Preparation, characterization and antioxidant activities of acetylated polysaccharides from Cyclocarya paliurus leaves
Introduction
Polysaccharides as natural polymers, widely existed in plants, animals and microorganisms, have a variety of biological properties, such as immunomodulatory, anti-inflammatory and anti-tumour activities (Simpson and Morris, 2014, Yi et al., 2012, Wang et al., 2013; Zhang, Cui, Cheung, & Wang, 2007). Nowadays more and more attention was cast on chemical modification of polysaccharides in order to improve their intrinsic biological functions and to obtain new pharmacological agents with possible medical uses. Acetylation is known to be an important modification method to modify the physicochemical properties, and bioactivities of natural polysaccharides. In the acetylation, parts of the hydroxyl groups of the polysaccharides units have been converted by esterification to acetyl groups (Singh, Nath, & Guha, 2011). Acetylated starch has many unique properties, such as an increase in solubility, swelling power, clarity, reduced the gelatinization temperature, and also decreased the tendency toward retrogradation (Schlemmer, Angelica, & Sales, 2010). Acetylation of mannans or other polysaccharides can be used to control their solubility, water absorbency, hydrophobicity, and physical properties (Penroj, Mitchell, Hill, & Ganjanagunchorn, 2005; Williams et al., 2000, Xu et al., 2010). Song et al. (2013) have also found that acetylated pumpkin polysaccharide showed relevant higher antioxidant activity that of unmodified polysaccharide both in vitro and in a H2O2-induced cell system.
Cyclocarya paliurus (Batal.) Iljinskaja (C. paliurus), known as “sweet tea tree”, belongs to the Juglandaceae family, which grows in mountainous regions. The leaves of C. paliurus have been used to make tea in China because of its unique taste. The leaves possess several health benefits, such as antihypertensive activity, enhancement of mental efficiency and antioxidant activity (Kurihara et al., 2003, Xie et al., 2012). It is also used to inhibit inflammation and prevent hypolipidaemic and diabetes (Xie et al., 2010). In 2013, C. paliurus was approved as new food raw material by National Health and Family Planning Commission of China (Xie et al., 2015). Polysaccharide was considered as one of the effective bioactive components in the leaves of C. paliurus. Great progresses had been made on the studies of composition, physicochemical properties, and bioactivities of C. paliurus polysaccharide in recent years (Huang, Nie, Xie, Han, & Xie, 2009; Xie et al., 2010, Xie et al., 2012). In our previous work (Xie, Liu et al., 2013), one immunoregulatory polysaccharide (CPP), with a molecular weight of 9.0 × 105 Da, was obtained from the leaves of C. paliurus. Structure feature of the purified polysaccharide was investigated by a combination of chemical and instrumental analysis. Preliminary tests showed that CPP exhibited strong growth inhibitory activities on human gastric cancer cells (Xie, Liu et al., 2013), and had potent stimulating effects on murine lymphocyte proliferation (Huang et al., 2009).
The bioactivities of polysaccharides mainly depends on their physicochemical properties, such as degree of substitution, molecular weight, monosaccharide composition, polysaccharide content, type of sugar and functional groups (Melo, Feitosa, Freitas, & de Paula, 2002; Zhang et al., 2007). The structure and antioxidant activity of C. paliurus polysaccharide had investigated in our previous work (Xie et al., 2010, Xie et al., 2012). However, to our knowledge, research on acetylation of C. paliurus polysaccharide has not been reported so far, and the antioxidant activity of the acetylated polysaccharide derivatives still unknown. Therefore, the aim of the present paper was to investigate the acetylation of polysaccharide isolated from the leaves of C. paliurus and to compare their antioxidant activities with unmodified polysaccharide. The new acetylated derivatives were characterized by different methods such as high-performance gel permeation chromatography (HPGPC), high-performance anion exchange chromatography (HPAEC), UV–vis and fourier transform infrared (FT-IR) spectroscopies. Then, their antioxidant activities were investigated by scavenging effect of DPPH radicals and β-carotene–linoleic acid assay.
Section snippets
Plant materials
The leaves of C. paliurus were collected from Jiangxi Province of China. All the samples were authenticated by Prof. Zhihong Fu in Jiangxi University of Traditional Chinese Medicine, China. Voucher specimen was deposited at the State Key Laboratory of Food Science and Technology, Nanchang University, China. The materials were air-dried and ground into a fine powder in a mill before extraction.
Chemicals and reference compounds
Glucose (Glc), xylose (Xyl), arabinose (Ara), rhamnose (Rha), galactose (Gal), ribose (Rib), mannose
Preparation of Ac-CPS
The crude polysaccharide (CP) was isolated from C. paliurus leaves by hot water extraction, ethanol precipitation, deproteinization and lyophilization. Physicochemical analysis showed that CP was an acid hetero-polysaccharide, and its carbohydrate content and uronic acid content were 78.6% (w/w) and 26.2% (w/w), respectively. The chemical composition of C. paliurus polysaccharide and the chromatographic examination of its hydrolysates in our previous work showed the presence of major amounts of
Conclusions
In the present study, three acetylated derivatives with different DS (0.13–0.57) were successfully prepared from the water soluble polysaccharides extracted from the leaves of C. paliurus. This is the first report on the evaluation of the composition and antioxidant properties of acetylated polysaccharides from C. paliurus. The physicochemical and structural study revealed differences in acetylated derivatives and native C. paliurus polysaccharide, which influenced the physicochemical
Acknowledgements
This work was supported by the National Natural Science Foundation of China (Nos. 31471702, 31201297, 31130041), the National Key Technology R & D Program of China (No. 2012BAD33B06), the Major Research plan of the Natural Science Foundation of Jiangxi province, China (No. 20152ACB21004), the Science Funds of Educational Commission of Jiangxi Province, China (No. GJJ14144), and the Objective-Oriented Project of State Key Laboratory of Food Science and Technology, Nanchang University, China (No.
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