Fatemeh Davoodi - Graduate of the Department of Food Science and Technology, Research Sciences Branch, Islamic Azad University, Tehran, Iran
Seyed Ebrahim Hosseini - Associate Professor, Department of Food Science and Industry, Research Science Branch, Islamic Azad University, Tehran, Iran
Gholam Hasan Asadi - Associate Professor, Department of Food Science and Industry, Research Science Branch, Islamic Azad University, Tehran, Iran

Yogurt is one of the most popular dairy producs which is consumed widely all over the world. Considering it's high nutritional values and containing valuble bacterias , it's widely popular .However today it has been concluded that increasing fat consumption in nutrition regime brings about vulnerability to many diseases. So in this study different kinds of internal stabilizers including arabic gum, karaginan,carboxylic methil cellulus and also external stabilizers such as alginat sodium , corn starch , and karaginan with conentation of .'۵ percent of it's weight , - added to low fat milk yogurt - were tken into consideratin.And in the course of the experiment samples of low fat yogurt obtained , were evaluated in terms of their chemical and sensory properties and senses of color ,taste and odor. In this study, the samples were tested for ۲۱ days and once every seven days , for their hydration, firmness.,ph, acidity ,free fatty acid.and also sensory properties .Considering obtained results , effect differences among different internal and external stabilizers on the qualitative and sensory properties of low fat yogurt samples were significant ( p < ۰/۰۵) furthermore ,the results .. during the storage time period -۲۱ days -showed that amount of hydration..and tissue firmness, in samples of low fat yogurt had been rising and has reached it's highes level on ۲۱th day of storage..However results also showed.staibilising effects on the acidity level, ph,and amount of free fatty acids of yogurt were not significant ( p > ۰/۰۵ ) . The results of stabilizer s effect on sensory properties of low fat yogurt samples did not show to be significant. In general on the basis of fhysico chemical results obtained yogurt samle containig carboxy met cellulose(T ۵) was introduced as the best treatment.

Acidity, Stabilizers ,Carboxi mettil cellulose ,Yogurt firmness