Optimization of fruit yoghurt formulation and quality evaluation during storage

In this study, the effect of "Osmodehydrofrozen" fruits on sensory, physical, chemical and microbiological properties of yoghurt and its quality during storage was evaluated. The experiment conducted in two stages. At the first stage, the fruit percentage, type and addition time (before and after of fermentation) was determined, the results indicated that yoghurts which contained 10% apple or 13% strawberry which was added after fermentation had better quality. Because of high osmotic activity of apple, the synersis value was lower in apple yoghurt. According to osmotic activity in both fruits, the synersis value was very lower than fruit yoghurts which contained untreated fruits. Taste value was higher in strawberry yoghurt and texture and mouth feel values were higher in the yoghurt with high percentages of fruit. The results of second stage (quality evaluation during storage) indicated that storage had significant effect on pH, acidity, synersis, taste and texture (p<0.05). No mold and yeast grew in samples containing apple and Coli forms disappeared after 7 days of storage. In samples which contained strawberry, yeasts grew and coli forms disappeared after 7 days of storage.