Abstract
The objective of this study was to separately describe the fitting uncertainty and the variability of individual cell in bacterial survival kinetics during isothermal and non-isothermal thermal processing. The model describing bacterial survival behavior and its uncertainties and variabilities during non-isothermal inactivation was developed from survival kinetic data for Bacillus simplex spores under fifteen isothermal conditions. The fitting uncertainties in the parameters used in the primary Weibull model was described by using the bootstrap method. The variability of individual cells in thermotolerance and the true randomness in the number of dead cells were described by using the Markov chain Monte Carlo (MCMC) method. A second-order Monte Carlo (2DMC) model was developed by combining both the uncertainties and variabilities. The 2DMC model was compared with reduction behavior under three non-isothermal profiles for model validation. The bacterial death estimations were validated using experimentally observed surviving bacterial count data. The fitting uncertainties in the primary Weibull model parameters, the individual thermotolerance heterogeneity, and the true randomness of inactivated spore counts were successfully described under all the iso-thermal conditions. Furthermore, the 2DMC model successfully described the variances in the surviving bacterial counts during thermal inactivation for all three non-isothermal profiles. As a template for risk-based process designs, the proposed 2DMC simulation approach, which considers both uncertainty and variability, can facilitate the selection of appropriate thermal processing conditions ensuring both food safety and quality.
Highlights
Thermal inactivation is the most often used procedure for controlling microbial contamination in processed foods, thermal processing at higher temperatures or longer heating times can induce chemical and physical deterioration in foods (Awuah et al, 2007; Fellows, 2009; Ling et al, 2015)
The frozen pure bacterial cultures were transferred to tryptic soy agar (TSA; Merck, Darmstadt, Germany) plate and incubated at 37◦C for 5 days, after which an isolated colony of each bacterium was transferred to 5 mL of tryptic soy broth (TSB; Merck, Darmstadt, Germany) in a sterile plastic tube, which was incubated at 37◦C for 24 h
If the problems described above can be overcome, it would be possible to model the heterogeneity of bacterial behavior throughout the entire manufacturing process
Summary
Thermal inactivation is the most often used procedure for controlling microbial contamination in processed foods, thermal processing at higher temperatures or longer heating times can induce chemical and physical deterioration in foods (Awuah et al, 2007; Fellows, 2009; Ling et al, 2015). The demand for food processing has begun to exceed the fundamental requirements of safety and shelf life, with more emphasis being placed on comprehensively labeled, high-quality, value-added foods that are convenient to consume (Awuah et al, 2007). In line with these goals, the microbial inactivation process in foods should be minimized. Many RTE foods, which maintain their quality through relieved long-time thermal inactivation higher than 80◦C but below 100◦C and storage at refrigeration temperatures, have been introduced These products are called long-life refrigeration foods. The control of spore-forming bacteria can help ensure food safety and quality of minimally processed RTE foods preserved at refrigeration temperatures
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