HEAT SENSITIZATION OF BACILLUS SUBTILIS SPORES BY SELECTED SPICES

Abstract

Commercially sterile garlic, sage, black pepper, cinnamon and clove were investigated as heat sensitizing agents towards Bacillus subtilis spores. Heat treatment at 80°C for 10 min of all spice‐spore mixtures (0.9 g spice/0.1 g spores) in distilled water (9 mL) reduced initial counts (106/mL) by approximately 0.5–1.0 logarithms, with the exception of garlic which showed no effect. The clove‐spore mixture exhibited the greatest reduction in survivor counts. Dry spice‐spore mixtures conditioned for 24‐96 h in relative humidities (RH) from 64 to 98% and at temperatures from 25 to 35°C, prior to heat treatment, exhibited additional reduction in survivors. The clove‐spore mixture exhibited the greatest decrease in heat‐treated survivors (approximately 4 logarithms) after conditioning at 96% RH and 35°C for 96 h. Relative humidity conditioning of cinnamon‐spore mixtures, regardless of treatment regime, did not reduce the number of heat‐treated survivors. Increasing the temperature and/or RH of conditioning for the remaining spice‐spore mixtures generally increased heat sensitization. Aw‐equilibrated spice‐spore mixtures which were not heat‐treated (controls) showed no reductions in viability. Moisture sorption by the spices during conditioning only partially influenced their heat sensitizing effects.

Heat-sensitizing effects of plant extracts on Clostridium spp. spores

“…In the suspension containing 4% lemon eucalyptus extract, a log linear inactivation curve was observed where the population of the inoculated spores was reduced by >5 log cycles after 60 min of heating. Blank et al (1988) explained that the varying degrees of efficacies of different plant extract maybe due to the innate diversity in the chemical and physical properties. Such properties include the amounts of essential oil present in the extract, and solubility in the suspending medium.…”

“…Licorice extract was also found to have heatsensitizing activity against C. sporogenes, although the activity was only about half of that of lemon eucalyptus. The heat sensitization of Bacillus subtilis spores by spices including garlic, sage, black pepper, cinnamon and clove were previously investigated by Blank, Akomas, Henderson, and Zawitowski (1988) who postulated that sensitization of spores may result from a chemical inactivation that is enhanced by heating.…”

“…Therefore removal of the extract after heating by Tween 80 consequently eliminated the inhibitory activity of the extract, hence resulting in significantly less reduction. Since the majority of antimicrobial substances in plant extracts are composed of sparingly water soluble phenolic compounds (Jurd, King, Milhara, & Stanley, 1971), adsorption of the antimicrobial compounds onto the spores was deemed important in inducing inactivation (Blank et al, 1988).…”

Optimization and evaluation of heat-shock condition for spore enumeration being used in thermal-process verification: Differential responses of spores and vegetative cells of Clostridium sporogenes to heat shock

“…Meanwhile, heat-shock conditions for the enumeration of spores should be sufficient to inactivate vegetative cells of any strains of spore-forming bacteria, like Bacillus and Clostridium (16,21); otherwise it may cause major errors in the accuracy of spore counts. To test if C. sporogenes vegetative cells can survive under a heat-shock condition of 90 o C for 10 min, therefore, we exposed vegetative cells (2×10 5 CFU/mL) to the heat-shock condition and observed that more than 99.5% of the cells lost their viability (data not shown).…”