Dietary fibers can be defined as health beneficial carbohydrate polymers that resist digestion by small intestinal enzymes (Garcia-Amezquita et al. 2018). In recent years, dietary fibers have received great attention due to various health benefits such as hypoglycemic and hypolipidemic effects. However, because of the excessive emphasis on sensory and taste, bulk foods such as rice and flour products are over-processed, and lots of dietary fibers are removed, which results in insufficient intake in the human body and thus leads to many negative effects. Therefore, some manufacturers supplement the food with dietary fibers by exogenous addition to increase its health effects.
As the seventh essential nutrient (Waliullah et al. 2021), dietary fibers are conventionally classified into insoluble dietary fibers (IDFs) and soluble dietary fibers (SDFs) based on their solubility. IDFs include cellulose, hemicellulose, and lignin, etc., whereas SDFs include pectin, β-glucan, oligosaccharide, inulin, plant mucilage, etc. (Chawla and Patil 2010). It was found that SDFs had stronger physiological functions compared with IDFs in many aspects (Bader Ul Ain et al. 2019), including adjustment of blood cholesterol levels, reduction of cardiovascular disease risk, prevention of gastrointestinal problems, promotion of bacterial metabolic activities, prevention of type 2 diabetes, antioxidants and antitumor (Zhang et al. 2011b; Mudgil 2017; Ahmed et al. 2011; Cui and Zhu 2021). As far as functional food market is concerned, the development of SDF-fortified foods is more promising. Meanwhile, SDFs possess more advantages than IDFs in physicochemical properties (Gao et al. 2015), with higher ability to form gels and act as emulsifiers, and to impart texture, color, sensory, shelf life, thickening and stabilizing (Jia et al. 2019; Xie et al. 2017; Waliullah et al. 2021; Nandi and Ghosh 2015) properties to foods.
The properties of SDFs, including water solubility, water-holding capacity, emulsifying activity, swelling capacity, viscosity, absorption capacity, are decisive to their application scopes. Among them, water solubility, water-holding capacity and swelling capacity reveal the interaction between SDFs and water, and exert influences in the physiological functions and applications. SDFs with high water solubility can be used in beverages or formulated high-fiber foods. SDFs with high water-holding capacity can be applied in meat products, baked foods, flour products, or be used as fat substitutes in sausages (Kurek and Wyrwisz 2015; Yang et al. 2017; Kim and Paik 2012), and those with good emulsifying activity are suitable for cream and ice cream products. SDFs with favorable viscosity and swelling capacity increase satiety, which can be used in slimming products such as meal replacement shakes, solid beverages and chewable tablets. Furthermore, it is confirmed that SDFs can inhibit α-amylase activity, affect the release of glucose from starch (Cheng et al. 2017), and absorb cholesterol, which show their application potential in functional foods to lower or stabilize blood sugar and blood lipid levels.
Over the past few years, the demands for healthy food have stimulated the development of innovative fiber-rich foods and vastly broadened the application scopes of SDFs (Lopez-Marcos et al. 2015). However, the physicochemical and functional properties of SDFs from different plant sources are quite different, affecting their applications in food industry. Therefore, it is necessary to investigate the properties of SDFs so as to provide basic data for better utilization. However, so far very few studies have systematically compared the properties of different plant-derived SDFs. In this study, industrialized SDFs derived from konjac, apple, chicory, flaxseed, orange, psyllium seed, soybean and oat were selected, and the properties of the SDFs, including structural properties (molecular weight, monosaccharide composition, fourier transform infrared spectroscopy and X-ray diffraction), physicochemical properties (water solubility, water-holding capacity, swelling capacity, emulsifying activity and stability, rheological properties and gel properties), α-amylase inhibitory activity and cholesterol absorption capacity were systematically evaluated and compared, and thus, advantages and disadvantages of SDFs can be clarified, which can provide data to support the production of fiber-rich foods with higher consumer acceptability and health benefits.