Abstract
In the present study soybean (Glycine max L.) was included in cow and camel milk during fermentation. The resulting soybean-yogurt was evaluated with respect to the changes of post-acidification, viable cell counts (VCC) of Lactobacillus spp. and Streptococcus thermophilus, total phenolic content (TPC) and antioxidant activity using 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) inhibition assay during 21 days of refrigerated storage. The presence of soybean in fresh cow- and camel-milk yogurts did not affect pH reduction compared to respective plain-yogurt. However, soybean–camel milk yogurt showed significant reduction in pH (4.05±0.06) compared to plain-yogurt 4.35±0.02 on day 7 of storage. Titratable acidity (TA) increased in soybean–cow milk yogurt (p<0.05) but not in soybean–camel milk yogurt as compared with respective plain-yogurt during period of storage. The presence of soybean in fresh yogurt showed increased (p<0.05) in Lactobacillus spp. VCC by 10% in cow milk-yogurt and 30% in camel milk-yogurt compared to respective plain-yogurts. On the other hand, VCC of S. thermophilus was higher (p<0.05) in the presence of soybean in cow milk yogurt than in camel milk yogurt. Soybean–camel milk yogurt had 2-folds higher TPC on day 0 and 7 (149.59±1.8 and 111.44±2.8μgGAE/ml respectively) than plain-camel milk yogurt (60.04±0.01 and 55.22±0.01μgGAE/ml respectively). The highest value of TPC in soybean–cow milk-yogurt was showed on day 21 of storage (43.17±1.2μgGAE/ml). The antioxidant activity increased (p<0.05) in the presence of soybean in both cow and camel milk yogurts compared to respective controls. The highest antioxidant activity was shown on day 0 for soybean–cow milk yogurt (61.76±2.2%) and day 7 for soybean–camel milk yogurt (53.16±0.1%). In conclusion, the addition of soybean in both cow- and camel-milk yogurts enhanced the viability of LAB and antioxidant activity during refrigerated storage.