Purification, antioxidant, hygroscopicity and moisture retention activity of low molecular weight polysaccharide from Litchi chinensis

Abstract: Litchi (Litchi chinensis Sonn.), a tropical/subtropical fruit originally from China, is cultivated all over the world with warm climates. It has become one of the most popular fruits in the world due to its delicious flavor and abundant nutrition. As a good source of minerals, dietary fiber, and phytochemicals, litchi has been employed in traditional Chinese medicine. In addition, litchi has also been used to produce various types of health products and foods, such as medicinal beverages, drinks, or soups. Litchi fruit's pericarp tissues contain a lot of flavonoids, polysaccharides, and various proteins. Polysaccharides are a kind of biomacromolecules composed of more than 10 monosaccharide units, which generally exist in plants, animals, algae and microorganisms such as fungi and bacteria. Some investigations have indicated that Litchi chinensis polysaccharides have strong antioxidative activity and can be explored as novel potential antioxidants. Plant polysaccharides are excellent candidates for health and therapeutics, and searching for polysaccharides with antioxidant activity from plant resources has become a hot research topic. Furthermore, the polysaccharides exhibit good hygroscopicity and moisture retention activity due to the presence of a large number of hydroxyl or carboxyl polar groups, which can form hydrogen bonds with water molecules and cross-linked reticular structure. Antioxidant activity and hygroscopicity and moisture retention activity are important for healthcare to protect mankind from the attack of free radicals and retard the initiation of many chronic diseases. Therefore, it is necessary to more effectively purify and determine the physicochemical properties of polysaccharides from Litchi chinensis. In the current research, crude polysaccharides were extracted from Litchi chinensis to obtain the polysaccharide fraction (PLC). PLC was further purified and a kind of homogenous hetero polysaccharide (PLC-1) was isolated. The physicochemical properties, antioxidant activity, hygroscopicity and moisture retention activity of PLC-1 were analyzed. The polysaccharides of Litchi chinensis were extracted and purified by ultrasonic-assisted extraction, alcohol precipitation, deprotein, decolouring, dialysis, DEAE-cellulose 52 and Sephadex G-100 gel column chromatography. Purity was determined by ultraviolet-visible spectral scanning, spin spectrophotometry and gel filtration chromatography (GPC). The relative molecular mass was determined by high-performance gel permeation chromatography. The monosaccharide composition was analyzed by HPAEC-PAD. The antioxidant activity was evaluated on the basis of DPPH, OH free radical scavenging activity. The hygroscopicity and moisture retention activity was evaluated by adopting the in vitro method. PLC-1 was isolated and purified from Litchi chinensis, which was a kind of homogeneous polysaccharide. The relative molecular mass of PLC-1 was 2.35 × 104 Da. The monosaccharide of PLC-1 included galactose, rhamnose and glucose with a molar ratio of 1.00:3.52:5.89. The antioxidant activity showed PLC-1 had a good dose-effect relationship on DPPH radical and hydroxyl radical in a certain concentration range, and the 50% inhibiting concentration (IC50) of DPPH and hydroxyl radical scavenging activity was 0.41 and 0.31 mg/mL, respectively. The hygroscopicity and moisture retention activity indicated PLC-1 had good effect. Due to the physicochemical properties, antioxidant activity, hygroscopicity and moisture retention activity, PLC-1 has a good prospect in the preparation of functional food and cosmetics.