Abstract
Ultra high pressure homogenization (UHPH) opens up new areas for dynamic high pressure assisted thermal sterilization of liquids. Bacillus amyloliquefaciens spores are resistant to high isostatic pressure and temperature and were suggested as potential surrogate for high pressure thermal sterilization validation. B. amyloliquefaciens spores suspended in PBS buffer (0.01 M, pH 7.0), low fat milk (1.5%, pH 6.7), and whole milk (3.5%, pH 6.7) at initial concentration of ~106 CFU/mL were subjected to UHPH treatments at 200, 300, and 350 MPa with an inlet temperature at ~80°C. Thermal inactivation kinetics of B. amyloliquefaciens spores in PBS and milk were assessed with thin wall glass capillaries and modeled using first-order and Weibull models. The residence time during UHPH treatments was estimated to determine the contribution of temperature to spore inactivation by UHPH. No sublethal injury was detected after UHPH treatments using sodium chloride as selective component in the nutrient agar medium. The inactivation profiles of spores in PBS buffer and milk were compared and fat provided no clear protective effect for spores against treatments. Treatment at 200 MPa with valve temperatures lower than 125°C caused no reduction of spores. A reduction of 3.5 log10CFU/mL of B. amyloliquefaciens spores was achieved by treatment at 350 MPa with a valve temperature higher than 150°C. The modeled thermal inactivation and observed inactivation during UHPH treatments suggest that temperature could be the main lethal effect driving inactivation.
Highlights
Bacterial spores pose a major hazard in food safety because of their high resistance to most hurdles
The adjusted R2 was determined to evaluate the accuracy of fitting models and showed that the use of a nonlinear model to describe B. amyloliquefaciens spore thermal inactivation is more appropriate from a statistical point of view
Impact of the Homogenization Pressure on B. amyloliquefaciens Spore Inactivation Based on Figure 4, it could be tempting to conclude that there is a linear correlation between homogenization pressure and inactivation
Summary
Bacterial spores pose a major hazard in food safety because of their high resistance to most hurdles. Thermal sterilization is an effective method to inactivate bacterial spores, it has negative effects on sensorial and nutritional qualities of foods (Reineke et al, 2013; Georget et al, 2014b). Alternative preservation technologies have been investigated to inactivate bacterial spores while retaining sensorial and nutritional properties, such as high isostatic pressure (Mathys et al, 2007a; Reineke et al, 2011a, 2013; Georget et al, 2015), pulsed electric fields (Siemer et al, 2014a,b; Toepfl et al, 2014), ultra-violet light (Baysal et al, 2013; Gayán et al, 2013), and ultrahigh pressure homogenization (UHPH) (Georget et al, 2014a,b). The products are of improved sensorial and nutritional characteristics, among others, because of the increased emulsion stability and very short residence time at high pressure and/or high temperature (Zamora and Guamis, 2015)
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