evaluation of physicochemical changes and survival of probiotic bacteria in synbiotic yoghurt

abstract: yoghurt is a popular healthy food, consumed by many people. the popularity of this product made it possible to use it as a base in order to produce probiotic preparations. prebiotics are used for better growth and survival of probiotic bacteria as well as to improve organoleptic, rheological and technological properties of probiotic yoghurt. the aim of this research was to study physicochemical changes and survival of probiotic bacteria in synbiotic yoghurt. in this study, prebiotics including lactulose, inulin and oligofructose were used separately and probiotic bacterium lactobacillus casei was used to prepare the yoghurt. samples were stored at 4°c for 21 days and during this time ph, acidity, syneresis and probiotic counts were investigated and compared to the control (probiotic yoghurt without prebiotics). the results showed that the highest ph, the most probiotic counts and the highest taste and texture scores were related to the sample which had inulin. in contrast the control sample had the least probiotic count and the lowest score concerned with taste and texture. this sample had the least percent of syneresis which wasnt significantly different from others. the most and the least acidity were related to the control sample and the yoghurt containing lactulose, respectively. the results suggested positive effect of synbiotic in probiotic yoghurt. based on this study, since prebiotics improve physicochemical properties and enhance probiotic bacteria survival they can be incorporated in yoghurt formulation.  the results show that inulin has a better effect on physicochemical changes and probiotic bacteria survival as compared to other prebiotics.   keywords: inulin, lactobacillus casei, lactulose, oligofructose, synbiotic yoghurt.