*3.4. The Adsorption Capacity of HPIDF/F-HPIDF*

#### 3.4.1. WHC, WSC, and OHC of HPIDF/F-HPIDF

The WHC and WSC of HPIDF/F-HPIDF are shown in Figure 6a. Although the WHC and WSC of HPIDF are much higher than other IDFs [40,41], those of F-HPIDF (19.17 g/g, 24.83 mL/g) were still higher than HPIDF (*p* < 0.01). Carboxyl (-COOH) and hydroxyl (-OH) are the common polar functional groups in IDFs. The larger specific surface area and smaller particle size represented more polar groups in contact with the environment. The excellent water absorption of F-HPIDF was consistent with the previous results of the structure changes.

**Figure 6.** WHC, WSC and OHC of HPIDF/F-HPIDF. (**a**: WHC & WSC; **b**: OHC; \*: *p* < 0.05; \*\*: *p* < 0.01).

The OHC of HPIDF/F-HPIDF is shown in Figure 6b. The mechanisms of dietary fiber to adsorb saturated and unsaturated oils are different. So, we chose soybean oil and lard to determine the different OHCs of HPIDF/F-HPIDF. The result shows that the OHC of F-HPIDF for unsaturated fat (6.82 g/g) was lower than that of HPIDF (*p* < 0.05), however not different (17.77 g/g) from that for saturated fat (*p* > 0.05). Common hydrophobic groups include C-H stretching (-CH3 or =CH2), ethers (C-O), etc. This just showed that the hydrophobic groups in HPIDF were exposed less with the progress of fermentation, which might be attributed to the decomposition of hemicellulose during the progress described in 3.3. Acetyl should be considered as the characteristic functional group of hemicellulose [42], the decomposition of hemicellulose might lead to the loss of acetyl, which could be the result of the decrease of OHC. In contrast, saturated fat (such as lard) does not contain unsaturated bonds, which leads to a weaker dependence on acetyl than saturated fat. To prevent excessive absorption of fat by the intestine, a higher OHC is desirable. According to the fermentation mode of HPIDF in this study, we may try to modify the non-hemicellulose components so that they will not be decomposed by the gut flora while maintaining a high content of hydrophobic groups.
