Effect of fat content of milk on the growth and metabolic activity of starter cultures and quality of concentrated yoghurt

Effect of fa contet of milk (2. 7%، 5%، 7% and 9%) on the growth and metabolic activity of starter cultures during fermentation of concentrated yoghurt (23% total solid)، was studied. Sensory assessment of yoghurt samples were also obtained. The characteristics that was measured during fermentation include: PH، acidity، count of starter bacteria (stereptococcus thermophilus and Lactobacillus bulgaricus)، and the characteristics that measured in final product were sensory properties. The experiments were done in three replications. Statistical evaluation showed that increase in fat content of milk، had no significant effect on PH but resulted decreasing of acidity of samples. Addition of fat content from 2. 7% upto 9% decreased acidity from 0. 97% to 0. 78%. with increasing in fat content from 2. 7% upto 9% count of stereptococcus thermophilus decreased from 391×106 cfu/ml to 279×106 cfu/ml where fat content had no significant effect on growth of Lactobacillus bulgaricus. Addition of fat content did not influenced the sensory acceptability of final product.