Unveiling the matrix effect on Bacillus licheniformis and Bacillus subtilis spores heat inactivation between plant-based milk alternatives, bovine milk and culture medium

This study examined the inactivation of spores of Bacillus licheniformis and Bacillus subtilis in four pea-based milk alternatives, semi-skimmed bovine milk and Brain Heart Infusion (BHI) broth to assess the matrix impact on the thermal inactivation of bacterial spores. Heat inactivation was performed with the method of capillary tubes in temperature range 97 - 110 degrees C. A four-parameter non-linear model, including initial level, shoulder duration, inactivation rate and tailing, was fitted to the data obtained. D-values were estimated and secondary Z T-value models were developed for both species. A secondary model for the shoulder length of B. licheniformis in a plantbased milk alternative formulation was built too. Models were validated at a higher temperature, 113.5 degrees C. Dvalues in the different matrices ranged between 2.3 and 8.2 min at 97 degrees C and 0.1 - 0.3 min at 110 degrees C for B. licheniformis. D-values for B. subtilis ranged between 3.9 and 6.3 min at 97 degrees C and 0.2 - 0.3 min at 110 degrees C. Z T- values in the different matrices ranged between 7.3 and 8.9 degrees C and 8.9 - 10.0 degrees C for B. licheniformis and B. subtilis, respectively. Significant differences in inactivation parameters were found within the pea-based formulations as well as when compared to bovine milk. Heat resistance was higher in pea-based matrices. Shoulders observed were temperature- and matrix-dependent, while no such trend was found for the tailings. These results provide insights, useful on designing safe thermal processing, limiting spoilage in plant-based milk alternatives and thus, reducing global food waste.