Figures
Figure 1. Bile acid-binding rate of the seed coat and its water-insoluble fraction of black and yellow soybeans (4%) with 4 mM CA (a), and 2 mM DCA (b). The binding rate of the water-insoluble fraction was adjusted based on the recovery yield relative to the seed coat. Error bars indicate the standard deviation of three measurements, and different letters indicate a statistically significant difference based on a one-way ANOVA with Tukey’s post-hoc test (p < 0.05). CA, sodium cholate; DCA, sodium deoxycholate; CY, cholestyramine; BLK, black soybean seed coat; B-IS, black soybean water-insoluble fraction; YEL, yellow soybean seed coat; Y-IS, yellow soybean water-insoluble fraction; CEL, cellulose.
Figure 2. Bile acid-binding rate of the seed coat and its water-insoluble and water-soluble fractions of black soybean (4%) with 4 mM CA (a), and 2 mM DCA (b). The absolute binding rate of each fraction at 4 %(□) and the adjusted rate based on the recovery yield relative to the seed coat (■) are shown. Error bars indicate the standard deviation of three measurements, and different letters indicate a statistically significant difference based on a one-way ANOVA with Tukey’s post-hoc test (p < 0.05). CA, sodium cholate; DCA, sodium deoxycholate; CY, cholestyramine; BLK, black soybean seed coat; B-IS, black soybean water-insoluble fraction; B-S, black soybean water-soluble fraction; CEL, cellulose.
Figure 3. Bile acid-binding rate of polyphenols (0.033%) with 4 mM CA (a), and 2 mM DCA (b). Error bars indicate the standard deviation of three measurements, and different letters indicate a statistically significant difference based on a one-way ANOVA with Tukey’s post-hoc test (p < 0.05). CA, sodium cholate; DCA, sodium deoxycholate; CY, cholestyramine; CAT, (+)-catechin; EC, (–)-epicatechin; B2, procyanidin B2; C1, procyanidin C1; A2, cinnamtannin A2; C3G, cyanidin 3-glucoside; CEL, cellulose.
Figure 4. Optical absorption spectrum of the acidified methanol solution of the water-insoluble fraction of black soybean seed coat (a), that of yellow soybean seed coat (b), and cyanidin as a control (c).
Tables
Table 1. Anthocyanin contents in the untreated and water-insoluble fractions of black and yellow soybean seed coats
| Anthocyanins (mg/g)† |
|---|
| C3G | D3G | Pt3G | Total†† |
|---|
| †Mean and standard deviation of three measurements are shown based on the weight of the seed coat. ††Total of C3G, D3G, and Pt3G. C3G, cyanidin 3-glucoside; D3G, delphinidin 3-glucoside; P3G, petunidin 3-glucoside; BLK, black soybean seed coat; B-IS, black soybean water-insoluble fraction; YEL, yellow soybean seed coat; Y-IS, yellow soybean water-insoluble fraction; n.d., not detected. |
| BLK | 32.11 ± 1.54 | 3.24 ± 0.28 | 1.36 ± 0.10 | 36.70 ± 1.88 |
| B-IS | 0.26 ± 0.01 | 0.04 ± 0.01 | 0.01 ± 0.00 | 0.31 ± 0.01 |
| YEL | n.d. | n.d. | n.d. | n.d. |
| Y-IS | n.d. | n.d. | n.d. | n.d. |
Table 2. Monomer and oligomer contents of flavan-3-ol in the untreated and water-insoluble fractions of black and yellow soybean seed coats
| Flavan-3-ol monomers, oligomers (mg/g)† |
|---|
| CAT | EC | B2 | C1 | A2 | Total†† |
|---|
| †Mean and standard deviation of three measurements are shown based on the weight of the seed coat. ††Total of CAT, EC, B2, C1, and A2. CAT, (+)-catechin; EC, (–)-epicatechin; B2, procyanidin B2; C1, procyanidin C1; A2, cinnamtanninA2; BLK, black soybean seed coat; B-IS, black soybean water-insoluble fraction; YEL, yellow soybean seed coat; Y-IS, yellow soybean water-insoluble fraction; n.d., not detected; Trace, below the limit of quantification. |
| BLK | 0.20 ± 0.02 | 2.34 ± 0.30 | 2.72 ± 0.59 | 0.79 ± 0.17 | 0.37 ± 0.11 | 6.42 ± 1.15 |
| B-IS | 0.04 ± 0.00 | 0.20 ± 0.00 | 0.14 ± 0.03 | 0.04 ± 0.01 | 0.04 ± 0.02 | 0.45 ± 0.02 |
| YEL | n.d. | Trace | Trace | n.d. | n.d. | Trace |
| Y-IS | n.d. | n.d. | n.d. | n.d. | n.d. | n.d. |
Table 3. Polyphenol contents of the acidified methanol solution of the water-insoluble fraction of black and yellow soybean seed coats
| Total cyanidins (mg/g, cyanidin equivalent) | Total proanthocyanidins (mg/g, CAT equivalent) |
|---|
| The means of two measurements are shown based on the weight of the seed coat. The total cyanidins were calculated by the absorbance (555 nm), and the total proanthocyanidins were determined using the vanillin sulfate method. CAT, (+)-catechin; B-IS, black soybean water-insoluble fraction; Y-IS, yellow soybean water-insoluble fraction; Trace, below the limit of quantification. |
| B-IS | 66.8 | 1.3 |
| Y-IS | Trace | Trace |