| Tangerine peel is a kind of dried peels from mandarin (Citrus reticulate Blanco) and other improved varieties of tangerines, which is taken traditionally as a medicine name Chenpi in China. Lots of studies have been carried out on mandarin essential oil and flavones. Polysaccharides present in Chenpi have not been investigated adequately. This paper focuses on the isolation, purification, structure characterization and antioxidant activity of the polysaccharides in tangerine peel. The chief results are showed as follows:1. By L9(34) orthogonal design test , the extractive conditions of water-soluble polysaccharides in Tangerine peel were investigated. The optimum conditions are as follow: solid-liquid ratio of 1:10,temperature of 100℃and time of 6 hours. The extraction efficiency of polysaccharides in Tangerine peel by ultrasonic method was 7.61%. The crude polysaccharides was discolored by polyamide, removed protein by Sevag way and dialyzed to obtain pure polysaccharides PSP. The content of total carbohydrate, galacturonic acid, monosaccharide and protein in PSP were 17.80%, 28.38%, 3.59% and 0.99% respectively. The result ofβ-elimination reaction indicated that the chain of polysaccharide and protein were connected by O-linked covalent bond. The congo-red reaction indicated that triple helix structure was occurred in PSP molecule.2. By DEAE-cellulose column chromatography, PSP was isolated into four fractionates, namely PSM, PSE, PST and PSF. Through the analysis of GPC, it was concluded that the four fractionates were all the homogenous polysaccharide fractions. And the MW of PSM, PSE, PST and PSF were 0.8×104 Da, 1.1×105 Da, 2.1×105 Da and 2.1×105 Da. The specific rotations of them were–128°, +145°, +201°and +189°respectively. By monosaccharide composition analysis, PSM was mainly composed of glucose and galactose, with a radio of 1:1.1; PSE was mainly composed of arabinose and galactose, with a radio of 1:1.2; PST was mainly composed of rhamnose; PSF was mainly composed of rhamnose, arabinose and galactose, with a radio of 1.5:1:1.1. With TLC analysis the tangerine peel polysaccharides were mainly composed of six neutral sugars, in which rhamnose, arabinose, glucose and galactose were detected as the major sugar constituents. It was indicated by FI-IR that PSM was a low molecular weight polysaccharide, which was mainly composed of pyranose and hadβepimer. PSE, PST and PSF were three kinds of similar polygalacturonic acids which had methyl esterification.3. A fraction PST-a was isolated from PST by SephadexG-75 column chromatography. GPC and agarose gel electrophoresis showed that PST-a was a uniform fraction and the relative molecular weight was 1.0×105 Da. The structure of PST-a has been characterized by means of GC, IR, 1H NMR and 13C NMR. The results revealed that PST-a possessed a backbone chain of 1→4-linkedα-D-galacturonic acid units, which had acetyl groups binding at 2-O- and 3-O-GalA and methyl esterification of carboxyl groups GalA. Rhamnose, arabinose and galactose existed as pyranoid in the side chain or at the end group.4. The free radical scavenging activity of polysaccharides and flavones from tangerine peel were evaluated by determining the discoloration of the DPPH radicals and the OH radicals generated in the Fenton reaction. Ascorbic acid was used as positive control. The experiments showed that both the polysaccharides and the flavones had strong inhibiting effect to DPPH·and OH·, the effect got stronger with increasing the contents. The SC50 values indicated that the scavenging capacity of flavones was close to ascorbic acid. The scavenging capacity of polysaccharides was lower than the flavones and ascorbic acid. |
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