THE EFFECT OF HIGH INTENSITY ULTRASOUND TREATMENT ON PROBIOTIC STARTER CULTURE

Abstract

This research investigated the effect of high-intensity ultrasound (HIU) treatment (20 kHz) on Streptococcus thermophilus and Lactobacillus delbrueckii subspecies bulgaricus when mono- or co-cultured in skim milk. Higher sonication intensity increased the percentage of killed starter culture, which was higher for rod-shaped than cocci cells. On the other hand, short exposure of S. thermophilus to sonication waves produced yoghurt in up to 7.8% shorter time when compared to the control. Samples reaching pH 4.70 the fastest were those containing the highest microbial content and showed increased lactic acid production. Simultaneous sonication of seed starter culture shortened yoghurt production when treated for 3 min (A40%) by 6.0 - 7.6 %. Moreover, prolonged exposure to HIU resulted in substantial extraction of β-galactosidase for both yoghurt starter cultures regardless if in mono- or co-culture, which increased the degree of lactose consumption, making fermented milk more susceptible for lactose intolerant consumers.