This research investigated the quality properties of yogurts added to barley (1, 2, and 3%) and tagatose or sucrose. After inoculation of S. thermophilus, pH, titratable acidity (TA), viscosity, and viable cell count were measured at 4 h intervals for 16 h and color value, antioxidant activity, and sensory evaluation were determined after fermentation in triplicate. In the case of yogurt containing only tagatose or sucrose, the pH was hardly decreased, but when 2-3% barley was added, the pH reached below 4.5 before 16 h. In addition, TA and viscosity tended to increase as barely was added. Viable cell count increased slowly in yogurt with tagatose, but rapidly increased when barley was added. As barley content increased, yellowness, redness, and antioxidant activity tended to increase, and significantly higher antioxidant activity in barley tagatose yogurt. Sour strength increased and significant difference in the sweetness was not observed when barley amount increased. Although there was no significant difference in overall acceptability, tagatose yogurt containing 3% barley scored the highest in preference. In conclusion, the fermentation rate of yogurt inhibited by the addition of tagatose is improved by the addition of barley, and the growth rate of lactic acid bacteria is considered to play a role.

To investigate the effects of tagatose added to yogurt fermented with Streptococcus thermophiles (ST) or Lactobacillus delbrueckii subsp. Bulgaricus (LB), pH, titratable acidity (TA), sugar content, color value, viable cell number, and sensory evaluation were determined on yogurts added with 7% sucrose, tagatose, or a mixture of sucrose and tagatose in triplicate. After 24 h, pH and sugar content of sucrose-added yogurt reached nearly 4.5 and 4.2 respectively, and were lower than those of yogurt with tagatose (above 5.6 and 8.6, respectively). Also, TA of sucroseadded yogurt (1.51%) was much higher than that of yogurt with tagatose (0.59%). There were no significant differences in color value and viable cell count after 24 h. However, the addition of tagatose seems to slow the growth rate of LB more than that of ST. Sensory preference revealed that mixture-added yogurts scored significantly higher in taste (5.90), texture (5.86), and overall acceptability (6.16) than yogurts with tagatose (5.20, 5.02, and 5.36, respectively), but there was no significant difference from the sucrose-added yogurts. In conclusion, tagatose inhibited the fermentation rate, but the mixture of tagatose and sucrose could be used for yogurts with lower calories and glucose index (GI) without a sensory difference from sucrose-added yogurt.