Evaluation of whey powder on starter cultures activity, physico-chemical and sensory properties of yoghurt

In the current study, the percentages of 0, 0.25, 0.5, 0.75, 1, 1.25, 1.75 and 2% whey powder were used for yoghurt production. The physicochemical, sensory and microbial properties of samples were analyzed at 1 and 14 day of storage at 4°C. Chemical analysis showed that the higher whey powder decreased protein, pH and moisture content, while the amount of ash, acidity and reducing sugar increased. Based on the results of sensory evaluation, the highest sensory scores were obtained by replacing 0.5 and 0.75% whey powder (samples 2 and 3). This ratio can be used to reduce production costs. In addition, the microbial analysis illustrated that the samples were prepared from higher ratios of whey powder, the counts of S. thermophilus and L. delbrueckii were higher than the other samples.