Over past years, a dairy product called probiotic yogurt has been manufactured known as a functional food. In order to increase activity and improve growth and survival of probiotics and to improve technological properties of probiotic yogurt, prebiotics are added to its formulation. The aim of this study was to evaluate the effect of prebiotics (lactulose and inulin individually, and as mixture) on physicochemical properties and survival of Lactobacillus casei in synbiotic yogurt. The samples were examined for pH value, acidity, syneresis and probiotic bactria counts on 1,7,14 and 21 days of cold storage and then were compared to the control sample (probiotic yogurt without prebiotics).The results showed that the highest and the lowest pH value measured in the samples containing lactulose and lactulose-inulin, respectively. The control sample and the sample containing lactuloseinulin mixture showed the highest and the lowest acidity, respectively. Control sample and the sample containing lactulose-inulin showed the highest and the lowest syneresis on 1 d, respectively. At the end of storage period, yogurt containing lactulose-inulin showed the lowest syneresis, having a significant difference (p<0.05) as compared with other samples. Viability of probiotic bacteria showed an ascending trend by the end of second week, but it declined from 14 d to 21 d. The highest and the lowest probiotic bacteria counts observed in the sample containing lactulose-inulin and the control sample, respectively.
