Synergistic effect of ultrasonic waves under pressure at mild temperatures (MTS) in yeast inactivation

Ultrasonic treatments are one of the new technologies for microbial inactivation that could serve as an alternative for food preservation. However, decimal reduction times for most of microbial species generally exceed 1 min. Therefore, combined processes have been designed, based on the simultaneous application of ultrasonic waves under pressure at moderate temperatures (mano-thermo-sonication process, MTS). The aim of this study was mathematically quantify the synergism of MTS treatments on S. bayanus and different microbial groups including vegetative cells and bacterial spores and compare them. Results show that the lethal effect of MTS treatments may have both, additive (A. hydrophila, Y. enterocolitica) or synergistic effect (S. bayanus, L. monocytogenes, Salmonella spp., Bacillus spp.). The synergistic effect increases with temperature until reaching a maximum and then descending. A big synergistic effect was observed in yeasts and bacterial spores while lower synergy was observed in bacterial vegetative cells. The more heat resistant bacterial species showed higher synergistic effect of the MTS treatments.