Preparation, characteristics, and antioxidant activities of carboxymethylated polysaccharides from Paeonia x suffruticosa petals

Two carboxymethylated polysaccharides (CPSP30, CPSP60) were obtained from the petals of Paeonia x suffruticosa Andrews (PSP30, PSP60, respectively) with different molecular weight. Chemical characterization, morphological properties and antioxidant activities of PSP and CPSP were determined. PSP were mainly composed of galactose, glucose, fructose and galacturonic with different molar percentages. CPSP were mainly composed of arabinose, galactose, glucose with different molar percentages. The signals of carboxymethyl groups were found in Fourier transform infrared spectroscopy (FT-IR) and 13C nuclear magnetic resonance (NMR) spectra. Scanning electron microscopy (SEM) indicated that the original polysaccharides had a smooth surface, while the modified polysaccharides had an irregular lamellar structure. Thermal analysis indicated that the modified polysaccharides (CPSP30, CPSP60) presented higher thermal stability than the original polysaccharides. All polysaccharides presented typical structures of non-crystalline compounds. Carboxymethylation did not destroy the triple-helical structures of the polysaccharides. With its lower molecular weight, CPSP30 had higher scavenging 1,1-diphenyl-2-picrylhydrazyl (DPPH), OH, and Fe2+ chelating ability than PSP30. The scavenging DPPH and OH abilities of both derivatives were higher than that of original polysaccharides. This study demonstrates that carboxymethylation improved the solubilities and antioxidant abilities of the original polysaccharides, thus enhancing their potential for application in food and pharmaceutical industry.