The IFpH did not affect the viscosity of T1 and T2. Also, the changes in viscosity values of T1 and T2 were similar during cold storage (Figure 4a,b). In T1 and T2, S. thermophilus was the sole fermenting organism. No symbiotic relationship exists during fermentation as L. delbrueckii subsp. bulgaricus is absent in the starter culture (Shihata & Shah, 2002). However, it was observed that the IFpH significantly affected the viscosity values of X1, X2, Y1, and Y2 (p < 0.05). Also, Y1 and Y2 had higher viscosity values than X1 and X2. The difference between YC‐X11 and ABY‐2 was maximum in the case of the IFpH of 4.80. The increment trend was also significantly different for X1, X2, Y1, and Y2 during cold storage (p < .05). Although pH changes in X1 and T1 were similar during cold storage, T1 had higher viscosity than X1 (p < .05). Shihata and Shah (2002) reported that proteolytic strains of L. delbrueckii subsp. bulgaricus are capable of hydrolyzing proteins and this may have led to reduction in viscosity of yogurt samples. In this study, it was similarly found that X1 and Y1 containing L. delbrueckii subsp. bulgaricus had lower viscosities than T1. Compared with the plain starter cultures and the probiotic ones, the viscosity of the buffalo milk yogurt sample increased as the fermentation time increased at the initial stage of cold storage (Figure 4a). The probiotic cultures prolonged the fermentation time increasing the viscosity of the buffalo milk yogurt samples when only at IFpH 4.80. Similar trend was not observed at the IFpH 4.55 (Figure 4b). Shihata and Shah (2002) correlated the increased firmness of the yogurt samples with incorporation of L. delbrueckii subsp. bulgaricus to ABT‐4 starter cultures. In our study, similar trend was observed at both IFpH 4.55 and 4.80 for the first day of the storage. The attachment of mucogenic strains to the protein matrix via the exopolysaccharide (the amount was not measured in this study) might be a reason for the improvement in viscosity. It was also indicated that faster exopolysaccharide production can be occurred when mixed cultures were used (Shihata & Shah, 2002).