ABSTRACT
Aims: The objective of this study is to use different essential oils (cinnamon, clove, rosemary, almond sweet, sesame, wheat germ, and cedar wood) in concentrated yoghurt as antimicrobial agents to increase shelf life of concentrated yoghurt. Place and Duration of Study: Department of Food Technology, Faculty of Science and Technology, Al-Quds University, Palestine, between January 2015 to August 2016. Methodology: Essential oils were added to concentrated yogurt at a concentration of 250 μl\kg. Antibacterial activity and properties of major borne bacteria such as total aerobic count bacteria, yeast, mold, Staphylococcus aureus, were evaluated by plate count method, (pouring plate method). All yogurt samples were sensory evaluated for flavor, body and texture, and appearance. Total solid content, and titratable acidity of different yogurt samples were also determined. Results: Total solids and pH of concentrated yogurt samples treated with essential oils were only slightly affected. The best three essential oils used in terms of influence on total bacterial viable count and mold count were found to be cinnamon, clove and rosemary. The most acceptable organoleptic properties of treated concentrated yogurt were those samples treated with sesame and rosemary oils. Conclusion: The addition of cinnamon, clove and rosemary essential oils could increase the shelf life of concentrated yogurt.