USE OF EXTRACELLULAR BIOEMULSIFIER FROM STREPTOCOCCUS THERMOPHILUSSTRADIS IN PRODUCTIOT OF FROZEN YOGHURT AS A PROBIOTIC FOOD

Four bacterial strains of Streptococcus PhelmophIlus p were cultivated in milk permeate and in M17 broth with lactose or glucose added to select the best strain which can grow on milk permeate or on M17 to give the highest extracellular bloemulsifiers yield which was produced by S. thetmophIlus p. The best strain was Streptococcus thennophilus p whIdi gave the highest growth on milk permeate at 37°C for 24 h at pH 7. Butter oil-in-water emulsions were stabilized over a broad range of conditions, from pH 2 to 11, with up to 5% sodium chloride or sucrose in the aqueous phase. In the presence of a low concentration of various solutes, emulsions were stable to three cycles of freezing and thawing. The main objective of this study was to manufacture frozen yogurt using different ratios of extracellular bioemulsifiers, which was produced by S. thermophilusp. The results showed that using extracellular bioemulsifiers had slight effect on increasing the specific gravity and weight per gallon In the resultant frozen yogurt In addition, extracellular bioemulsifiers reduced the rate of melting. Generally, using of extracellular bioemulsifiers In the manufacture of frozen yogurt improved whipping quality of the rub< and gave smoother body and texture. The preferable concentration of bioemulsifier produced by S. thermophaus p was 0.2% which enhanced viscosity, freezing point and overrun, and the product was more acceptable to consumers.