Effect of grape syrup addition on the survival of probiotic bacteria, physico-chemical and sensory properties of yoghurt

In this research, grape syrup was used as a flavoring agent in probiotic yoghurt and accordingly physicochemical, microbial and sensory properties of the yoghurt were investigated. The results showed that grape syrup addition (5, 10 and 15% w/w) increased yoghurt fermentation time, however, these samples had higher acidity than control during storage. Viscosity was equal at first in all samples, but the viscosity of the yoghurts containing 10% and 15% w/w grape syrup reduced compared to control yoghurt, during storage. Syneresis was affected by grape syrup addition, which yoghurt containing 15% w/w grape syrup had the least syneresis. The results of color analysis demonstrated that grape syrup addition darkened the color and the L* factor reduced while a* and b*factors increased by raising the grape syrup concentration. Mold, yeast and coliform count were less than 10 cfu/ml in all the samples. Grape syrup addition increased the number of probiotic bacteria at first and during storage, which yoghurt containing 15% w/w grape syrup had the most live probiotic bacteria after 14 days of storage. Sensory evaluation of the samples represented that there was no significant difference between the samples flavor score while, grape syrup addition darkend the color and reduced appearance score. As a result, it can be concluded that addition of grape syrup to probiotic yoghurt offers a new choice for consumers as flavored yoghurt with added nutritional value and acceptable flavor accompanied with stimulated probiotic survival.