Influence of "Mild" Sonication Conditions on the Characteristics of Streptococcus thermophilus ST-M5

Mild sonication intensity is an acoustic energy which involves the conversion of electrical signal into a physical vibration modifying the permeability of the cell plasma membrane. The objective of this study was to determine the effect of mild sonication intensities at different temperatures on growth, bile tolerance and protease activity of Streptococcus thermophilus. The treatments were four mild sonication intensities (8.07, 14.68, 19.83 and 23.55 W/cm2) randomized at three different temperatures (4°C, 22°C and 40°C). The energy input (1500 J) was kept constant in all treatments. Control samples did not receive any sonication treatment. Growth and bile tolerance were determined every two hours for 12 h of incubation. Protease activity was determined at 0, 12 and 24 h. Mild sonication conditions included a) mild sonication intensities, b) temperatures and c) times, all three of which played a role in influencing the desirable attributes of Streptococcus salivarius ssp. thermophilus ST-M5. Of all the mild sonication intensities studied, 14.68 W/cm2 had the best overall influence at certain time points for improving bile tolerance and growth at 4°C, growth at 22°C and bile tolerance and growth at 40°C of Streptococcus salivarius ssp. thermophilus ST-M5. Mild sonication intensity of 23.55 W/cm2 had the overall best influence at certain time points for protease activity of Streptococcus salivarius ssp. thermophilus ST-M5 at 40°C. Streptococcus thermophilus ST-M5 pretreatment with some mild sonication conditions can be recommended for improvement of some of its characteristics.