Formulating Fruit Yoghurt by Concentrated Milk and Evaluating its Quality During Storage

In this study, the effect of “Osmodehydrofrozen” fruit addition on sensory, physical, chemical and microbiological properties of concentrated yoghurt and its quality during storage was evaluated. This research was done in two stages. At the first stage, fruit percentage, type and addition time (before and after fermentation) was determined. The results indicated yoghurts containing 10% apple or 13% strawberry, which was added before fermentation had a better quality. Because of high osmotic activity of apple, the synersis was lower in apple yoghurt in comparison with strawberry yoghurt. According to osmotic activity of both fruits, the synersis value was much lower than that of fruit yoghurts, which contained untreated fruits. Taste value was higher in strawberry yoghurt and texture and mouth feel values were higher at low percentages of fruit. The results of the second stage (quality evaluation during storage) indicated that storage had a significant effect on pH, acidity, synersis, taste and texture (P<0.05). In samples which contained apple, coli forms disappeared after 7 days of storage. In samples that contained strawberry, coli forms disappeared after 7 days of storage.