Comparison of Peptide Yield and Antihypertensive Activity from Hemp Protein Isolate Fermented by Three Bacillus Strains

This study aimed to optimize the fermentation conditions for hemp protein isolate (HPI) via liquid-state pure culture fermentation using three Bacillus strains (Bacillus subtilis natto, Bacillus subtilis, and Bacillus licheniformis) with peptide yield as the key index, and further to evaluate the antihypertensive potential of the fermented HPI in vitro and in vivo. Orthogonal experiments identified the optimal fermentation conditions for Bacillus subtilis natto: 4% inoculation size, initial pH 8.0, 96 h fermentation, and 1:10 (g/mL) HPI-to-water ratio, yielding a maximum peptide content of 32.30%, significantly higher than that of Bacillus subtilis (14.76%) and Bacillus licheniformis (19.55%). Fermentation markedly enhanced the antihypertensive activity of HPI: oral gavage of Bacillus subtilis natto-fermented products in hypertensive rats exhibited antihypertensive effects comparable to captopril (positive control), reducing systolic, diastolic, and mean blood pressures after 3 weeks (high dose) and 4 weeks (low dose). In contrast, the other two strains showed superior angiotensin-converting enzyme (ACE)-inhibitory activity (Bacillus subtilis: 81.77%; Bacillus licheniformis: 63.95%) compared to Bacillus subtilis natto (58.89%). Collectively, Bacillus subtilis natto is the most effective strain for enhancing HPI’s in vivo antihypertensive activity, providing a critical foundation for developing fermented HPI as a nutraceutical for hypertension management.