Submitted to: Ozone Science and Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/21/2015
Publication Date: 8/20/2015
Citation: Devatkal, S.K., Jaiswal, P., Kaur, A., Juneja, V.K. 2015. Inactivation of Bacillus cereus and Salmonella enterica serovar Typhimurium by aqueous ozone (O3): Modeling and Uv-Vis spectroscopic analysis. Ozone Science and Engineering. doi: 10.1080/01919512.2015.1079119. Interpretive Summary: Ozone, an alternative non-thermal food preservation technology, has been used in the food industry to process foods with minimal negative impact on product quality. We assessed the efficacy of aqueous ozone on destruction of deadly foodborne pathogens, Salmonella enterica Typhimurium and Bacillus cereus. Destruction of pathogens was found to be a function of time and the inactivation times for a 4 log cycle reduction ranged between 9.14 and 4.51min for B.cereus and S. Typhimurium, respectively. The predictive models developed will assist the food industry and regulatory agencies to design processes to guard against foodborne pathogens, Bacillus cereus and Salmonella enterica Typhimurium.
Technical Abstract: Ozone (O3) is a natural antimicrobial agent with potential applications in food industry. In this study, inactivation of Bacillus cereus and Salmonella enterica Typhimurium by aqueous ozone was evaluated. Ozone gas was generated using a domestic ozone generator with an output of 200 mg/hr (approx. 0.1 mg/l). Buffer solutions (PBS) containing known amounts (approx.108-109 cfu/ml) of bacterial pathogens were treated with aqueous ozone for 16 min with sampling at 0, 0.5,1,2,4,8 and 16 min intervals. Inactivation kinetics was studied using GInaFiT tool and suitable inactivation models were identified. Uv-Vis spectroscopy and chemometric analysis was also used to estimate the viability of bacteria subjected to ozone treatment. An exposure to ozone (0.1 mg/l) for 16 min resulted in a 4.6 log cycle reduction of B. cereus and 7.7 log cycle reduction of S. Typhimurium. Among two bacteria studied, kmax (maximum death rate specific inactivation) was significantly higher for S. Typhimurium. The time required to obtain 4-log reduction (4-D value) was significantly (p<0.05) higher in B. cereus. The R2 values of 0.95 and above show that biphasic shoulder model was a good fit for the experimental data analyzed. The double Weibull parameters values were not significantly different for both bacteria studied. However, the 4-D values were significantly (p<0.05) higher for B. cereus as compared to S. Typhimurium. Estimated parameters also indicated the higher sensitivity of S. Typhimurium to ozone than B. cereus. The R2 values of 0.95 showed that the double Weibull model was also a good fit for the experimental data analyzed. The maximum difference between spectra of different samples was observed in the wavelength range of 230-320 nm. In general the optical density of bacterial culture treated with ozone decreased with increase in treatment time. The score plot following Principal Component Analysis (PCA) for both the bacteria treated with ozone for different time interval showed discrete grouping based on the time of treatment. The highest correct classification results for Soft Independent Modeling for Class Analogy (SIMCA) were achieved without any transformation of spectral data in the range of 230-320 nm for Bacillus cereus. However, in case of S. Typhimurium correct classification was obtained at higher time of exposure with ozone (i.e. 8 or 16 minutes). The partial least squares regression (PLSR) was used for prediction and quantification purposes. Maximum R2 values for calibration and validation were found to be 0.84 and 0.80, respectively, in the range of 230-320 nm using PLS for B. cereus. The R2 values for calibration and validation in case of S. Typhimurium was found to be 0.90 and 0.89 respectively.