Evaluating the Antimicrobial Effect of Eucalyptus globulus Oil on Yeast Kluyveromyces marxianus: A Study on Biopreservative in Heat Treated Noncarbonated Doogh

The purpose of this study was to investigate the application of natural preservatives as an alternative to chemical preservatives in the production of Doogh. In order to carry out the work, different concentrations (0.25, 0.5, 0.75, 1, 1.5, 3%) of Eucalyptus essential oil were employed to study the growth of Kluyveromyces marxianus in Doogh at 4 °C and 15°C within 9 days. The essential oil of the plant was prepared by the hydro-distillation method and the chemical analysis was carried out by the application of Gas Chromatography -Mass Spectroscopy (GC/MS). Minimum Inhibitory Concentration (MIC) for Eucalyptus oil was determined through an agar diffusion method. The inhibitory effect and sensory characteristics of the oil were measured during 9 days of storage at 4 and 25°C. Chemical analysis of the oil indicated the presence of 15 compounds where Eucalyptol was the major constituent (78.68%) followed by γ - Terpinene (7.02%), α- Pinene (4.16%) and α- Terpinene (1.69%). The results showed that the number of K. marxianus in Doogh during storage time depended on the concentration of the used essential oil in the samples and storage temperature. It therefore might be concluded that the application of Eucalyptus essential oil to samples stored at 4°C and 25°C as a natural preservative might improve the desirable microbial, chemical and sensory properties of Doogh.