| In China, tea is one of the most traditional drinks with a long history; Chinese people have a long-standing habit of drinking tea. Tea not only has a nutritional value, but also has medicinal value. It is recorded by many historical medical books that tea has more than20functions including thirst diuretic, refreshing, helping digestion, promoting urination, relieving asthma, eliminating phlegm, improving eyesight, decreasing inflammation and prolonging one's life. In recent years, a number of studies have suggested that tea also has the effects of reducing weight, reducing blood pressure, benefiting heart, enriching the blood, resisting arteriosclerosis, decreasing blood sugar, anti-cancer, reduce radiation damage et al. Selenium is one of the essential trace elements in human body. Tea tree is the crop plant which has the capability of concentrating selenium and can transform the absorbed inorganic selenium into organic selenium. Natural selenium-enriched tea can be used as a way of easy, affordable and enriching selenium without any side-effect, while domestic and overseas pay little attention to natural selenium-enriched tea studies. With the rapid increase of deep-processed products such as the tea beverage, instant tea and tea polyphenols, it produces a large number of tea-leaf. However, nowadays, the research of recycling of tea-leaf in our country is still in the initial stage.Therefore, the aim of the study is that exploring new resources for supplying selenium and the way of more effective fully utilized of tea, avoiding environmental pollution of the tea-leaf, and increasing economic efficiency. The main contents and results of this paper are as follows:1. The study of combined forms of selenium in tea from Ziyang County.The determinations of combined forms and contents of selenium are mainly through the study of the contents of it in tea polyphenols, tea protein and tea polysaccharide. The determination of contents of selenium is through hydride generation atomic fluorescence spectrometry (HG-AFS). The results show that the ratio of selenium in tea polyphenols is0.89%in total selenium content; the ratio of the selenium in tea protein and in tea polysaccharide is60.12%and18.06%respectively. Meanwhile, Alkali-soluble protein seems to contain the highest amount of bound selenium, contributing to23.81%of total selenium content. It shows that tea leaves of selenium-rich tea contains more selenium after bubble drink or extracting tea polyphenols, which can be used in the preparation of selenium-rich tea protein and polysaccharide, also can be considered to add to food or feed in certain proportion in order to increase the intake of organic selenium, plant protein and dietary fiber.2. The development and utilization of tea residuesThis part mainly uses orthogonal test to study the extraction technology of tea polysaccharide and tea protein from tea-leaf and predicate the alkali soluble protein from selenium-rich protein.(1) Optimization of extraction condition of tea polysaccharide from tea residues.Tea-leaf is made after extracting tea polyphenols from low-grade tea. Study the water extraction and preliminary purification technology of tea polysaccharide. Main factors of extraction technology such as material-to-liquid ratio, extraction time, extraction temperature, and number of extraction times are researched through single-factor experiments. The optimum extraction technology is confirmed through orthogonal test of L9(34). The preliminary purification technologies of alcohol precipitation and taking off protein on tea polysaccharide are investigated. The optimal conditions are as follows:the ratio of material to liquid is1:30, extraction temperature is85℃, extraction time is2hours for three times, ratio of concentrated solution to95%alcohol is1:5, alcohol quiescence time is6hours, and the protein is removed with Sevage method by3times, the final polysaccharide yield is4.10%.The structure of tea polysaccharide is observed by atomic force microscope (AFM) and environmental scanning electron microscope (ESEM). And the antioxidant activity of tea polysaccharide is measured in chemical simulation system in vitro. The ultraviolet-visible (Uv-vis) spectrum of tea polysaccharide showed that the Sevage method is not able to remove all protein. It is possible that part of the protein in the tea covalently combines saccharides to form glycopeptide or glycoprotein. Through infrared spectroscopy analysis, saccharide ring in tea polysaccharide is furan ring. Morphological features of powder of tea polysaccharide from ESEM exist in three aggregation state. It is found that tea polysaccharide on mica shaped Multi-lateral branch-like structure by AFM. The results of tea polysaccharide in vivo oxidation shows that tea polysaccharide can scavenge DPPH·, and·OH, which has strong antioxidant capacity.(2) Optimization of extraction condition of alkali-soluble tea protein from tea residues.Extracting method by alkali solution is studied. Main factors of extraction technology such as material-to-liquid ratio, extraction time, extraction temperature, and concentration of alkali liquor are researched through single-factor experiments. The optimum extraction technology is confirmed through orthogonal test of L9(34). The optimal conditions are as follows:the ratio of material to liquid is1:50, extraction temperature is60℃, extraction time is18hours, and concentration of alkali liquor is0.1mol/L. Under these conditions, the final extraction rate of tea protein is4.10%. Through the comparison of acetone precipitation, ethanol precipitation and isoelectric precipitation, precipitating alkali soluble protein by isoelectric precipitation with the pH value of4are selected eventually, and the precipitation rate is89.76%.The ESEM and AFM are used to observe structure of tea protein. The result shows that: morphological features of powder of alkali-soluble tea protein from ESEM are in globular structures of regular shape and uniform size. Morphological features from AMF are in rod-like or globular structures of uniform size:the thickness is1.08nm, width is44.23-46.98nm for globular structures; the length is119.39-132.75nm, width is42.89-43.95nm, thickness is0.94-1.23nm for rod-like structures, and the surface of globular structure protein is smooth, rod-like structure is rough. Combining observation results of ESEM and AFM, we can assume that a rod-like structure is probably formed by two to three globular structures.(3) Separation and purification of selenium-rich protein from alkali soluble proteinThis part mainly uses the anion exchange chromatography and gel filtration chromatography to purify alkali soluble protein, testing the selenium by HG-AFS. The results show that:the alkali soluble protein tea get five protein elution peaks by ion exchange chromatography,the content of selenium in tea protein of the three fractions Peakl, Peak2and Peak5fractions is103.35ug/g,67.86μg/g and220.65μg/g respectively, and the three components of peak are performing in single one by gel filtration chromatography, which prove that the tea protein of natural selenium-rich tea contains plentiful organic selenium. |
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