The effect of increasing milk total solids to 4 levels (14%,18%,23% and 27%) on the growth of starter cultures and chemical properties of yoghurt was studied. All samples were analyzed for acidity and counts of starter bacteria during fermentation and for total solids, fat, protein and syneresis for final product. Sensory assessments were also conducted. Results showed that increasing of milk total solids from 14 to 27%, increased the time of lag phase for both of starter bacteria. The time of lag phase in acidity curve also increased with increasing milk total solids. The growth and activity of starter bacteria improved in the samples with higher amounts of total solids. Increasing milk total solids to 23% improved sensory acceptability and decreased syneresis significantly (α=5%).

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