Inhibition of nutrient- and high pressure-induced germination of Bacillus cereus spores by plant essential oils

• Essential oils showed variable antibacterial activity against B. cereus vegetative cells and spores.
• Most essential oils inhibited nutrient and high pressure (HP)-induced germination.
• Carrot seed essential oil had antibacterial activity but did not inhibit germination.
• Inhibition of HP germination by essential oils may adversely affect HP spore inactivation.

The efficiency of high-pressure (HP) treatment to eliminate vegetative bacterial cells is synergistically increased by many natural antimicrobials, but the effects on spores are poorly described. Here we report the effect of eleven plant essential oils on the nutrient- and HP-induced germination of spores of a group VI psychrotolerant Bacillus cereus strain. Ten oils partially inhibited nutrient-induced germination. These oils also inhibited HP-induced germination, but some inhibited only germination at moderate (200 MPa) pressure and others only at very high (600 MPa) pressure. Inhibition of spore germination by essential oils may have an adverse effect on the effectiveness of spore inactivation by HP at moderate temperatures, and this should be taken into account when designing combined processes. Essential oil from carrot seed did not inhibit nutrient or HP germination although it showed growth inhibitory properties, and essential oils with these properties may therefore open interesting perspectives in combination treatments with HP.Industrial relevanceHP treatment is an alternative processing technique that preserves a better balance of food quality and microbiological safety as compared to thermal processing. While most vegetative bacteria are efficiently inactivated by HP, inactivation of spores is inefficient. At moderate temperature, spore inactivation proceeds in a two-step process in which spores first germinate and are subsequently inactivated. The combination with natural antimicrobials is a promising approach to enhance the efficiency of HP processing because it exerts a synergistic effect on inactivation of vegetative bacteria. However, the current work is one of the first to document the effect of essential oils on the HP-induced germination of spores.