α-Galactosidase and proteolytic activities of selected probiotic and dairy cultures in fermented soymilk

The metabolic activities of Lactobacillus acidophilus (LAFTI® L10 and La4962) Bifidobacterium (lactis LAFTI® B94 and longum Bl536), Lactobacillus casei (LAFTI® L26 and Lc279), Lactobacillus delbrueckii ssp. bulgaricus Lb1466 and Streptococuss thermophilus St1342 were assessed in soymilk. Strains were initially analyzed for α-galactosidase activity and organic acid production in MRS broth at 37 °C. Consequently, soymilk was fermented with each strain and cell growth, production of organic acid, metabolism of oligosaccharides and proteolytic and ACE-inhibitory activities were assessed during 48 h of incubation at 42 °C. All strains exhibited variable α-galactosidase activity, with Bifidobacterium lactis B94 showing the highest activity. The oligosaccharide metabolism depended on α-galactosidase activity. B. lactis B94, S. thermophilus St1342 and L. acidophilus La4962 reduced raffinose substantially by 77.4%, 64.5% and 55.9%, respectively. All strains reached the desired therapeutic level of 108 cfu/ml in soymilk after 48 h at 42 °C. The hydrolysis of protein in soymilk likely depended on strain (P < 0.0001) and time (P < 0.0001). The strains also released bioactive peptides with ACE-inhibitory activities between 17% and 43%.