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The effect of ultrasound (HPU) on the supercritical carbon dioxide (SC-CO2) inactivation of vegetative bacteria (Escherichia coli, Brevundimonas diminuta) and a fungal spore (Aspergillus niger) at different pressures (100 and 350 bar) and temperatures (35, 50 and 60 °C) was assessed. The effect of SC-CO2 + HPU on the microbial cell ultrastructure was also evaluated by microscopy techniques (FESEM and TEM). HPU enhanced the SC-CO2 inactivation treatments, showing an average increase of 4.8, 3.4 and 1.3 log-cycles of reduction for E. coli, B. diminuta and A. niger, respectively. In general, the higher the pressure and temperature, the higher the inactivation. A. niger spores were found to be more resistant than vegetative bacteria. Microscopy analysis revealed significant morphological changes, including damaged cell walls, and major alteration and loss of cytoplasmic content. Therefore, the SC-CO2 + HPU technology appears to be effective for microbial inactivation purposes despite the complexity of the cell wall. |
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