Effect of sonication on microwave inactivation of Escherichia coli in an orange juice beverage

Abstract

The survival of Escherichia coli ATCC 25922 in orange juice treated with microwave and/or ultrasound was evaluated; Weibull model was fitted to survival curves to describe inactivation kinetics; and the effect of combined microwave-ultrasound treatments was assessed. Ultrasonic treatment (42 kHz) has no significant effect on the survival rate reduction (1.3 log for 60 min of sonication) of E. coli. However, sonication can increase the efficiency of microwave inactivation. The use of ultrasound as pre-treatment was more effective than when used in post-treatment, that is, a reduction of 8.0 log was achieved by a combination of ultrasound (20 min) followed by a microwave (900 W/30 s), while 4.0 log was obtained when these both processes were reversed. The scale parameter α estimated from microwave-inactivation kinetics combined with an ultrasound pre-treatment was found to be lower than those obtained with a post-treatment, which, in turn, are lower than those estimated for microwave or ultrasound alone. These results demonstrate the effectiveness of ultrasound as a pre-treatment to improve the inactivation of E. coli by microwave processing in orange juice beverages.