In Situ Raman Quantification Of Dissolution Kinetics Of Carbon Dioxide In Liquid Solutions During A High Pressure And Ultrasound Treatment For The Inactivation Of Saccharomyces Cerevisiae
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A Raman based optical approach is presented to enable the remote, temporally resolved and in situ quantification of the amount of carbon dioxide (CO2) dissolved in distilled water and coconut water during a high pressure (HPCD) and a combined high pressure high power ultrasound (HPCD+HPU) pasteurization. The CO2 dissolution kinetics were measured in an optically accessible high pressure cell at different temperatures (25, 35, 40 °C), pressures (8 and 12 MPa), and time instants after pressurization of the liquid solution with CO2 (10, 30, 60 min). Two different mixing devices (mechanical and magnetic) during HPCD treatment and different ultrasound powers (10, 20, 30 W) for the HPCD+HPU treatment were applied. The dissolution data were then related with the inactivation degree of Saccharomyces cerevisiae inoculated into the solutions at the same process conditions. The results demonstrate that an increase of pressure or time during HPCD treatment enhances the amount of CO2 dissolved into the liquid, leading to a higher inactivation degree; the same trend in inactivation was observed when the temperature was increased although, in this latter case, the amount of dissolved CO2 was decreased. The increase of pressure during HPCD+HPU combined treatment led to a higher amount of dissolved CO2, which positively influenced the microbial inactivation while no effect was obtained increasing the ultrasound power. Furthermore, the choice of the mixing device was demonstrated to be one of the key parameters to enhance the pasteurization process efficiency as it influenced CO2 dissolution kinetics and, consequently, the microbial inactivation rate. The composition of the liquid solutions also influenced the amount of dissolved CO2 but no correlations were found with S. cerevisiae inactivation.