Inactivation of Bacillus coagulans Spores Subjected to Combinations of High-Pressure Processing and Nisin
In this study, the influence of pressure (300 to 700 MPa), mild heat (15°C to 75°C), and nisin concentration (0 to 200 IU mL-1) on the survival of Bacillus coagulans AS 1.2009 spores in milk buffer at different processing times (7.5 to 17.5 min) was investigated. Response surface methodology (RSM) was employed, and a quadratic equation for high-pressure processing (HPP) and nisin-induced inactivation was developed using RSM. By analyzing the response surface and the corresponding contour plots, as well as solving the quadratic equation, the experimental values were significantly in agreement with predicted values; the adjusted coefficient of determination (RAdj2) was 0.9588, and the level of significance was p < 0.0001. The optimum process parameters for a 6-log cycle reduction of B. coagulans AS 1.2009 spores were pressure of 550.0 MPa, temperature of 41°C, pressure-holding time of 12.2 min, and nisin concentration of 120 IU mL-1. The adequacy of the model equation for predicting the optimum response values was validated effectively for ten test points. Compared to conventional HPP techniques, the main process advantages of combined HPP-nisin treatment in milk buffer are reduced requirements for pressure, temperature, and use of a natural preservative (nisin), with a shorter treatment time.