Lactose hydrolysis and β-galactosidase activity in sonicated fermentation with Lactobacillus strains

Milk fermentation with four Lactobacillus strains, including L. delbrueckii subsp. bulgaricus B-5b, L. helveticus LH-17, L. delbrueckii subsp. lactis SBT-2080 and L. acidophilus SBT-2068, was carried out under sonicated conditions. Under continuous sonication, viable cell count decreased or grew less than in conventional fermentation, but it increased considerably in static incubation after sonication. Sonication caused β-galactosidase release from lactic acid bacteria cells to the culture medium, thus resulting in higher total β-galactosidase activity. However, lactose hydrolysis was enhanced only when β-alactosidase was effectively released. With L. delbrueckii subsp. bulgaricus B-5b and L. helveticus LH-17, the degrees of lactose hydrolysis achieved were about 75% which is much higher than those in conventional fermentation (below 40%). Results presented here showed that a high viable cell count and a high degree of lactose hydrolysis could be simultaneously achieved by a suitable sonication method.