Effect of Essential Oils on Germination and Growth of Some Pathogenic and Spoilage Spore-Forming Bacteria.

The use of essential oils as a food preservative has increased due to their capacity to inhibit vegetative growth of some bacteria. However, only limited data are available on their effect on bacterial spores. The aim of the present study was to evaluate the effect of some essential oils on the growth and germination of three Bacillus species and Geobacillus stearothermophilus. Essential oils were chemically analyzed using gas chromatography and gas chromatography coupled to mass spectrometry. The minimal inhibitory and bactericidal concentrations of vegetative growth and spore germination were assessed using the macrodilution method. Germination inhibitory effect of treated spores with essential oils was evaluated on solid medium, while kinetic growth was followed using spectrophotometry in the presence of essential oils. Essential oil from Drypetes gossweileri mainly composed of benzyl isothiocyanate (86.7%) was the most potent, with minimal inhibitory concentrations ranging from 0.0048 to 0.0097 mg/mL on vegetative cells and 0.001 to 0.002 mg/mL on spore germination. Furthermore, essential oil from D. gossweileri reduced 50% of spore germination after treatment at 1.25 mg/mL, and its combination with other oils improved both bacteriostatic and bactericidal activities with additive or synergistic effects. Concerning the other essential oils, the minimal inhibitory concentration ranged from 5 to 0.63 mg/mL on vegetative growth and from 0.75 to 0.09 mg/mL on the germination of spores. Spectrophotometric evaluation showed an inhibitory effect of essential oils on both germination and outgrowth. From these results, it is concluded that some of the essential oils tested might be a valuable tool for bacteriological control in food industries. Therefore, further research regarding their use as food preservatives should be carried out.

Effect of Drypetes gossweileri essential oil and irradiation treatments on inhibition and sensitivity of bacterial spores.

This work assesses the effect of Drypetes gossweileri essential oil on germination of Bacillus spores inoculated in orange juice and milk. We also report the capacity of the essential oil at 0.25, 0.5 and 1 µg/mL to induce sensitivity of spores to some irradiation treatments. The concentrations of essential oil were chosen after sensory analysis. The results show that the essential oil inhibited spores germination with minimal inhibitory concentrations inhibiting spore germination (MICg) of 10 µg/mL in the orange juice. In milk, the spores appeared to be less sensitive with MICg varying from 20 to 40 µg/mL. The sensory analysis revealed 2.5 µg/mL as the acceptable concentration of essential oil in orange juice. The essential oil at 1 µg/mL induced the sensitivity of spore of three Bacillus to alpha radiation of 101.4 Gy. Ultraviolet-C and microwave treatments in the presence of essential oil in general led to higher inactivation of spores up to 100% in some cases.