| The chemical ingredient of tea is very complex and variety. These ingredient comprises the following main components:tea polyphenols, tea polysaccharides, amino acids, vitamins, caffeine, flavonoids and a variety of minerals, etc. Among them, tea polyphenols contains many active hydroxyl groups that have a very strong antioxidant, can clear reactive oxygen species, inhibit lipid peroxide. In addition, tea polyphenols also has various pharmacological activities with bacteriostasis and bactericidal, anti-aging, anti-radiation. And it is a new type of natural antioxidant. The tea polyphenols already has been widely used in food, medicine, daily-use cosmetic and other fields. The flavonoids is a product of photosynthesis that can not be synthesized in the human body and can only be obtained from food or medicines. Many health functions relating to the flavonoids can effect during drinking tea, such as falling blood pressure and anti-tumor.Many tea products were developed in recent years, such as tea health products, food containing tea powder, tea cosmetics. But tea resource utilization is still very low in our country, especially the scraps from the utilization in tea and the low value tea. Therefore, the extraction and separation technology will be the focus of attention with efficient, cheap, green tea and suitable for industrial production.The extraction methods of tea polyphenols and flavonoids include solvent extraction, precipitation method, ultrasonic method, microwave method, enzyme hydrolysis and supercritical extraction method and so on. But these extraction method have their respective advantages and disadvantages. Most of them can only be carried out under the laboratory conditions and consume more resources. They will not only pollute the environment, but also endanger the health of people because the organic solvent or heavy metals was used inevitably in the process of extraction. In recent years, the mechanochemistry is used more and more widely in the extraction process of active ingredients in plant. This method can not only improve the extraction rate of active ingredients, but also realize to extract some water-insoluble organic matter using water. Therefor, it will have a good application prospect.The mechanochemistry includes both superfine grinding and solid state chemical reaction. The superfine grinding breaks plant cell wall to increases the particle surface area and to exposes the effective component, then to form fresh slice in the material surface. The solid state chemical additives reacts with the active substance in the fresh slice. Thus the effective component is modified, Thereby the dissolution characteristics of the effective component is changed. Hence, the dissolution rate of these components in the particular solvent is improved.It was focused on the mechanochemical assisted extraction of tea polyphenols and total flavonoids from waste tea dust with water as solvent in present study. The method simplifies the extraction process, reduces energy consumption and production cost, improves the utilization rate of tea raw materials, and puts forward a new way taking advantage of high-value tea byproducts.The main contents of this study include 4 parts. First, the best additive was selected according to the yield of target compounds by the mechanochemical method. Then, the influence of each single factor on the yield of extracts was investigated. Secondly, the process was optimized based on both one-factor experiment and response surface analysis. Finally, the mechanochemical method was compared with conventional heat reflux extraction and superfine grinding extraction method. These results showed that: (1) Na2CO3 & Na2B4O7 and β-cyclodextrin are the best extraction adjuvants in the process of he mechanochemical assisted extraction of tea polyphenols and total flavonoids from waste tea dust. The mass ratio of Na2CO3 & Na2B4O7 is 1:2. The Na2B4O7 is to protect the molecular structure. (2) The Na2CO3 & Na2B4O7 as extraction adjuvant, the each single factors experiment was carried which effect of alkali adjuvant content, ethanol concentration, material-to-solvent ratio and extraction times, extraction temperature and solution pH on the extraction efficiency of tea polyphenols and total flavonoids. The effect of alkali adjuvant content, ethanol concentration and solid-to-solvent ratio and extraction time on the extraction efficiency of tea polyphenols and total flavonoids were investigated by the Box-Behnken experiment design principle and the response surface analysis. A quadratic polynomial model was established and validated to be highly significant and allow the prediction of the extraction efficiency of tea polyphenols and total flavonoids. The optimum condition for the extraction of total flavonoids is 40% ethanol as the extraction solvent at a solid-to-solvent ratio of 1g/53mL, alkali agent content of 6.3%, pH of 4.0,50℃ and extracting 3 times. The extraction efficiency of total flavonoids is 9.08% under the optimum condition. The optimum condition for the extraction of tea polyphenols is 32% ethanol as the extraction solvent at a solid-to-solvent ratio of 1g/52mL, alkali agent content of 6.0%, pH of 4.0,50℃ and extracting 3 times. The extraction efficiency of tea polyphenols was 28.98% under the optimum condition. (3)The tea polyphenols and total flavonoids was extracted from tea dust with P-CD as extraction adjuvant and distilled water as extraction agent. Based on the single factor experiment, the effect of β-CD content, extraction temperature and material-to-solvent ratio on the extraction efficiency;of tea polyphenols and total flavonoids were investigated by the Box-Behnken experiment design principle and the response surface analysis. A quadratic polynomial model was established and validated to be highly significant and allow the prediction of the extraction efficiency of tea polyphenols and total flavonoids. The optimum condition for the extraction of tea polyphenols is β-CD content of 8.41%, extraction temperature of 58℃, solid-to-solvent ratio of 1g/57mL. The extraction efficiency of tea polyphenols is 27.96% which is close to the predicted value of 28.06% under the optimum condition. The optimum condition for the extraction of total flavonoids is β-CD content of 8.27%, extraction temperature of 53℃, solid-to-solvent ratio of 1g/61.83mL. The extraction efficiency of total flavonoids is 7.843% which is close to the predicted value of 7.835% under the optimum condition. (4) The mechanochemical assisted extraction compares with conventional heat reflux extraction and superfine grinding extraction method, the results showed that:①In the process of extracting total flavonoids, the yield of total flavonoids with 40% ethanol and alkali agent content of 6.3% assisted extraction reachs the highest and is up to 9.08%. The yield of total flavonoids by reflux extraction method with distilled is the lowest and only reached 7.635%. The extraction efficiencies of total flavonoids are up to 8.902% and 7.858% with the solvent 20% ethanol and distilled water as extraction agent under this condition, respectively. Comprehensive comparison, the extraction efficiency of total flavonoids increase less than 1.3% with alcohol than water as extraction agent.②In the process of extracting tea polyphenols, the yield of tea polyphenols with 32% ethanol and alkali agent content of 6.0% assisted extraction reachs the highest, and is up to 28.98%; and the yield of tea polyphenols with β-CD assisted extraction is also relatively high and reachs 27.96. The yield of tea polyphenols by reflux extraction method with distilled water is the lowest and only is 25.98%.Therefore, the mechanochemical assisted extraction has less time, more saving energy, higher extraction efficiency, more industrial production advantage in the actual production from the raw material costs and the sustainable development. |
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