Ultrasound-assisted supercritical CO2 treatment in continuous regime: Application in Saccharomyces cerevisiae inactivation

• An ultrasound assisted continuous supercritical CO2 pasteurization system was built.
• Continuous SC-CO2 juice flow treatment greatly enhanced microbial inactivation.
• Ultrasound considerably intensified inactivation using the continuous system.
• 7.8 log-cycles inactivation obtained after 9.2 min residence time (300 bars; 31 °C).
• Optimal process conditions were established through multivariate optimization.

Laboratory continuous regime equipment was designed and built for supercritical CO2 microbial inactivation assisted by high power ultrasound (SC-CO2-HPU). Apple juice, previously inoculated with 1–10 × 107 CFU/ml of Saccharomyces cerevisiae, was treated in the equipment at different juice residence times (3.06–9.2 min), temperatures (31–41 °C) and pressures (100–300 bars). Inactivation ratios were fitted to a hybrid (boolean-real) model in order to study the effect of the process variables. The maximum inactivation achieved by the system was 7.8 log-cycles. The hybrid model demonstrated that HPU has a significant effect on inactivation after shorter residence times. A multi-objective optimization performed with the hybrid model showed that 6.8 log cycles of inactivation could be obtained after a minimum residence time (3.1 min) with HPU application, whereas under the same conditions but without HPU, the inactivation would be 4.3 log-cycles. Therefore, the ultrasound assisted continuous system has shown a great potential for microbial inactivation using SC-CO2 under mild process conditions.