Inhibition of Spoilage Yeasts using Spice Essential Oils and Their Components

Clove bud, cinnamon bark, and thyme oil, along with their components cinnamaldehyde, cinnamic acid, eugenol, carvacrol, and thymol, are widely acknowledged to have antimicrobial properties against bacteria. However, less is know about the inhibitory properties of essential oil components against spoilage yeasts. In this study a minimum inhibitory concentration (MIC) for these essential oils and components was determined using an agar dilution assay for Torulaspora delbrueckii, Candida krusei, Schizosaccharomyces pombe and Zygosaccharomyces bailii. The efficacy of essential oil components eugenol, carvacrol, cinnamaldehyde and thymol then were evaluated in a model salad dressing. The MIC against all yeasts for cinnamaldehyde and cinnamon bark oil was 50 mg/l. For thymol, thyme oil and carvacrol, the MICs were 200, 400, and 200 mg/l, respectively. T. delbrueckii and C. krusei required 300 mg/l to achieve an MIC for clove bud oil, and S. pombe and Z. bailii had an MIC of 200 mg/l. Eugenol had a MIC of 300 mg/l for T. delbrueckii, and C. krusei and an MIC of 200 mg/l for Z. bailii and S. pombe. Cinnamic acid had an MIC of 500 mg/l for Candida krusei and T. delbrueckii, 400 mg/l for S. pombe, and 200 mg/l for Z. bailii. To establish efficacy of essential oil components in salad dressing, 4 log CFU/m of yeast cells were added to 39.0±0.5g of model salad dressing with various concentrations of essential oils and incubated at 22˚C. Samples were taken at 0, 6, 12, 24, 48, 72, 96 and 120 h. Cinnamaldehyde at a 500 mg/l concentration was the most effective at inhibiting S. pombe and Z. bailii. T. delbrueckii and C. krusei used in this study were unable to grow in the model salad dressing used during the timeframe of the study.