Effect of grape juice on the rheological, physicochemical and microbial characteristics of kefir beverage

Kefir is a fermented beverage made from milk which is high in probiotic. In this study the effect of addition of grapes juice at levels of 0, 1, 2, 3 and 4 percent on the microbial, physicochemical, rheological and sensory characteristics of kefir beverages was studied. The results showed that microbial flora, acidity index, redness, yellowness and apparent viscosity increased and the lightness and the pH value decreased by increasing grape juice levels. In order to the rheological results, by increasing the shear rate, the viscosity of all samples fell and, all samples exhibited shear thinning behavior under steady shear. Also, the Power low model showed the best fit with Kefir beverage. Sensory scores decreased by increasing grape juice levels (3 and 4 %). In overall, based on impact on lactic acid bacteria, yeast activity, color and flavor which are influenced by lactic acid bacteria activity, 2% concentration of grapes juice can be considered as the best level of grape juice to produce kefir beverage.