An ultrasound-enhanced system for microbial inactivation using supercritical carbon dioxide

Abstract

Abstract The effect of ultrasound on the SC-CO 2 inactivation kinetics of E. coli at different pressures (100, 225, 290 and 350 bar; 36 °C), temperatures (31 °C, 36 °C and 41 °C; 225 bar) and varying the composition of the medium (LB Broth, apple and orange juice) was studied. Using only SC-CO 2 the inactivation rate in LB Broth increased progressively as the pressure or temperature rose and the average (for the different process conditions) time needed to achieve a reduction of 8 log-cycles was 50 min. When both SC-CO 2 and ultrasound were used in LB Broth, 95% less time was needed, on average, to achieve the same reduction of 8 log-cycles and the effect of pressure and temperature was minimized; this reduction being achieved after only 2 min at 31 °C and 225 bar. Using the ultrasonic system led to a shorter process time regardless of the treatment medium, preventing the inhibitory effect that the solutes from the juices had on the SC-CO 2 inactivation. The technology developed permits both a drastic decrease in SC-CO 2 inactivation times and also the use of mild process conditions, which could lead to an increase in the quality of the product treated under this new technique. Industrial Relevance Supercritical carbon dioxide (SC-CO 2 ) inactivation technology represents a promising nonthermal processing method, although a too long treatment time is required to guarantee food safety. A patented inactivation technique based on Supercritical Fluids incorporating an ultrasonic transducer is presented. A drastic decrease of the inactivation time is found when high power ultrasound is applied to the SC-CO 2 inactivation process coupled with the food industry’s need for short process times. The inactivation process is improved regardless of the pressure, temperature or treatment medium. Therefore, mild process conditions (time, pressure, temperature) can be used, which result in a higher quality treated product.