Effect of thymol in heating and recovery media on the isothermal and non-isothermal heat resistance of Bacillus spores

• Thymol in the heating medium has low influence on Bacillus spores heat resistance.
• Thymol in the recovery medium reduces Bacillus spores heat resistance.
• The dose-dependent effect of thymol in the recovery medium can be modelled.

Members of the genus Bacillus include important food-borne pathogen and spoilage microorganisms for food industry. Essential oils are natural products extracted from herbs and spices, which can be used as natural preservatives in many foods because of their antibacterial, antifungal, antioxidant and anti-carcinogenic properties. The aim of this research was to explore the effect of the addition of different concentrations of thymol to the heating and recovery media on the thermal resistance of spores of Bacillus cereus, Bacillus licheniformis and Bacillus subtilis at different temperatures. While the heat resistance was hardly reduced when thymol was present in the heating medium, the effect in the recovery medium was greater, reducing the D100 °C values down to one third for B. subtilis and B. cereus when 0.5 mM thymol was added. This effect was dose dependent and was also observed at other heating temperatures.