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

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 500 mg L−1 dextrose and 3 mg L−1 MnSO4·H2O, incubated at 50 °C for 7 d. Spores were suspended (1.7 × 108 CFU mL−1) in tomato juice (pH 4.23) and treated at 600 MPa and process temperatures of 75, 85, 95, 100 and 105 °C, or 0.1 MPa and process temperatures of 100 and 105 °C for ≤15 min. 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 30 s pressure come-up time. Pressure holding times of 10, 7, 4 and 3 min and 40 s were sufficient to inactivate the spores to below the detection limit (<10 CFU mL−1) at 600 MPa 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 4 min, 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 (600 MPa, 105 °C) to 2.10 min (600 MPa, 75 °C), while they were 1.66 and 0.59 min 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.

► Studied pressure-thermal inactivation of Bacillus coagulans spores in tomato juice. ► Spore inactivation kinetics was described using linear and non-linear models. ► Combined pressure-heat treatment can help preserve shelf-stable tomato juice.