Proteolytic Activity and Some Properties of Stirred Fruit Yoghurt Made Using Some Fruits Containing Proteolytic Enzymes

Stirred yoghurts with different fruit homogenates (papaya, kiwi, pineapple and kaki and control (without additive) were prepared and stored up to 14 days at 5±1°C. Sugar and fruit homogenates were added at the rate of 5 and 10% w/w respectively. The results revealed that, significant differences were observed in proteolytic activity, acidity, protein and fibers contents among all treatments. Addition of fruit homogenates and sugar had significantly harmful effect on the viability of the two lactic acid bacteria strains. The effect was more obvious with using pineapple or kiwi than other fruits. Lb. delbrueckii ssp. bulgaricus was much more sensitive to the fruit addition than Str. thermophilus. All yoghurt samples, however, contained the recommended levels of (10 -10 cfu/g) lactic acid bacteria at the end of the refrigerated storage. Yeasts and 6 7 moulds count was higher in fruit stirred yoghurt compared with the control and increased significantly during storage at 5±1°C. The yoghurt containing pineapple or papaya ranked higher flavour scores than those of other fruits.