained by NK and Se–NK at 258 and 342 min respectively which shows that half-life of Se–NK is higher than NK. Furthermore antioxidant activities of Se–NK and NK were evaluated. Results showed that the antioxidant capacity of selenium enriched nattokinase was significantly (P < 0.05) higher than non-enriched nattokinase. Hence it was concluded that selenium enrichment during fermentation process improved the overall status of nattokinase by improving its stability and antioxidant activities. This study basically described the selenium effect on overall status of a novel protease enzyme nattokinase. It will provide theoretical basis for further safe enrichment of selenium in nattokinase on commercial level.