The effect of partially-replacing skim milk powder with whey powder in set-type yogurt manufacture

In this study, set-type of yogurts were produced with 7 different combinations of whey (WP) powder and skim-milk powder (SMP). The yogurts were analyzed for total solids, fat, non-fat solids, protein and ash contents on the first day of production while viscosity, syneresis, pH, volatile fatty acids, acetaldehyde and tyrosine values, and sensory evaluation were performed on days 1, 7 and 14 of storage. The effect of the fortification levels of whey powder on the viscosity value, syneresis rate, volatile fatty acids and tyrosine contents of trial yogurts were found to be significant (P<0.01). In contrary, pH value and acetaldehyde contents were not significantly changed. It was observed that the viscosity value, volatile fatty acids and tyrosine contents of yogurt samples increased (p<0.01) while syneresis rate, pH value and acetaldehyde content decreased (P <0.01) during storage. Sensorial evaluations showed that the addition of whey powder until the level of 1.0% (sample C) was more acceptable than control (sample A).