Purpose: The objective of this study was to determine whether thyme, cinnamon, and clove oils or cinnamic acid, cinnamaldehyde, carvacrol, eugenol, thymol or allyl-isothiocyanate were effective against the spoilage yeasts Torulaspora delbrueckii (TD), Schizosaccharomyces pombe (SP), Candida krusei (CK) or Zygosaccharomyces bailii (ZB).
Methods : Yeasts were isolated from spoiled commercial products. An agar dilution assay in yeast extract glucose agar was conducted to determine minimum inhibitory concentrations (MICs) of EOs and EO components. Yeasts were spot inoculated and plates incubated at 32°C for 7 days. MIC was the lowest concentration with no growth.
Results : Susceptibility of yeasts to cinnamaldehyde, cinnamon bark oil, thymol, thyme oil and carvacrol was similar with MICs of 50, 50, 200, 400 and 200 µg/ml, respectively, for all species. Clove bud oil and eugenol had an MIC of 300 µg/ml against TD and CK while the MIC for SP and ZB was 200 µg/ml. Cinnamic acid inhibited CK and TD at 500 µg/ml, SP at 400 µg/ml and ZB at 200 µg/ml. Allyl-isothiocyanate was inhibitory only at > 500 µg/ml for all organisms.
Significance: The first step in evaluating antimicrobials is to determine their effectiveness against the target microorganism. All yeast species tested were susceptible to most EOs and components at low concentrations. While application in foods will require much higher concentrations for complete control, the potential sensory compatibility of EOs for products such as salad dressings, makes them good candidates for application studies.