## 3 Results and Discussion
### In Vitro Digestibility  
#### 3.5.1 Starch Digestibility  
RDS can be digested and absorbed and release energy quickly in the oral cavity and small intestine. Although SDS is digested slowly, it can be absorbed completely in the small intestine and maintain blood glucose homeostasis for a long time. RS cannot be digested in the small intestine but can be utilized by the intestinal flora in the large intestine, which has the effects of preventing colon cancer, lowering the glycemic index, and regulating serum cholesterol levels [21]. The contents of RDS, SDS, and RS were calculated according to the methods mentioned in Section 2.9.1. As shown in Table 6, with the increase of DF addition, the content of RDS and SDS decreased gradually, and the content of RS increased gradually. In general, the RS content is relevant to food processing, temperature, storage conditions, starch gelatinization, and coagulation. Therefore, starch granules of steamed millet flour would be destroyed by heat treatment, then the release of amylose and the increase of linear-linear and linear-branched bonding might cause a rise in the RS content [13]. With the increase of DF content, RDS and SDS declined gradually; in contrast, RS increased. [PERSON] et al. also found higher RS content in an in vitro wheat starch gel digestion model with added dietary fiber, which is consistent with the current research [22]. The results showed that partial substitution with millet flour and DF was beneficial for hypergly people in comparison with steamed bread made from pure wheat flour. Figure 1 shows that with the extension of hydrolysis time, the starch hydrolysis rate of the steamed bread presented a rapid increase within 30 min and thereafter a relative plateau, which is similar to the trend of starch hydrolysis kinetics of wheat flour gel with apple dietary fiber [22]. The starch hydrolysis rate of the reference food (white bread) reached 75.03%, while the rates for WF and WF&MF were 60.72% and 50.65%, respectively, at the end of digestion (180 min). In addition, the starch hydrolysis rate was decreased with the addition of DF, and the rate for the 10% DF group dropped to 40.83%; this might be because the starch granules were wrapped in the pores of DF, thus blocking the reaction between starch and amylase [23]. Furthermore, DF could compete for water molecules with starch as a result of its strong water binding capacity and cause a reduction in the starch gelatinization degree and starch hydrolysis rate in the steamed bread [24], which coincides with the increase of RS content found above. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **Appearance** & \multirow{2}{*}{**Porosity**} & \multirow{2}{*}{**Elasticity**} & **Mouth** & \multirow{2}{*}{**Flavor**} & \multirow{2}{*}{**Color**} & **Specific** & **Total** \\  & **Shape** & & & & & & **Volume** & **Points** \\ \hline WF & 13 & 12 & 18 & 9 & 14 & 14 & 10 & 90 \\ WF\&MF & 13 & 13 & 17 & 8 & 14 & 13 & 8 & 85 \\
2\% DF & 12 & 12 & 16 & 8 & 13 & 12 & 7 & 80 \\
4\% DF & 12 & 11 & 15 & 8 & 11 & 10 & 6 & 73 \\
6\% DF & 11 & 10 & 13 & 8 & 11 & 8 & 5 & 66 \\
8\% DF & 11 & 11 & 10 & 7 & 9 & 7 & 4 & 59 \\
10\% DF & 10 & 9 & 9 & 6 & 8 & 6 & 3 & 51 \\ \hline \hline \end{tabular}  
Values are represented as means. Sample WF was the control.  
\end{table} 
Table 5: Sensory evaluation of steamed bread with steamed millet flour and DF. The area under the starch hydrolysis rate curve (AUC) of samples was calculated; the AUCs of WF, WF with MF, and WF with MF and 2% DF were 8717.83, 7826.25, and 6951.20, respectively. As the amount of added DF increased, the AUC gradually decreased. According to the AUC of the reference food (white bread) (10,878.25), the starch hydrolysis index (HI) values of WF, WF with MF, and WF with MF and 2% DF were calculated to be 80.14, 66.98, and 63.90, respectively, and the glycemic index (GI) values were 83.70, 76.48, and 74.79, respectively. Similarly, HI and GI presented a significant downward trend with the addition of DF (\(p<0.05\)).