**3. Results**

#### *3.1. Inhibition of Pancreatic α-Amylase*

As shown in Figure 1, the amount of maltose released from all of the flours was observed after 10 min of incubation. There was a significant reduction for the release of maltose after mixing the potato, rice, glutinous rice, wheat, corn, and cassava flour with 1% and 2% (*w*/*v*) CTE, compared with the control (*p* < 0.05).

**Figure 1.** *Cont.*

**Figure 1.** The amount of maltose released from (**a**) potato flour, (**b**) rice flour, (**c**) glutinous rice flour, (**d**) wheat flour, (**e**) corn flour, and (**f**) cassava flour when combination with the different concentrations of CTE against pancreatic α-amylase activity at 10 min. The results are expressed as mean ± standard error of the mean (SEM), *n* = 4. The different letters denote statistically significant differences in mean values. (*p* < 0.05) Mean values with the same superscript letters (a or b) were similar and no statistically significant differences were observed for these samples. CTE—*Clitoria ternatea* L. flower extract.

The percentage of pancreatic α-amylase inhibitory activity after mixing the CTE into flour is shown in Table 1. The increased percentage of pancreatic α-amylase inhibitory activity was concomitant with the increased concentration of CTE. The results demonstrated that the mixture of potato, rice, glutinous rice, wheat, corn, and cassava flours with 1% and 2% (*w*/*v*) CTE resulted in a higher pancreatic α-amylase inhibitory activity than that of the 0.5% (*w*/*v*) of CTE (*p* < 0.05). At 2% (*w*/*v*) CTE, the potato flour had the highest percentage of pancreatic α-amylase inhibitory activity, followed by glutinous rice, rice, wheat, corn, and cassava, respectively.


**Table 1.** The percentage of pancreatic α-amylase inhibitory activity of CTE.

The results are expressed as mean ± standard error of the mean (SEM), *n* = 4. CTE—*Clitoria ternatea* L. flower extract.

#### *3.2. In Vitro Starch Digestibility and Predicted Glycemic Index (pGI)*

The results of in vitro starch digestibility of flour at different concentration of CTE are shown in Figure 2. The incorporation of CTE decreased the glucose released from flour. The results demonstrated that the amount of glucose released from the mixture of CTE and flours was lower than the control. The addition of 2% (*w*/*v*) CTE into flour significantly caused the highest inhibition of starch digestibility.

**Figure 2.** The amount of glucose released from (**a**) potato flour, (**b**) rice flour, (**c**) glutinous rice flour, (**d**) wheat flour, (**e**) corn flour, and (**f**) cassava flour when in combination with the different concentrations of CTE under in vitro digestibility during 180 min. The value of 0.5%, 1%, and 2% (*w*/*v*) represent the concentration of CTE, respectively. The results are expressed as mean ± standard error of the mean (SEM), *n* = 4. The different letters denote statistically significant differences in mean values. (*p* < 0.05) Mean values with the same superscript letters (a, b or c) were similar and no statistically significant differences were observed for these samples.

Table 2 represents an interpretation of the hydrolysis index (HI) and the predicted glycemic index (pGI) of all of the samples. The HI and pGI of potato, rice, glutinous rice, wheat, corn, and cassava flour with 0.5%, 1%, and 2% (*w*/*v*) of CTE were significantly lowered when compared with the control (*p* < 0.05). Interestingly, the addition of 2% (*w*/*v*) CTE caused the reduction of pGI of the glutinous rice, wheat, and cassava flour from the high value to the medium value (GI < 70).


**Table 2.** The hydrolysis index (HI) and predicted glycemic index (pGI) of the flours with CTE.

The results are expressed as mean ± standard error of the mean (SEM), *n* = 4. The different letters denote statistically significant differences in mean values. (*p* < 0.05) Mean values with the same superscript letters (a, b, or c) were similar and no statistically significant differences were observed for these samples.

#### *3.3. Starch Fraction*

The RDS, SDS, and undigested starch of flours are presented in Figure 3. The RDS content of six flours mixed with at 2% (*w*/*v*) CTE significantly decreased when compared with the control (*p* < 0.05). The addition of CTE at 0.5%, 1%, and 2% (*w*/*v*) caused a reduction in the SDS content of glutinous rice, corn, and cassava flour (*p* < 0.05). However, the CTE did not alter the SDS content of potato flour. The observed results also found that only the glutinous rice flour significantly increased the undigested starch with the addition of CTE (*p* < 0.05). Table 3 shows the correlation between the concentration of CTE and undigested starch of flour. The undigested starch of the wheat and cassava flour correlated significantly and positively with the concentration of CTE (*r* = 0.650 and 0.758, respectively; *p* < 0.05). However, no significant correlation was observed between the concentration of CTE and other flours, including potato flour, rice flour, glutinous rice flour, and corn flour.

**Figure 3.** *Cont.*

**Figure 3.** Starch fraction after in vitro digestibility of (**a**) potato flour, (**b**) rice flour, (**c**) glutinous rice flour, (**d**) wheat flour, (**e**) corn flour, and (**f**) cassava flour when in combination with the different concentration of CTE. The value of 0.5%, 1%, and 2% (*w*/*v*) represent the concentrations of CTE, respectively. The results are expressed as mean ± standard error of the mean (SEM), *n* = 4. The different letters denote statistically significant differences in mean values. (*p* < 0.05) Mean values with the same superscript letters (a, b or c) were similar and no statistically significant differences were observed for these samples. RDS: rapidly digestible starch; SDS: slowly digestible starch.

**Table 3.** Correlation coefficients calculated between the concentrations of *Clitoria ternatea* (CTE) and undigested starch contents after in vitro digestion.


#### *3.4. In Vitro Digistibility of Bread*

Cross sections of bread made from wheat flour and CTE are shown in Figure 4. The in vitro starch digestibility of wheat bread with 5%, 10%, and 20% (*w*/*w*) of the CTE are presented in Figure 5a. The amount of glucose released from the bread with CTE was lower than that of the control. The addition of 5%, 10%, and 20% (*w*/*w*) CTE into wheat bread significantly reduced the rate of starch digestion after 120, 150, and 180 min of incubation (*p* <0.05). As shown in Figure 5b, the iAUCs for the glucose release of bread incorporated with 5–20% (*w*/*w*) CTE were 8136 ± 82, 8997 ± 42, and 7363 ± 386 mg/dL·min, respectively (the control = 11,364 ± 172 mg/dL·min). The pGI of the bread with 5–20% (*w*/*w*) CTE was 65.40 ± 0.26, 68.11 ± 0.13, and 62.96 ± 1.22, respectively, whereas the wheat bread had the pGI of 75.58 ± 0.54.

**Figure 4.** The cross section of bread made from wheat flour and CTE.

**Figure 5.** The amount of glucose released from wheat bread after in vitro digestibility (**a**) and incremental area under the curve (iAUC) for glucose release (**b**) when in combination with the different concentrations of CTE. The values of 5%, 10%, and 20% (*w*/*w*) represent the concentration of CTE, respectively. The results are expressed as mean ± standard error of the mean (SEM), *n* = 4. The different letters denote statistically significant differences in mean values. (*p* < 0.05) Mean values with the same superscript letters (a, b or c) were similar and no statistically significant differences were observed for these samples.
