Extraction, characterization, and antioxidant properties of cell wall polysaccharides from the pericarp of Citrus Reticulata cv. Chachiensis

The pericarp of Citrus reticulata cv. Chachiensis (PCRC) had been used as a traditional herbal medicine in southeast and eastern Asia, and it was also an important source of nutraceuticals and functional food ingredients. In the present study, the cell wall polysaccharides were sequentially extracted from PCRC using different solvents, resulting in five pectic fractions and two hemicellulose fractions, namely water-soluble pectin (WSP), hot water-soluble pectin (HWSP), chelator-soluble pectin (CSP), diluted acid-soluble pectin (HSP), sodium carbonate-soluble pectin (NSP), 1 mol/L KOH soluble hemicellulose (KSH-1) and 4 mol/L KOH soluble hemicellulose (KSH-2). The seven fractions were characterized in terms of composition, structure, thermal, rheological, and antioxidant properties. The pectin fractions were classified as high-methoxy pectin with a degree of methyl esterification (DM) between 56.89% and 62.20%. Ammonium oxalate extraction provided the CSP fraction with the highest content of galacturonic acid (75.18%) and the lowest degree of acetylation (0.03). HWSP was considered to be an aggregative of homogalacturonan (HG) and rhamnogalacturonan I (RG-I) containing side chains of galactans and arabinans. Thermal analysis indicated that HWSP had the highest thermal stability than other fractions. All fractions exhibited the characteristics of non-Newtonian fluids, with NSP showing the highest apparent viscosity. Assays for antioxidant activities suggested WSP had the highest DPPH radical scavenging activity while NSP had the highest hydroxyl radical scavenging activity. The result could be a good basis for the applications of cell wall polysaccharides, especially pectin, of PCRC in the preparation of functional food products.