The essential oils of clove, thyme, black pepper, pimenta, origanum, garlic, onion, and cinnamon were evaluated for their effect on germination, outgrowth, growth, and toxin production of C. botulinum strains in microbiological media. The oils of clove, thyme, origanum, and cinnamon were studied for their mechanism of inhibition of C. botulinum 67B. The most effective oil, in combination with sodium nitrite at different levels was further tested against the growth and toxin production of C. botulinum (mixed types) in a meat model system.

Among all the spice oils, origanum and pimenta were the most effective in inhibiting six strains of types A, B, and E of C. botulinum in prereduced PY medium. These oils at a concentration of 200 ppm completely inhibited C. botulinum growth. Garlic, onion and black pepper exhibited the lowest inhibitory activity towards the growth of C. botulinum strains. Strains of type A were more sensitive to the inhibitory action of the oils than those of types B and E.

The inhibition of germination of C. botulinum by the eight spice oils indicated that garlic oil was the most potent inhibitor. Oils of pimenta, and clove were the least effective in inhibiting germination. The inhibitory effect of the oils was shown to be reversible. The oils appeared to have no significant effect on the outgrowth of the germinated spores. Nevertheless, the oils were highly active in inhibiting vegetative growth (cell division). Black pepper, clove, cinnamon, and origanum were the strongest inhibitors of vegetative growth. Yet, the oils had no direct effect on toxin production. The delay in toxin production caused by the oils was attributed to the effect of the oils on growth rather than on toxin production. Origanum oil acted synergistically with sodium nitrite in inhibiting the growth. of C. botulinum in a microbiological medium. In vacuum-packaged comminuted pork, origanum oil at 400 ppm, in combination with 50-100 ppm of sodium nitrite, significantly delayed the growth and toxin production of C.botulinum (mixed types). The probability of growth and toxin production of C. botulinum (p) in the vacuum packaged comminuted pork was calculated with Hauschild 's formula. The results showed that sodium nitrite significantly lowered p values, whereas origanum oil had very low effect on p values.