Preparation,characterization And Antioxidant Activity Of Selenium Polysaccharide In Se-enriched Tea

Selenium（Se）is one of the essential trace elements in human body,which has been proved to have many biological activities.Polysaccharides,as one of the natural active ingredients,have preventive and therapeutic effects on many diseases.In recent years,the research on polysaccharides and selenium has been studied more in-depth,but how to combine polysaccharides and selenium into selenium polysaccharides is still in its infancy both at home and abroad.In this paper,the selenium-enriched tea polysaccharides（SeTPS）were extracted by subcritical water extraction from crude leaf of tea with high selenium content.Four different fractions of polysaccharides were obtained by purified with DEAE-52and Sephadex G-100 column.SeTPS-1 and SeTPS-2 fractions were selected to characterize their structures.Their reducing power,ABTS free radical scavenging ability,hydroxyl radical scavenging ability and DNA damage protection activity induced by hydrogen peroxide were also explored.The main results were as follows:1.The atomic fluorescence spectrometry and phenol sulfuric acid method were used to determine the selenium content and polysaccharide yield in one bud and one leave,one bud and two leaves,three or four leaves and old leaves of tea respectively.The results showed that the order of selenium content and polysaccharide yield in different parts of tea was:old leaves>three leaves or four leaves>one bud and two leaves>one bud and one leaf,indicating that the accumulation of selenium and polysaccharide took some time.Therefore old leaf of tea with higher selenium content and polysaccharide yield was selected as raw material,and the process of extracting polysaccharides from selenium-enriched tea by subcritical water was optimized by response surface methodology.The results showed that the optimization of extraction conditions were liquid-to-material ratio of 30:1 m L/g,subcritical temperature of 150 ^oC and subcritical time of 12 min.Under these conditions,the yield of polysaccharides from selenium-enriched tea was 5.86±0.23%.which indicated that the subcritical water method was an efficient extraction technology of polysaccharide.2.The crude polysaccharides from selenium-enriched tea extracted by subcritical water method were purified by DEAE-52 and Sephadex G-100 columns.The main fractions SeTPS-1 and SeTPS-2 were collected and their structures were studied.The total carbohydrate content in SeTPS-1 and SeTPS-2 was 96.47%and 68.28%,respectively.The selenium content was 23.5μg/g and 13.47μg/g,respectively.SeTPS-1 was neutral sugar without uronic acid,and the content of uronic acid in SeTPS-2 was 15.77%.The UV test proved that both SeTPS-1 and SeTPS-2 did not contain protein.The average molecular weight of SeTPS-1 and SeTPS-2 was 1.7×10⁴Da and 1.3×10⁴Da by HPGPC analysis.GC results indicated that SeTPS-1 was composed of glucose and galactose with a molar ratio of80.13:2.34.SeTPS-2 consists of arabinose,glucose,galactose,galacturonic acid composition,and the molar ratio was 2.04:48.83:3.21:1.30.The fourier infrared spectroscopy showed that SeTPS-1 and SeTPS-2 have asymmetric Se=O stretching vibration peak at 763 cm^-1 and the O-Se-O peak at 1025 cm^-1,selenized polysaccharides are actually present in SeTPS-1 and SeTPS-2.The scanning electron micrographs demonstrated SeTPS-1 and SeTPS-2 was flaky and had a smooth surface.The atomic force microscopy proved that SeTPS-1 and SeTPS-2were irregular coiled fibers,and SeTPS-2 was more aggregated than SeTPS-1.3.The hydroxyl radicals scavenging ability,ABTS radicals scavenging ability,reducing power and DNA damage protection activity of SeTPS-1 and SeTPS-2 were evaluated.The results found that SeTPS-1 and SeTPS-2 had good hydroxyl radicals scavenging ability,ABTS radicals scavenging ability and reducing power,and concentration-dependent in the concentration range.SeTPS-1 and SeTPS-2 also had a good protective effect on DNA damage induced by H₂O₂,which indicated that selenium polysaccharide had great development potential in the fields of medicine and food.