Thermal death time kinetics of three Bacillus strain probiotics in peptone media

The need for healthy foods has only increased in current years. Probiotics in particular are well known for their ability to provide a health benefit for the gut. The main probiotic bacteria commonly used in foods, Lactobacillus and Bifidobacterium, are susceptible to heat and therefore the products to which they can be added are limited. Spores of Bacillus strain bacteria were proposed as an alternative to Lactobacillus due to their thermal resistance. This research studied the thermal death time kinetics of three Generally Recognized as Safe (GRAS) Bacillus probiotic strains: Bacillus coagulans GBI-30 6086, Bacillus coagulans MTCC 5856, and Bacillus subtilis DE111. Firstly, the thermal resistance of each strain was evaluated at 83℃+/-3℃ and 100℃+/-3℃. This internal temperature was achieved through the use of an oil bath. A buffered peptone solution was allowed to come to temperature (5min+/-10sec) before the timer was started. A sample of the probiotic containing solution was then removed every 5min over the course of 20 minutes (time points: 0, 5, 10, 15, 20). The data were then analyzed to find the thermal resistance and the decimal reduction time (D-value). The D-value is the time it takes to attain a 1 log reduction in the microbial population. The D-values were then used to calculate the Z-value, which is the degree of temperature change needed to reduce the D-value by 1 log. All experiments had four independent replications. It was found that at 83℃ DE111 had the highest thermal resistance (D-83℃ 26min) while GBI-30 6086 had the lowest (D-83℃ 6min 48sec). The D-83℃ value for MTCC 5856 was not determined as this is an activation time and temperature for the strain. At 100℃ the D-100℃ for GBI-30 6086 was 3min 6sec, for DE111 was 2min 24sec, and for MTCC 5856 was 1min 12sec. This indicates that at 100℃ GBI-30 6086 has the highest thermal resistance and MTCC 5856 has the lowest.