Resistance Profile of Listeria monocytogenes and Escherichia coli to High Power Ultrasound in Juice Matrices.

This study evaluated the resistance of Escherichia coli and Listeria monocytogenes to high power ultrasound (HPU) treatment under dynamic conditions in juice matrices. In addition, the effect of prior adaptation on microbial inactivation and the presence of injured population was assessed. Two strains each of L. monocytogenes and E. coli were subjected to HPU treatment under dynamic conditions (200 W, 14 mm probe diameter, and 3 cm immersion depth) for 360 s in four juices, namely carrot juice, tomato juice, pineapple juice, and coconut water. Strains were cultured in tryptone soy broth and tryptone soy broth supplemented with 1% (w/v) glucose to represent unadapted and acid-adapted conditions, respectively. Enumeration of the microbial concentration at selected time intervals was performed, while total microbial population and uninjured cells were differentiated. A one-step approach was used to model the survival curves and the result of the study shows that HPU treatment under dynamic conditions followed a non-log-linear behavior during microbial inactivation kinetics. More so, microbial reduction of at least 4-log in CFU/mL was attained regardless of the target strain or juice matrix. Furthermore, the obtained D-values and proportion of injured population were significantly dependent on strains and juice matrix. It was also observed that prior acid adaptation with glucose did not enhance the resistance of L. monocytogenes FBR 14 and E. coli FAM 21845 to HPU treatment under dynamic conditions in pineapple juice. The findings of this study are important for process optimization involving HPU-assisted processes specifically targeting juice matrices.