It was found that the concentrations of lactic acid, acetic acid, and butyric acid in Y2 were higher than those of X2. The effect of the SCT on lactic acid and acetic acid production was not significant (p > .05). However, a significant difference was observed in butyric acid concentration (p < .05). Similarly, Donkor, Henriksson, Vasiljevic, and Shah (2006) reported that lactic acid concentration in yogurts containing probiotic culture was higher than the control containing standard yogurt culture. They also stated that the differences in lactic acid concentration were not statistically significant (p > .05). In contrast to the concentrations of other acids, it can be stated that X2 has higher amount of citric acid than Y2 (Figure 5c). Adhikari et al. (2002) noted that the citric acid content of the yogurts containing probiotic strains was lower than that of the control containing standard starter cultures. They related this result to the higher utilization of citric acid by the starter cultures during fermentation in the presence of bifid bacteria. As expected, the concentrations of organic acids significantly increased in both Y2 and X2 samples during cold storage with an exception of butyric acid (p < .05). Similarly, Adhikari et al. (2002) reported that there was no significant effect of the storage period on the concentration of butyric acid in set and stirred types of cow milk yogurt (p > .05). The SCT significantly affected the production of lactic acid, acetic acid, and citric acid during cold storage (Figure 5). The increases in the amounts of all organic acids presented in Figure 5 were found to be linear for X2 during 20 days of cold storage. However, for Y2, the amounts of lactic acid, acetic acid, and citric acid increased more rapidly in the first 10 days of cold storage. Then, the rate of increase slowed down gradually and further slight increases were observed throughout the storage period.