Production of nattokinase and γ-polyglutamic acid via soybean whey fermentation by Bacillus subtilis BSNK-5 and their emulsification to form nanoemulsions

Soybean whey, a nutrient-rich byproduct generated during the production of soybean protein isolate, can only be discharged after undergoing sewage treatment, which imposes a significant economic burden on enterprises. In this study, we investigated a Bacillus subtilis BSNK-5 fermentation soybean whey process that yielded high production of nattokinase (NK) and γ-polyglutamic acid (γ-PGA), along with the fabrication of an emulsion using fermentation soybean whey, to achieve high-value conversion of soybean whey. The results showed that soybean whey can be used as a nutrient-rich substrate to promote the efficient synthesis of NK and γ-PGA by BSNK-5, with the highest yields of 9 × 10 4 IU/mL and 250 g/L, respectively. Meanwhile, the synthesized γ-PGA can serve as a suitable biological macromolecule to form an emulsification system that protects NK. The encapsulation efficiency of NK was over 60%, and the release of encapsulated NK was delayed in vitro . Meanwhile, the nanoemulsions remained stable when exposed to 37°C and 65°C temperatures, salt concentrations ranging from 50-150 mM, and undergoing a single freeze-thaw cycle. The development of functional thrombolytic preparations by self-emulsification protection of NK by γ-PGA produced via BSNK-5 fermentation represents an effective way to achieve high value utilization of soybean whey. • The soybean whey was fermented using BSNK-5 to produce NK and PGA • The NK content was highest after 48 hours of fermentation • The nanoemulsions was successfully fabricated using fermentation soybean whey • The nanoemulsion with SSG and 10% Tween 80 was the most stable • The NK encapsulated in nanoemulsions enabled slow-release in vitro digestion