Response of Saccharomyces cerevisiae to the combined action of ultrasound and low weight chitosan

The resistance of Saccharomyces cerevisiae to the action of ultrasound (600 W, 20 kHz, 95.2 μm wave amplitude) at 45 °C in Sabouraud broth (pH 5.6) containing 1000 ppm low weight chitosan was analyzed. Preincubation of the inoculated systems 30 and 90 min prior to sonication was also evaluated. Addition of chitosan enhanced the inactivation by ultrasound. Incubating the yeast with chitosan prior to sonication increased the inactivation. After 30 min of exposure to chitosan, approximately 1-log cycle reduction of the yeast was obtained leading to a final reduction of more than three log cycles after 30 min of the ultrasonic treatment. Ninety minutes of exposure to chitosan resulted in little significant change in yeast reduction. Transmission electron microphotographs of the cells showed possible different action mechanisms of chitosan depending on whether systems were preincubated or not. Experimental data were modeled by using the modified Gompertz equation and Weibull distribution of resistances.