In situ Raman quantification of the dissolution kinetics of carbondioxide in liquid solutions during a dense phase and ultrasoundtreatment for the inactivation of Saccharomyces cerevisiae
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In this work, a Raman based optical approach is presented that enables remote, real time and in situ quantification of the amount of carbon dioxide (CO2) dissolved in distilled water and coconut water during a dense phase carbon dioxide (DPCD) and a combined dense phase carbon dioxide and ultrasound (DPCD + US) pasteurization. CO2 dissolution kinetics were measured in an optically accessible high pressure cell at different temperatures (25, 35, 40 °C) and pressures (8 and 12 MPa). Two different mixing devices (mechanical and magnetic) during DPCD treatment, and different ultrasound powers (10, 20, 30 W) during the DPCD + US treatment were applied. The dissolution data were then related with the inactivation ratio of Saccharomyces cerevisiae inoculated into the solutions. The results demonstrated that an increase of pressure or time during DPCD treatment enhances the amount of CO2 dissolved into the liquid, leading to a higher inactivation degree; the same trend was observed when the temperature was increased, although in this latter case, the amount of dissolved CO2 decreased. The increase of pressure during a combined DPCD + US treatment led to a higher amount of dissolved CO2, which positively influenced the microbial inactivation while no effect was obtained increasing the ultrasound power. Concerning the effect of the mixing devices, the mechanical stirrer was the one that enhanced the pasteurization efficiency as it influenced CO2 dissolution kinetics and, consequently, the microbial inactivation ratio. The composition of the liquid solutions also influenced the amount of dissolved CO2 but no correlations were found with S. cerevisiae inactivation.