*3.6. Hydration Properties*

The ISMS treatment-induced reduction in particle size, the increase in surface area, and changes in the microstructure and disruption of the crystalline structure could have an effect on the hydration properties of pea fiber, including swelling capacity (SC) and water retention capacity (WRC). SC and WRC of ISMS-treated PeaF is presented in Figure 6A,B, respectively. The value of SC and WRC for the native PeaF was 4.40 mL/g and 4.19 g/g, respectively. ISMS treatment significantly increased the SC and WRC of pea fiber. For instance, the SC of Pre-Pea, ISM-60 PeaF, ISM-90 PeaF, ISM-120 PeaF and ISM-120-T2 PeaF was 9.86, 14.90, 14.21, 13.85 and 16.73 mL/g, respectively. The change trend of WRC was similar with that of SC as the treatment intensity strengthened. In particular, ISMS treatment at 120 MPa for two passes resulted in a 3.8 fold and 2.1 fold increase of SC and WRC, respectively, and this exhibited the largest values (16.73 mL/g and 8.73 g/g). ISMS-treated PeaF occupied a larger sediment volume in Figure 2G owing to its small, loose structure, which implied a greater tendency to absorb water. The transformation from dense to loose microstructure and reduction in size owing to the mechanical effect initiated by ISMS treatment endowed pea fiber with a larger surface area and more water binding sites (polar groups etc.) to the surrounding water [27], thus leading to a strengthened expansion in water and binding with water. Deleris and Wallecan [28] also pointed out that the WRC of fiber suspensions was affected by the crystalline characteristics of cellulose, since water molecules were not able to enter into the crystalline region of the cellulose. That is, disrupting the crystalline structure by ISMS treatment also favored pea fiber to binding water. Intriguingly, the values of WHC and SC were not gradually increased with the increasing of intensity during the ISMS treatment for one pass, which was not inconsistent with other studies [29,30] in which the hydration properties of insoluble dietary fiber were increased or decreased along with the reduction in particle size. The results from this study demonstrated that the hydration properties of pea fiber were dependent on several factors, such as the alteration of the microstructure and crystallinity, and particle size did not play a vital role.

**Figure 6.** Swelling capacity (**A**) and water retention capacity (**B**) of ISMS-treated PeaF. Different letters in (**A**,**B**) indicated significant differences (*p* < 0.05) of hydration properties between samples.

#### *3.7. Oil Holding Capacity*

The intake of low-fat products using dietary fiber as a fat replacement could satisfy the requirement of lowering the amount of ingested fat and calories in the diet, so the capacity of fiber to retain oil is crucial for fibre-rich foodstuffs to exert an effect on cholesterol absorption and removing excess fat from the human body [31]. The OHC of ISMS-treated PeaF is shown in Figure 7. The OHC of native PeaF was 3.01 g/g. Similar to the effect of ISMS treatment on hydration properties, the OHC of fiber was significantly elevated. The OHC of all ISMS-treated PeaF was twice as high as that of native PeaF, and the change trend of OHC was similar to that of the bulk density with the increasing of treatment intensity. After ISMS treatment, an increase in bulk density, a more looser structure, more exposure of the fiber surface area and the disordering of the crystalline structure might increase the capillary attraction and adsorption sites of pea fibre, thus improving the oil-holding

capacity. The increased OHC implied the potential of ISMS-treated PeaF to be used as an ingredient in meat products requiring oil absorption.

**Figure 7.** Oil holding capacity of ISMS-treated PeaF. Different letters in Figure 7 indicated significant differences (*p* < 0.05) of oil holding capacity between samples.

#### **4. Conclusions**

ISMS treatment significantly changed the structure of pea fiber. CLSM images revealed that fibers with a big and compact structure were disintegrated into slim and loose ones. The morphology of pea fiber was changed from compact thick blocks to flimsy crimped flakes. The crystalline structure was also destroyed, owing to the attacking of the original ordered cellulose, thus leading to the reduction of crystallinity. The alterations of the structure were accompanied with the narrowed particle size and the increased bulk density. In the meantime, the SC, WRC and OHC of pea fibers were evidently increased after the ISMS treatment. The improved hydration properties and the OHC of pea fiber was related to destroying the compact structure, providing more surface area and disrupting the crystalline structure by ISMS treatment, since more water binding and oil adsorption sites were exposed. These results suggested that the technology of ISMS facilitated the processing of pea fiber as the ingredient of foodstuffs such as meat products and jams at an industrial level.

**Author Contributions:** Conceptualization, T.D., J.C. and C.L.; methodology, X.H. and T.D.; investigation, X.H.; data curation, X.H., T.D. and M.C.; writing—original draft preparation, X.H., T.D. and R.L.; writing—review and editing, J.S., R.L. and J.C.; visualization, J.S. and M.C.; supervision, W.L. and C.L.; funding acquisition, J.C. and C.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was supported financially by the National Natural Science Foundation of China (32160572, 32101948), and the first batch of high-end talents (Youth) projects of science and technology innovation in Jiangxi Province (grant number jxsq2019201076), and the Research Program of State Key Laboratory of Food Science and Technology, Nanchang University (grant number SKLF-ZZA-201908), China Postdoctoral Science Foundation (grant number 2020M6832211), and Postdoctoral Foundation of Guangxi Academy of Agricultural Sciences (grant number 2020037).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data is contained within the article.

**Acknowledgments:** The authors would like to thank the Centre of Analysis and Testing of Nanchang University and State Key Laboratory of Food Science and Technology for their expert technical assistance.

**Conflicts of Interest:** The authors declare that they have no conflict of interest.

#### **References**

