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.

中文翻译：

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通过生物富集硒增强纳豆激酶的热稳定性和抗氧化活性

通过在烧瓶培养物中进行液体发酵来生产纳豆激酶并富硒。为了优化目的，分析了不同浓度的Na ₂ SeO ₃（0、1、5、15、30、60和120 mg / L）。结果表明，添加了Na ₂ SeO ₃高达5 mg / L的显着性（P <0.05）促进了纳豆芽孢杆菌的生长并提高了蛋白酶活性。分析了富硒纳豆激酶（Se–NK）和非富硒纳豆激酶（NK）的pH值和热稳定性，这表明在中性和碱性pH（7–）下，NK和Se–NK均具有活性。酸性pH环境在最大水平下比碱性pH环境更严重地使酶失活，这表明纳豆激酶的氨基酸更碱性。在pH 8和45°C下，NK和Se–NK分别在258和342 min时保留了约50％的残留活性，这表明Se–NK的半衰期高于NK。此外，还评估了Se–NK和NK的抗氧化活性。结果表明，富硒纳豆激酶的抗氧化能力显着（P <0。05）高于未富集的纳豆激酶。因此可以得出结论，在发酵过程中富集硒可以提高纳豆激酶的稳定性和抗氧化活性，从而改善了纳豆激酶的整体状况。这项研究基本上描述了硒对新型蛋白酶纳豆激酶总体状态的影响。这将为商业上进一步安全富集纳豆激酶中的硒提供理论依据。