C. botulinum inactivation kinetics implemented in a computational model of a high‐pressure sterilization process

Abstract

High-pressure, high-temperature (HPHT) processing is effective for microbial spore inactivation using mild preheating, followed by rapid volumetric compression heating and cooling on pressure release, enabling much shorter processing times than conventional thermal processing for many food products. A computational thermal fluid dynamic (CTFD) model has been developed to model all processing steps, including the vertical pressure vessel, an internal polymeric carrier, and food packages in an axis-symmetric geometry. Heat transfer and fluid dynamic equations were coupled to four selected kinetic models for the inactivation of C. botulinum; the traditional first-order kinetic model, the Weibull model, an nth-order model, and a combined discrete log-linear nth-order model. The models were solved to compare the resulting microbial inactivation distributions. The initial temperature of the system was set to 90 degrees C and pressure was selected at 600 MPa, holding for 220 s, with a target temperature of 121 degrees C. A representation of the extent of microbial inactivation throughout all processing steps was obtained for each microbial model. Comparison of the models showed that the conventional thermal processing kinetics (not accounting for pressure) required shorter holding times to achieve a 12D reduction of C. botulinum spores than the other models. The temperature distribution inside the vessel resulted in a more uniform inactivation distribution when using a Weibull or an nth-order kinetics model than when using log-linear kinetics. The CTFD platform could illustrate the inactivation extent and uniformity provided by the microbial models. The platform is expected to be useful to evaluate models fitted into new C. botulinum inactivation data at varying conditions of pressure and temperature, as an aid for regulatory filing of the technology as well as in process and equipment design.

High-Pressure Processing Technologies for the Pasteurization and Sterilization of Foods

“…Immediately available to commercialize PATP technology, is alternative (c) in Table 2, i.e., temperatures above 100°C to inactivate bacterial spores in a reasonably short time. The limitation of this alternative is the need for research on reaction kinetics in the pressure and temperature range required for this alternative, a severe limitation at this time (Ramírez and Torres 2009;Torres et al 2009b;Martínez Monteagudo et al 2011;Valdez-Fragoso et al 2010) when compared to the large availability of data on the inactivation of bacterial spores (Reddy et al 2003;Margosch et al 2004Margosch et al , 2006aRajan et al 2006;Ahn et al 2007a,b;Paredes-Sabja et al 2007;Naim et al 2008;Zhu et al 2008;Juliano et al 2009;Ratphitagsanti et al 2009). …”

The Thermo-Egg: A Combined Novel Engineering and Reverse Logic Approach for Determining Temperatures at High Pressure

“…The rapid heating and cooling in HPT processing offers the potential for producing high-quality shelf-stable products, including improved colour, flavour, and nutrient retention [1,6,11,15] compared to traditionally thermally processed products. Despite the fact that pressure is uniformly distributed throughout the pressure vessel in HPT processing, temperature is not [7,8]. The development of temperature gradients in HPT processing is a result of the differences in compression heating of the materials involved, i.e.…”

“…Such nonuniform transient temperature distributions are aggravated by any temperature mismatch of the incoming compression fluid (which may comprise up to about 20% of the vessel's volume). Various heat retention aids, including internal electrical heaters and polymeric insulating product baskets, have been proposed to counteract the cooling caused by the vessel walls, and the performance of some of these has been assessed [7][8][9]. However, the issue of temperature gradients in HPT processing is likely to remain, as it also remains in traditional thermal retort processes.…”

“…It is also known that slight temperature variations could have a significant effect on bacterial spore inactivation [7,8]. Therefore, before HPT technology can be commercially implemented, particularly for shelf-stable low-acid food applications, there is a need to demonstrate that the process can be reliably and accurately monitored in terms of the temperatures achieved during processing.…”

High Pressure Processing of Meat, Meat Products and Seafood

“…Pressure is the predominant process parameter for the inactivation kinetics of vegetative cells in high pressure pasteurization applications; therefore, non-uniformity of the process field is limited. However, studies on the inactivation of spores under high pressure-high temperature conditions showed that temperature becomes a determining variable [13,72,73,152]. For process optimization purposes, the detection of the point of the lowest and higher impact is necessary to verify the effects of the treatment on safety and quality features.…”