Lactic, acetic, citric, and butyric acids were identified as the main organic acids in X2 and Y2. The changes in the amount of these organic acids during cold storage are presented in Figure 5. Lactic acid and citric acid were the most abundant acids in Y2 and X2 samples during cold storage. Unlike X2, a little amount of formic acid, which might be due to the growth of Bifidobacteria as stated by Seckin and Ozkilinc (2011), was also detected in Y2 during cold storage (data not shown). Formic acid was not significantly affected by the storage time (p > .05). It was probably due to the limited growth of Bifidobacteria during cold storage. Adhikari, Grün, Mustapha, and Fernando (2002) also indicated that the metabolic inertness of the bifid bacterial cells can occur when they were added to the yogurt after fermentation.