Improve the Yield and Nutritional Quality of Sword Bean Oil With Solid-State Fermentation-Assisted Extraction Using Bacillus subtilis.

Sword bean, as a potential functional oilseed, is rich in multiple unsaturated fatty acids. This study aimed to establish a new solid-state fermentation-assisted extraction method for oil from sword beans with Bacillus subtilis ATCC 6051. The oil yield from sword beans fermented for 72 h (SBO-F) was 1.28% ± 0.07%, representing a 30.67% increase compared to unfermented sword bean oil (SBO). The physicochemical properties of SBO-F and SBO were analyzed. The results showed that SBO-F exhibited a significantly higher iodine value and a lower saponification value (P < 0.05), indicating increased unsaturation and a higher proportion of long-chain fatty acids. Gas chromatography-mass spectrometry analysis revealed that fermentation increased the unsaturated fatty acid content from 77.15% to 80.02% and generated two new unsaturated fatty acids, cis-10-pentadecenoic acid and erucic acid, that were not detected in SBO. Furthermore, the antioxidant activity of SBO-F was significantly enhanced. The IC50 value for the DPPH scavenging assay decreased from 2.01 ± 0.13 to 1.31 ± 0.11 mg/mL, for the ABTS+ scavenging assay from 14.38 ± 1.39 to 8.46 ± 0.33 mg/mL, and for the hydroxyl radical scavenging assay from 4.57 ± 0.06 to 3.97 ± 0.11 mg/mL. At a concentration of 5 mg/mL, the ferric-reducing antioxidant power increased from 262.15 ± 15.66 to 319.90 ± 8.54 µmol FeSO4/L. These results indicate that solid-state fermentation with B. subtilis is an effective and sustainable strategy that significantly improves the yield, nutritional quality, and antioxidant properties of sword bean oil, providing a theoretical basis for the development and utilization of sword bean as a functional oilseed.