Antihypertensive peptides and γ-aminobutyric acid from prozyme 6 facilitated lactic acid bacteria fermentation of soymilk

Soymilk was fermented with five lactic acid bacteria (Lactobacillus casei, Lactobacillus acidophilus, Streptococcus thermophilus, Lactobacillus bulgaricus, Bifidobacterium longum) for up to 30 h at 42 °C. A protease, prozyme 6, was added 5 h after fermentation. The whey was separated from the fermented soymilk and then freeze-dried. As the fermentation time extended to 30 h, pH decreased from 6.5 to 4.1, soluble protein content increased from 47 to 390 mg/g, free amino acid content increased from 91.3 to 214.4 mg/g, peptide content increased from 39.6 to 463.3 mg/g and γ-aminobutyric acid (GABA) increased from 93.9 to 361.6 mg/100 g, and inhibition of angiotensin I-converting enzyme (ACE) IC50 decreased from 9.28 to 0.66 mg powder/ml, respectively. Fermentation of whey for 30 h was fractionated by size exclusion chromatography on a Sephadex G-15 column. A fraction of 800–900 Da was found with the highest inhibitory efficiency ratio (IER) being 795%/(mg ml). This whey (peptide concentration 10 mg/ml) was used as drinks administered to the spontaneously hypertensive rat (SHR) for 8 weeks. The systolic blood pressure (SBP) of SHR reduced to 19.0 mmHg after 8 weeks of oral administration.