High power ultrasound combined with supercritical carbon dioxide for the drying and microbial inactivation of coriander

This work explores the use of supercritical carbon dioxide (scCO2) drying in combination with High Power Ultrasound (HPU) to enhance both the dehydration efficiency and the microbial inactivation on coriander leaves. ScCO2 drying process alone was compared with a combined drying process (HPU + scCO2) at different powers (10, 40 and 80 W), different drying times (up to 90 min) and two process temperatures (40 and 50 °C). At the most effective condition tested (40 W; 10 MPa; 40 °C), mesophilic bacteria were reduced up to 4 Log, mesophilic spores up to 1 Log, while yeast and molds were never detected (< 2 log CFU/g). 40 W was identified as the threshold HPU value to achieve a beneficial effect on mesophilic bacterial spores reduction. Besides, the use of HPU enhanced the water loss and lowered the water activity of the samples, compared to the ones processed with scCO2 alone. The appearance and color of the dried samples did not show significant differences after the two processes. Overall, HPU + scCO2 process resulted a promising technology to enhance both the dehydration and microbial inactivation efficiency compared to scCO2 drying alone.