Assessment the Quality of Probiotic Yogurt with Rosmarinus Officinalis Essential Oil

Introduction: The antimicrobial compounds have attracted attention these days all around the world. Applying essential oils (EOs) as the herbal antimicrobial materials and natural antioxidant are so valuable in the food industry. In this study the effects of Rosmarinus officinalis essential oil (REO) with different phenol contents was investigated on the properties of probiotic yogurt containing Bifidobacterium bifidum. Methods: The yogurt was prepared by adding the Lactobacillus bulgaricus and Streptococcus thermophiles as the starter and the Bifidobacterium bifidum as probiotic strains. The REO was added at 3 levels of 1%, 2% and 3%. The titratable acidity, pH, syneresis, rheological, microbial and sensory properties were evaluated at three storage time points (7, 14 and 21 days). The total phenol content was about 8.93 ± 0.11 mg gallic acid. Results: The bacterial activity significantly declined in all samples during 20 the storage (p < 0.05). Adding REO caused decreasing in the lowering rate of bacterial growth for both probiotic and starter strains over 21 days. Refrigerated storage decreased pH and viscosity (p < 0.05) but increased titratable acidity (TA) and syneresis (p < 0.05). The probiotic yogurt with REOs showed thixotropic non-Newtonian behavior. The samples containing 1% REO had the highest score of flavor, odor, texture, and overall acceptability. Conclusion: In conclusion, the high level of phenolics positively contributed to the biological, physicochemical and rheological properties of probiotic yogurt, as well as the sensory scores.