Impact of high-intensity ultrasound on fermentation, viability and predictive growth of lactic acid cultures: A study with conventional and probiotic fermented milks

This study assessed the effect of high-intensity ultrasound on fermentation, viability, and microbial behavior of starter cultures in fermented milk. First, the direct (probe) and indirect (bath) ultrasound effects were studied. Three energy densities (1600, 640, and 200 J mL-1) were tested on milk fermentation and dairy culture viability (conventional and probiotic) for these experiments. Secondly, after probe ultrasound treatment, the microbial behavior and the pH were evaluated during the fermentation. Furthermore, the microbial growth parameters were estimated by a predictive model. The indirect application of high-intensity ultrasound baths at different energy densities and temperatures did not show significant changes. Nevertheless, the probe ultrasound treatments with the density of 640 and 200 J mL-1 revealed a reduction in the fermentation time of milk fermented with the traditional yogurt culture and only with the probiotic, respectively. According to the predictive modeling, when the ultrasound was applied to the cultures separately, there was an improvement in the microbial growth rate. Therefore, using probe ultrasound separately to milk fermented with only traditional yogurt cultures (Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus) or only with Lactobacillus acidophilus LA -5 using energy density of 640 and 200 J mL-1 becomes more attractive.