Inactivation kinetics and cell morphology of E.coli and S.carevisiae trated with ultrasound-assited supercritical CO2

Abstract

[EN] The inactivation kinetics of Escherichia coli (E. coli) and Saccharomyces cerevisiae (S. cerevisiae) cells in apple juice subjected to supercritical carbon dioxide (SC-CO2) assisted by high power ultrasound (HPU) at different pressures (100 350 bar, 36 °C) and temperatures (31 41 °C, 225 bar) were studied. On average, shorter process times were required to achieve the total inactivation of S. cerevisiae (2 6 min) in apple juice than E. coli (7 min). The inactivation kinetics of E. coli and S. cerevisiae were satisfactorily described by the Peleg Type A and theWeibull model, respectively, considering temperature and pressure as model parameters. Transmission electron microscopy (TEM) and light microscopy (LM) techniques were used to study the cellular changes of SC-CO2 (350 bar, 36 °C, 5 min) and SC-CO2+HPU (350 bar, 36 °C, 5 min, 40W)treated cells. TEMand LMimages revealed that 5 min of SC-CO2 treatment generated minor morphological modifications, although no inactivation of the cells was obtained. However, 5 min of SC-CO2+HPU treatment totally inactivated the population of both microorganisms. SC-CO2 + HPU produced the degradation of the internal cell content and the disruption of the cell wall and plasmalemma, which prevented the possible regrowth of the cells during refrigerated storage.