Influence of three ultrasound treatments on viability, culturability, cell architecture, enzymatic activity and metabolic potential of Lacticaseibacillus paracasei 90

The effects of ultrasonic bath (UB) and ultrasonic probe (UP) treatments on culturability, viability, cell architecture, and enzymatic activity of Lacticaseibacillus paracasei 90 (L90) were studied by cell count, flow cytometry, scanning electron microscopy (SEM) and enzyme activity determinations. To evaluate the metabolic potential of the treated cells, milk was inoculated with treated or untreated bacteria, and incubated for 20 h at 37 °C. SEM revealed cellular damage in some UP-treated cells; flow cytometry and enzyme activity analysis reflected an overall increase in permeability and lysis. UB increased the proteolytic activity of L90 and reduced its ability to produce acid. The damage of the cellular integrity caused by UP led to an increase in enzyme accessibility to the substrate, positively correlated with enhanced diacetyl and acetoin production. Depending on equipment used and exposure time, ultrasonic waves may be used to enhance the metabolic potential of starter and adjunct cultures.