Encapsulation of Zataria multiflora Essential Oil in Saccharomyces cerevisiae: Sensory Evaluation and Antibacterial Activity in Commercial Soup

Nowadays rising consumer concern on the safety of synthetic chemical food preservatives is a reason for finding natural new antimicrobial agents, especially among the components of medicinal plants such as Essential Oils (EOs). However, most EOs are sensitive to oxygen, light, and temperature and can be easily degraded. Some EOs have strong taste, flavor, and affect the organoleptic characteristics of foods. Encapsulation can control these unpleasant characteristics. Using yeast cells as encapsulating agents and delivery systems for active ingredients has been widely investigated. Encapsulation in yeast cells has a wide range of advantages such as processes simplicity, commercial availability, low cost-high volume process, and needless of toxic solvents.  In this study, the antibacterial activity of free and encapsulated Zataria multiflora Bioss. Essential Oil (ZEO) in Saccharomyces cerevisiae against Escherichia coli O157:H7 and Listeria monocytogenes as important foodborne pathogens were evaluated. The sensory evaluation of both forms of ZEO in a food model was also done. ZEO was successfully encapsulated into S. cerevisiae cells. Carvacrol and thymol contents in loaded yeasts were determined. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of free and loaded ZEO were studied against Escherichia coli O157:H7 and Listeria monocytogenes; their antibacterial effects in the commercial chicken soup was investigated, and their sensory attributes in the commercial soup were evaluated as well. Our results showed significant decreases in the MIC and MBC values of ZEO in culture media after encapsulation; however, the antibacterial activity of ZEO in commercial chicken soup showed no significant differences after encapsulation (P>0.05). ZEO encapsulation improves its sensory score and hence, decreases its organoleptic effects in food (P<0.01). Considering acceptable sensorial scores of loaded ZEO in yeast cells, this method can practically be applied in food systems as natural biopreservation.