Pressure-Based Strategy for the Inactivation of Spores

Abstract

Since the first application of high hydrostatic pressure (HHP) for food preservation more than 100 years ago, a wealth of knowledge has been gained on molecular mechanisms underlying the HHP-mediated destruction of microorganisms. However, one observation made back then is still valid, i.e. that HHP alone is not sufficient for the complete inactivation of bacterial endospores. To achieve "commercial sterility" of low-acid foods, i.e. inactivation of spores capable of growing in a specific product under typical storage conditions, a combination of HHP with other hurdles is required (most effectively with heat (HPT)). Although HPT processes are not yet industrially applied, continuous technical progress and increasing consumer demand for minimally processed, additive-free food with long shelf life, makes HPT sterilization a promising alternative to thermal processing.In recent years, considerable progress has been made in understanding the response of spores of the model organism B. subtilis to HPT treatments and detailed insights into some basic mechanisms in Clostridium species shed new light on differences in the HPT-mediated inactivation of Bacillus and Clostridium spores. In this chapter, current knowledge on sporulation and germination processes, which presents the basis for understanding development and loss of the extreme resistance properties of spores, is summarized highlighting commonalities and differences between Bacillus and Clostridium species. In this context, the effect of HPT treatments on spores, inactivation mechanism and kinetics, the role of population heterogeneity, and influence factors on the results of inactivation studies are discussed.

Effects of High Pressure on Bacillus licheniformis Spore Germination and Inactivation

“…One such technology is high-pressure (HP) processing, which reduces the microbial load without compromising the fresh quality of the food. Conditions of HP in the range of 200 to 600 MPa combined with low to moderate heat are currently used in the food industry to inactivate vegetative microorganisms or to modulate enzymatic reactions in food, but they have not yet been implemented for elimination of spores due to their high-pressure resistance at ambient temperatures (24,25). To achieve HP inactivation of spores, it is generally accepted that spores must first germinate and that germinated spores are inactivated by subsequent heat or pressure exposure in a two-step process (26,27).…”

“…High-pressure thermal sterilization (HPTS) is a strategy that exploits the synergetic effect of vHP (Ͼ500 MPa) and elevated temperatures (Ͼ60°C) on spore inactivation (24,34). However, due to technical limitations, temperature inhomogeneity in industrialscale vessels, and difficulties predicting spore inactivation kinetics, this method is not yet applied commercially (24,25).…”

Continuous Versus Discontinuous Ultra‐High‐Pressure Systems for Food Sterilization with Focus on Ultra‐High‐Pressure Homogenization and High‐Pressure Thermal Sterilization: A Review

“…Under these conditions the main inactivation force is the temperature (Reineke et al., ; Sevenich et al., ). Recently, the differences in germination under pressure between Clostridium spores and Bacillus spores have been revealed, showing interesting insights (Figure ; Doona et al., ; Lenz & Vogel, ; Paredes‐Sabja, Setlow, & Sarker, ). In Bacillus spp ., DPA release triggers cortex lytic enzyme (CLE) activation; CLE action is not essential for DPA release, but it can accelerate it.…”

Molecular Responses to High Hydrostatic Pressure in Eukaryotes: Genetic Insights from Studies on Saccharomyces cerevisiae

“…Generally, microorganisms can survive at high hydrostatic pressures in the range of several dozen MPa; a pressure higher than 200 MPa is lethal to most microorganisms but not to spores of Clostridium species, which are resistant to pressures greater than 400 MPa. The non-thermal sterilization of food materials using ultra-high pressure has been studied previously [ 8 , 9 ]. The effects of high pressure depend on the magnitude, pressurizing periods, temperature, pH, oxygen availability, and nutrient composition, which are complex and difficult to interpret.…”