The Assessment the Quality of Probiotic Yogurt Using the Rosmarinus Officinalis Essential Oil

Antimicrobial compounds have recently attracted the attention of researchers across the world. Essential oils (EOs) could be used as potent herbal antimicrobial materials and natural antioxidants in the food industry. The present study aimed to assess the effects of Rosmarinus officinalis essential oil (REO) with variable phenol contents on the properties of probiotic yogurt containing Bifidobacterium bifidum.  Yogurt was prepared by adding Lactobacillus bulgaricus and Streptococcus thermophilus as the starter and the Bifidobacterium bifidum as the probiotic strains. REO was also added at the three concentrations of 1%, 2%, and 3%. Titratable acidity, pH, syneresis, and rheological, microbial, and sensory properties were evaluated at three storage times (7, 14, and 21 days). The total phenol content was approximately 8.93±0.11 milligrams of gallic acid.  The bacterial activity significantly declined in all the samples during 20 days of storage (P<0.05), and the addition of REO decreased the lowering rate of bacterial growth in the probiotic and starter strains over 21 days. Moreover, refrigerated storage decreased the pH and viscosity (P<0.05), which increasing increased titratable acidity and syneresis (P<0.05). The probiotic yogurt with REO exhibited thixotropic non-Newtonian behavior, and the samples containing 1% REO had the highest scores of flavor, odor, texture, and overall acceptability.  According to the results, high levels of phenolic compounds contributed to the biological, physicochemical, and rheological properties of probiotic yogurt, as well as its sensory scores.