Production of Nattokinase from Hemp Seed Meal by Solid-State Fermentation and Improvement of Its Nutritional Quality

Abstract

Fermented foods have gained immense popularity in recent years due to their distinct flavor profile. Given the increasing demand, there is a growing focus on optimizing their nutritional quality while also reducing their costs. In this study, using a novel approach, hemp seed meal was utilized as a solid fermentation substrate to produce nattokinase (NK). Using a combination of one-factor-at-a-time experiments, Plackett–Burman design, and Box–Behnken design, the optimal fermentation conditions of Bacillus subtilis 13932 (NK-producing strain) were determined. The initial ratio of HSM (hemp seed meal) to water was 1:2.0 (v:w), the thickness of the substrate was 2.9 cm, the bacterial inoculum volume was 10% (v:w), the relative humidity was 75.2%, the temperature was set at 35 °C, and the fermentation time was 20 h. The NK activity under these conditions was measured to be 7067.12 IU/g. During fermentation, 15.15% of soluble peptides were produced, which exhibited hydroxyl radical removal ability and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical removal ability of 14.85%, down from 32.96%. Furthermore, trypsin inhibitor and urease in HSM decreased by 42.6% and 73.6%, respectively, improving the nutritional quality of HSM. Sensory evaluations indicated that HSM is expected to be a popular food, highlighting the potential of using HSM as a solid fermentation substrate for NK production.