Comparative Study on the Structure-Activity Relationship of Dietary Fiber from Different Varieties of Citrus Peel and Pomace

The contents, structures, physicochemical properties and functional characteristics of soluble dietary fiber (SDF), insoluble dietary fiber (IDF) and total dietary fiber (TDF) from the peel and pomace of Nanfeng tangerine, Zigui navel orange and Shatian pomelo were compared and analyzed. The results showed that TDF contents in citrus peel and pomace ranged from 19.96 to 44.26 g/100 g, and IDF/SDF ratios in tangerine peel, tangerine pomace and pomelo pomace were the closest to the recommended dietary ratio (2:1). All dietary fiber samples had obvious characteristic structures of polysaccharides, but their monosaccharide compositions and microstructures were different. Citrus pomace dietary fiber exhibited superior physicochemical properties and functional characteristics to peel dietary fiber, with pomelo pomace dietary fiber showing the best overall performance. Notably, pomelo pomace SDF had a water-holding capacity (WHC) of 28.46 g/g, a water swelling capacity (WSC) of 29.07 mL/g, an oil-holding capacity (OHC) of 3.38 g/g, a cholesterol adsorption capacity (CAC) of 22.56 mg/g, a nitrite ion adsorption capacity (NIAC) of 911.59 µg/g, a glucose adsorption capacity (GAC) of 2.64 mmol/g, and a glucose dialysis retardation index (GDRI) of 28.78% (15 minutes). In conclusion, citrus peel and pomace are good sources of high-quality dietary fiber and can be used as functional food components. This study can provide a theoretical basis for further refining the application of citrus dietary fiber and improving the added value of citrus by-products.