Kinetics of Bacillus coagulans spore inactivation in tomato juice by combined pressure–heat treatment

Abstract

The efficacy of combined pressure–heat treatment was evaluated for the inactivation of Bacillus coagulans spores in tomato juice. A spore crop of B. coagulans 185A was prepared on nutrient agar plus 500mgL−1 dextrose and 3mgL−1 MnSO4·H2O, incubated at 50°C for 7d. Spores were suspended (1.7×108CFUmL−1) in tomato juice (pH 4.23) and treated at 600MPa and process temperatures of 75, 85, 95, 100 and 105°C, or 0.1MPa and process temperatures of 100 and 105°C for ≤15min. The inactivation data was fitted to estimate kinetic inactivation parameters using selected linear and non-linear models. The models were evaluated using the mean square error, regression coefficient and accuracy factor. Depending upon the process temperature, a combined pressure–heat treatment reduced the spore population by 1.5–3.4 logs during the 30s pressure come-up time. Pressure holding times of 10, 7, 4 and 3min and 40s were sufficient to inactivate the spores to below the detection limit (<10CFUmL−1) at 600MPa and 75, 85, 95, 100 and 105°C, respectively with no microbial growth during subsequent storage of samples at 37°C. In contrast, the application of heat alone needed holding times of 13 and 4min, at 100 and 105°C, respectively to inactivate the spores to undetectable level with no growth during storage. The D-values of spores inactivated by combined pressure–heat treatment ranged from 0.19 (600MPa, 105°C) to 2.10min (600MPa, 75°C), while they were 1.66 and 0.59min at 100 and 105°C, respectively under atmospheric conditions. Kinetic model analysis indicated relatively good fits of linear and Weibull models to the pressure–heat inactivation data at process temperatures of 75–95°C. The log-logistic model provided best fitting at process temperatures of 95–105°C. This study suggests that combined pressure–heat treatment may be used as a viable alternative to inactivate B. coagulans spores in acidic food products, like tomato juice.