The effects of different concentrations of natamycin and the point of addition on some physicochemical and microbial properties of vanilla-flavoured yoghurt under refrigerated condition

Yogurt is among the most common dairy products consumed around the world. Although it has many desirable properties, the product is still susceptible to deterioration during refrigeration. The study was carried out to determine the effects of different concentrations of natamycin and the point of its addition on some physicochemical properties of vanilla-flavoured yoghurt stored under refrigeration at 5 ± 1°C. Yoghurt samples were preserved by addition of Natamycin at concentrations of 5, 6, 7, 8, 9 and 10 ppm. Total soluble sugars and pH decreased while titratable acidity increased during the 28 days of storage. The changes in quality parameters were not as pronounced in samples containing 8, 9 and 10 ppm compared to those with lower concentrations of the preservative. The preservative effectively and significantly reduced yeast counts at these higher concentrations, while yeast levels increased in yoghurts with zero, 5 and 6 ppm. The concentration of 8 ppm resulted in the highest percentage decrease in yeast counts of yoghurt samples and was consequently used as the appropriate concentration of natamycin for preservation. Generally the addition of 8 ppm resulted in no significant differences (p 0.05) in the changes in four quality parameters of yoghurt analyzed.