Abstract
Three fractions of water-soluble polysaccharide conjugates, coded as TPC-1, TPC-2, and TPC-3, were isolated and purified from low-grade green tea ( Camellia sinensis) by absorbent chromatography and ion exchange chromatography. Their chemical and physical characteristics were determined by chemical methods, gas chromatography and size exclusion chromatography with laser light scattering. Deoxyribose assay, photoreduction of Nitro Blue Tetrazolium (NBT) assay and lipid peroxidation inhibition assay were applied to test the antioxidant activities of tea polysaccharide conjugates in vitro. The results indicated that the three polysaccharide conjugates were heteropolysaccharides bounded with protein. TPC-1 was composed of l-arabinose (Ara), d-ribose (Rib), d-xylose (Xyl), d-glucose (Glc), d-galactose (Gal) and d-mannose (Man). TPC-2 was only composed of four monosaccharides: Ara, Rib, Glc and Man. There was no Man detected in TPC-3. The protein contents of TPC-1, TPC-2, and TPC-3 were 2.8%, 3.8% and 4.0% and the molecular weights were 26.8 × 10 4, 11.8 × 10 4, 4.2 × 10 4, respectively. TPC-3 showed the highest antioxidant activities among the three fractions of polysaccharide conjugates, with an IC 50 of 182 μg/ml for the deoxyribose assay, and 93 μg/ml for the photoreduction of NBT assay, values which were lower than those of TPC-1 and TPC-2 ( P < 0.01). The effects of the molecular weight and protein content of the polysaccharide conjugates on the improvement of the bioactivities appeared to be significant.
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