Abstract
Ultrasound-assisted enzymatic treatment was used to treat Newhall navel orange peel and residue, and then the structural, physicochemical and functional properties of extracted soluble dietary fibers (SDF) and insoluble dietary fibers (IDF) were investigated. The structural properties were determined using scanning electron microscopy, X-ray diffraction, FT-IR and monosaccharide composition. Among these dietary fibers, residue-SDF showed a more complex structure, while peel-IDF exhibited a looser structure. Four samples showed representative infrared spectral features of polysaccharides, typical cellulose crystalline structure and diverse monosaccharide composition. Furthermore, residue-IDF exhibited higher oil-holding capacity (2.08 g/g), water-holding capacity (13.43 g/g) and nitrite ion adsorption capacity (NIAC) than other three samples, and residue-SDF showed the highest swelling capacity (23.33 mL/g), cation exchange capacity (0.89 mmol/g) and cholesterol adsorption capacity (CAC) among these dietary fibers. In summary, this study suggests that the residue-SDF and residue-IDF could be used as the ideal dietary fibers for application in the functional food industry.
Highlights
Orange (Citrus L.) fruit is one of the most important fruits in the world
Compared with soluble dietary fibers (SDF) and insoluble dietary fibers (IDF) of Newhall navel orange peel, the Newhall navel orange residue had the higher SDF content (15.05%) and IDF content (79.10%), which may be attributed to the disruption of the glycosidic linkages in dietary fiber under ultrasound, causing in orange peel a loss of SDF, IDF, hemicellulose and cellulose [24]
It could be found that DF of residue possessed higher molecular weight than DF of peel, which indicated that the molecular weight of DF in orange peel was significantly affected by ultrasound-assisted enzymatic method
Summary
Newhall navel is the main variety of navel orange, which is famous for its large seedless fruit, thin skin, bright color and fragrant, sweet taste. Because of its high vitamin content and rich aroma characteristics, it is well-received by consumers. In addition to a small number of oranges for processing, most oranges are used for marketing fresh. A large number of by-products are formed during processing and daily consumption [1], such as peel and residue, accounting for 20~35% of the whole fruit mass. Peel and residue are main by-products of orange, which are rich in dietary fiber (DF). In order to better use the by-products of Newhall navel orange, it is necessary to investigate the structural, physicochemical and functional properties of dietary fiber exacted from Newhall navel orange peel and residue
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