Synergistic and Antagonistic Effects of Combined Subzero Temperature and High Pressure on Inactivation ofEscherichia coli

Abstract

The combined effects of subzero temperature and high pressure on the inactivation of Escherichia coli K12TG1 were investigated. Cells of this bacterial strain were exposed to high pressure (50 to 450 MPa, 10-min holding time) at two temperatures (؊20°C without freezing and 25°C) and three water activity levels (a w ) (0.850, 0.992, and ca. 1.000) achieved with the addition of glycerol. There was a synergistic interaction between subzero temperature and high pressure in their effects on microbial inactivation. Indeed, to achieve the same inactivation rate, the pressures required at ؊20°C (in the liquid state) were more than 100 MPa less than those required at 25°C, at pressures in the range of 100 to 300 MPa with an a w of 0.992. However, at pressures greater than 300 MPa, this trend was reversed, and subzero temperature counteracted the inactivation effect of pressure. When the amount of water in the bacterial suspension was increased, the synergistic effect was enhanced. Conversely, when the a w was decreased by the addition of solute to the bacterial suspension, the baroprotective effect of subzero temperature increased sharply. These results support the argument that water compression is involved in the antimicrobial effect of high pressure. From a thermodynamic point of view, the mechanical energy transferred to the cell during the pressure treatment can be characterized by the change in volume of the system. The amount of mechanical energy transferred to the cell system is strongly related to cell compressibility, which depends on the water quantity in the cytoplasm.Food processing under high hydrostatic pressure is an emerging technology that has stimulated considerable interest within the food industry over the past 15 years. There are currently some interesting commercial opportunities and research challenges in the high-pressure processing of foods (42). This processing technique allows the manufacture of innovative food products while preserving the texture, color, raw flavoring agents, and nutritional value of the food, which are all aspects valued by consumers (22,36). Furthermore, high-pressure treatments cause the denaturation of several enzymes that are responsible for quality deterioration, as well as the inactivation of pathogenic and spoilage microorganisms (15). However, to achieve high or complete microbial inactivation, high pressures and/or long treatment times are required, so that the cost of the process seriously limits its industrial applications. For this reason, it would be beneficial to optimize high-hydrostatic-pressure processes.Numerous studies have demonstrated the temperature dependence of the antimicrobial effects of high pressure (19,25,39). Moreover, the efficiency of high-pressure treatments is controlled by other process parameters such as the applied pressure and the kinetics of pressurization (31), as well as by the physicochemical properties of the medium being treated, such as pH (1, 18) and water activity (10,26,43). Precise control of these parameters is necessary to ...

Damage in Escherichia coli Cells Treated with a Combination of High Hydrostatic Pressure and Subzero Temperature

“…Indeed, precise pressure and temperature monitoring made it possible to identify possible liquid-toice I, -ice III, and -ice V phase transitions (23).…”

“…Combined high-pressure and subzero-temperature treatments were performed as described previously (23). Two cryostats loaded with 95% ethanol as the circulating fluid were used consecutively to lower the temperature of the HHP vessel.…”

“…A very precise control of pressure and temperature is required to detect freezing in the cell suspensions being treated and to ensure pressurization in the liquid state. Recent studies reported pressurization in the liquid state at subzero temperature of yeast Saccharomyces cerevisiae (29), of the gram-positive bacterium Lactobacillus plantarum (29), and of the gram-negative bacterium Escherichia coli (23).…”

The biochemical and microbiological characteristics of rumen fluid from cattle co-grazed with and without camels as compared to that from the foregut of camels

“…Only one OTU showed 100% similarity with the RDP database, which resulted from the 401 OTUs that were only present in cattle co-grazed with camels. This significant occurrence of individual OTUs between cattle grazed alone and cattle co-grazed with camels indicated that the co-grazing factor does affect the dynamics of rumen microbial populations in the same way as other factors, such as diet transition (Tajima et al 2000), temperature (Moussa et al 2006), and antimicrobial tolerance (Goel et al 2005;Nelson et al 1998).…”

“…To date, no research has looked into the effects of co-grazing with different species on foregut bacterial populations. This is because, the majority of studies of microbial populations affected by environmental factors have focused on temperature (Moussa et al 2006), antimicrobial tolerance (Goel et al 2005;Nelson et al 1998), and diet transition (Tajima et al 2000). …”