Effect of Mild Sonication Conditions on the Attributes of <i>Lactobacillus delbrueckii</i> ssp. <i>bulgaricus</i> LB-12

Abstract

Lactobacillus delbrueckii ssp. bulgaricus is a widely used bacterium for the production of some fermented dairy products. Mild sonication intensity condition is a non-destructive technique that uses sound waves to cause cavitation in aqueous solutions and may improve the permeability of membranes, speed up the transfer of substrates and promote cellular growth and propagation. The objective was to determine the effect of mild sonication intensities at different temperatures on growth, bile tolerance and protease activity of Lactobacillus delbrueckii ssp. bulgaricus LB-12. The treatments were four sonication intensities (8.07, 14.68, 19.83 and 23.55 W/cm 2 ) randomized at three different temperatures (4℃, 22℃ and 40℃). 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 2 h for 12 h of incubation. Protease activity was determined at 0, 12 and 24 h. Mild sonication conditions included 1) mild sonication intensities, 2) temperatures and 3) times, all three of which played a role in influencing the desirable attributes of Lactobacillus delbrueckii ssp. bulgaricus LB-12. Of all the mild sonication intensities studied, 14.68 W/cm 2 had the best overall influence at certain time points forimproving the bile tolerance and growth at 4℃ and protease activity at 40℃. Mild sonication intensity of 23.55 W/cm 2 had the best overall influence at certain time points for protease activity of at 22℃. Some mild sonication conditions could be recommended for improvement of some characteristics of Lactobacillus delbrueckii ssp. bulgaricus LB-12.