Inactivation of Escherichia coli inoculated into cloudy apple juice exposed to dense phase carbon dioxide

Abstract

The inactivation of Escherichia coli in cloudy apple juice by dense phase carbon dioxide (DPCD) was investigated. With CO 2 at 20 MPa and 37 °C or at 30 MPa and 42 °C, the inactivation of E. coli significantly increased ( p < 0.05) when increasing the exposure time, which conformed to a fast-to-slow two-stage kinetics. The two stages were well fitted to first-order reactions. Higher temperature or pressure significantly enhanced the bactericidal effect of DPCD ( p < 0.05), the maximum reduction was 7.66 log CFU at 45 MPa and 52 °C for 30 min. The survival curves against temperature or pressure were fitted using a linear equation with high regression coefficients ( R 2 > 0.94). The temperature inactivation rate ( k T) and pressure inactivation rate ( k P) were obtained. Higher k T or k P indicated higher susceptibility of E. coli to temperature or pressure. Moreover, there was good linear correlation of k T with pressure ( R 2 = 1.00). Also, k P increased with increasing temperature except for 37 °C. Greater inactivation of E. coli was obtained with 99.9% CO 2 than with 99.5% CO 2 or with the initial number of 10 5 CFU/mL than with that of 10 8 CFU/mL at 20 MPa and 37 °C.