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

The effects of ethanol-soluble fractions of 12 plant extracts were tested for heat-sensitizing effects on the spores of Clostridium botulinum (type A and type B) and Clostridium sporogenes PA 3679. Licorice, pineapple sage and lemon eucalyptus extracts were respectively found to significantly decrease (P < 0.05) the thermal resistance of C. botulinum 62A (type A), C. botulinum Okra (type B), and C. sporogenes; reducing initial spore populations at 0.5–1.0% level of addition. Further investigations showed that increasing acidity and licorice extract (0.5%) had an additive heat- sensitizing effect on C. botulinum 62A while increasing NaCl counteracted the effect of the extract on the spores. Exposure of spores to 0.5% licorice extract for 7 d prior to heating significantly reduced the heat resistance of the spores. Finally, a post-heating sporicidal property of licorice extract was also observed, resulting in significantly greater spore population reductions compared to that when licorice extract was removed by washing with Tween 80 prior to enumeration on growth medium. The use of naturally occurring compounds in plants as potential food additives may help address the consumer demands for products with highly acceptable sensory and nutritive qualities, and safety.