## 3 Results  
### Effects of TB on pH, Acidity, and Apparent Viscosity of Yogurt  
The appearance of common yogurt and TB yogurt is shown in Scheme 1. It is clear that common yogurt appeared a milky white color, while TB yogurt exhibited a light yellow color and TB was well-dispersed in it. The pH of yogurt is an important indicator of its quality. The effect of TB content (g) on pH is shown in Figure 1A. The pH values of all yogurt groups exhibited a clear decreasing trend over fermentation time, because lactic acid bacteria such as _Lactobacillus bulgaricus_ and _Streptococcus thermophilus_ can exhibit rapid reproduction during fermentation and ferment lactose to lactic acid [4]. The pH of yogurt decreased rapidly within 2 h and showed a positive correlation upon the introduction of TB. A slow decline was observed at the fermentation duration of 2-5 h. The results show that the pH was higher in the plain yogurt than that in the TB-treated yogurt. Furthermore, after 5 h of fermentation, the pH  
Figure 1: Flowchart for manufacturing process of common yogurt and TB yogurt. value of all treatments were in the range of 4.38-4.57, and yogurt (100 mL) with 10 g of TB showed the lowest pH value (4.38). The acidity showed an overall increase in all groups over the fermentation time (Figure 1B), due to both sugar consumption and lactate accumulation acidifying the milk. The initial acidity difference among the adjacent groups was weak when the amount of TB was less than 10 g, and it significantly enlarged upon the addition of TB beyond 10 g. There was a rather slow increase in the titration acidity in the first 2 h of fermentation, followed by a fast-rising trend in the first 2 h and a gradually slowing down trend in the last 1 h. It was obvious that the acidity increased in response to the increasing TB concentration, and the yogurt finally displayed remarkable acidity differences with the introduction of TB. The apparent viscosity is an extremely important factor in evaluating the yogurt, as it represents the consistency and stiffness of yogurt, and also reflects the taste, tissue shape, and stability [19]. The apparent viscosities of all yogurt samples increased over the fermentation time throughout the duration of 5 h (Figure 1C), which might be attributed to the structural rearrangement of yogurt protein gel and the water-retaining action of hydrophobic protein. The apparent viscosity of the yogurt samples barely changed among groups within the first 2 h. The most dramatic rise occurred after incubation for 2 h, and the apparent viscosity peaked at the end. The sample containing 8 g of TB had the highest apparent viscosity performance (0.68 Pa-s) after fermentation for 5 h. The apparent viscosity enhancement might be associated with the presence of fibers in the TB-added yogurt, which resulted in the improvement and rearrangement of the casein gel network structures as well as the suppression of shrinkage and whey expulsion [16]. Furthermore, the apparent viscosity of yogurt is associated to the production of acid. When the acidity rises, the protein in the milk forms a firmer gel, causing the higher apparent viscosity in  
Figure 1: pH (**A**), total tittatable acidity (**B**), apparent viscosity (**C**), and bacteria count (**D**) of yogurt with different TB addition during fermentation. yogurt [20]. It is also worth noting that the increasing trend of apparent viscosity gradually slowed down, most likely due to increasing TB addition. These findings are in good agreement with previous studies on apples, wheat fibers and rice bran [21]. Previous research has found that probiotic yogurt samples incorporating fiber had greater viscosity and acidity, and lower pH and syneresis when compared with plain yogurts [7]. The considerable decrease in pH and the increase in acidity and apparent viscosity should be owing to the increased metabolic activities of fermentative bacteria, which initiate the accumulation of metabolites such as phenolics, flavonoids, and organic acids [22].