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International Journal of Food Microbiology
j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / i j f o o d m i c r o
Behavior of inactivation kinetics of Escherichia coli by dense phase carbon dioxide
Hongmei Liao, Yan Zhang, Xiaosong Hu, Xiaojun Liao ⁎, JihongWu
Research Centre for Fruit and Vegetable Processing Engineering, College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
A R T I C L E
I N F O
A B S T R A C T
Inactivation of Escherichia coli in cloudy apple juice by dense phase carbon dioxide (DPCD) was investigated. The pressures were 10, 20 and 30 MPa, the temperatures were 32, 37and 42 °C. The inactivation kinetic behavior of E. coli conformed to a sigmoid curve with a shoulder and a tail, which was closely related with temperature or pressure. With the increase of temperature or pressure, the shoulder became unclear or even disappeared. The experimental data were well ﬁtted to a model proposed by Xiong et al. [Xiong, R., Xie, G., Edmondson, A.E., Sheard, M.A., 1999. Amathematical model for bacterial inactivation. International Journal of Food Microbiology 46, 45–55], the kinetic parameters of tlag (the lag time length), f (the initial proportion of less resistant population), k1 (the inactivation rate constant of less resistant fraction) and k2 (the inactivation rate constant of resistant fraction), and t4 − D (the time required for an 4-log-cycle reduction ofbacteria under a given condition) were obtained from this model. The tlag declined from 4.032 to 0.890 min and t4 − D from 54.955 to 18.840 min, k1 was 1.74–4.4 times of k2. Moreover, the model was validated by more experimental data, the accuracy factor (Af), bias factor (Bf), root mean square error (RMSE), sum of squares (SS), and correlation coefﬁcient (R2) were used to evaluate this modelperformance, indicating that the model could provide a good ﬁtting to the experimental data. © 2008 Elsevier B.V. All rights reserved.
Article history: Received 13 October 2007 Received in revised form 6 May 2008 Accepted 8 May 2008 Keywords: Dense phase carbon dioxide Escherichia coli Inactivation Apple juice Model
1. Introduction Thermal pasteurization of juices may lead to a loss of ﬂavor,color and nutrients which has increased interests in non-thermal pasteurization of juices. Various studies have shown that dense phase carbon dioxide (DPCD) can be an effective means to inactivate microorganisms (Haas et al., 1989; Balaban et al., 1993; Ishikawa et al., 1997; Osajima et al., 1998; Dillow et al., 1999; Hong and Pyun, 2001; Spilimbergo and Bertucco, 2003; Lecky, 2005; Kincal et al.,2005; Damar and Balaban, 2005), The microbial inactivation induced by DPCD is affected by pressure, temperature, exposure time, pH, and so on (Damar and Balaban, 2006). Four of the most common survival curves of microbial inactivation were observed as followed in earlier investigations: linear curves, curves with a shoulder, curves with a tailing and sigmoidal curves, and they could be analyzed byﬁrst order kinetics, Buchanan model, Cerf's model and Whiting–Buchanan model, respectively (Chick, 1908; Cerf, 1977; Buchanan et al.,1993; Cole et al.,1993; Whiting et al.,1996; Xiong et al., 1999). Some more predictive models are also used to describe the survival curves of microbial inactivation, such as Cole model, Gompertz model, Logistic model, Kumau model (Kumau et al., 1990; Cole et al., 1993;Bozkurt and Erkmen, 2001). The behavior of inactivation kinetics induced by DPCD showed three modes in previous studies: linear, slow-to-fast two-stage and fast-to-slow two-stage (Ballestra et al., 1996; Debs-Louka et al., 1999; Erkmen and Karaman, 2001). Linear
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