Stimulating fermentative activities of bifidobacteria in milk by highintensity ultrasound

The effect of ultrasonic processing at 20 kHz on the fermentative activities of four different strains of Bifidobacterium (i.e., Bifidobacterium breve ATCC 15700, Bifidobacterium infantis, Bifidobacterium animalis ssp. lactis (BB-12), and Bifidobacterium longum (BB-46)) in milk was investigated. Results showed that ultrasound under the applied conditions could reduce the fermentation time required to reach pH 4.7 for samples with B. infantis, B. breve ATCC 15700, and BB-12, but not for BB-46. The viability of each the first three strains at the end of the fermentation was comparable with that of the corresponding control. The probiotic bacteria cells were ruptured by ultrasound and released intracellular enzyme β-galactosidase that promoted the hydrolysis of lactose and trans-galactosylation, and subsequently enhanced the growth of the remaining bacterial cells in inoculated milk during fermentation. The lower the concentration of lactose, the higher the amount of oligosaccharides (degree of polymerization = 3) found in the fermented milk with ultrasound treatment.