Effect of Sesame oil and Homogenization Pressure on the Physicochemical, Qualitative and Microbial Characteristics of Yogurt

Yogurt is one of the widespread dairy products, which is especially important in people's diets due to its high nutritional value and health-promoting effect. In this study, the physicochemical, quality, sensory, and microbial characteristics of yogurt containing sesame oil (1, 2, and 3%) after homogenization at two pressures of 100 and 200 bar, for 21 days storage was investigated. The samples with sesame oil had higher pH and this value increased with increasing homogenization pressure. During storage, acidity of all yogurt samples increased. Moreover, peroxide value of yogurt increased and this value was higher in sesame oil samples. Syneresis was higher in yogurts with sesame oil, but this value decreased with increasing oil especially in yogurt containing milk fat. Power law was fitted appropriately by experimental data of rheological properties. Sesame oil addition resulted in no significant effect in hardness value of samples in comparison with milk fat. The lightness of yogurts showed that only the sample contained 3% sesame oil and treated at 100 bar pressures had significant difference with other samples (P<0.05). Microbial characteristics of samples were in accordance with institute of standards of Iran. Although, sensory evaluation of samples showed that yogurt containing sesame oil had better texture than yogurt containing milk fat; however, taste and mouthfeel of them showed lower scores. Sesame oil addition caused reducing overall acceptability of yogurts that may be related to the applying of oil without deodorization.