| Tea polyphenols are a natural antioxidant extracted from tea dust and coarse tea, that have a variety of effects like anti-aging, scavenging excess free radicals and slimming, and have been widely used in fields like food, pharmaceuticals, fine chemicals and so on. In recent years, several common methods have been reported to separate tea polyphenols, such as organic solvent extraction method, metal ion precipitation method and resin adsorption separation method. But the extraction and separation effect of the target product of these methods are not ideal. The removing of pectin, protein and other macromolecules from tea infusions applying membrane separation method, could not only reduce the pressure of the following purification, but also greatly reduce the amount of ethyl acetate needed and improve the quality and safety of product. Taking green tea dust and pure water as raw material and solvent, extraction of tea infusion was conducted. Then microfiltration-ultrafiltration membrane separation technology was used to extract tea polyphenols using membranes of different nominal molecular weight cut-off (MWCO) values, at different transmembrane pressure (TMP) and different temperatures. The effects on membrane flux, tea colour and rejection coefficient of active constituents in tea infusion were investigated. The suitable conditions of membrane separation were then concluded. After pectin, proteins and other macromolecules in tea infusion were removed, organic solvent extraction method was investigated for the separation and purification of tea polyphenols, and the suitable conditions of extraction with ethyl acetate were obtained. After a series of following experiments:concentration, back extraction and cryodesiccation, high-quality tea polyphenol product was obtained. Based on these experiments, a5t/a tea polyphenols production line was designed. The main research results are as follows:(1) Based on the single factor experiments, orthogonal test was conducted in studying the water extraction of tea polyphenols, the optimal process conditions were:tea dust granularity of30, extraction temperature90℃, extraction time20min, liquid-tea ratio25. Under these conditions, tea polyphenols extraction efficiency was25.95%after being extracted3times. (2) Tea infusion was purified by applying microfiltration-ultrafiltration membrane separation technology, and the results indicated that ultrafiltration effect of membranes with MWCO of30,50and100kDa were better than those of5kDa and8kDa. Taken membrane flux, tea colour and rejection coefficient of active constituents in tea infusion into consideration, the suitable condition of ultrafiltration were:polyethersulfone (PES) membrane of50kDa MWCO, at a trans-membrane of0.4MPa, and at temperature of25℃.(3) Extraction on ultrafiltration permeating liquid with ethyl acetate was investigated, and the proper extraction conditions were:ethyl acetate and tea infusion volume ratio1.2, extraction time80min with stirring at times. After a series of processes of extraction, concentration, back extraction and cryodesiccation were conducted on the permeated infusion, uniform loosely tea polyphenol powder products with yellowish color were achieved, with good solubility, high purity (higher than92%) and a higher yield (higher than7.6%).(4) The contents of tea polyphenol products were analyzed using HPLC, and the results were (mass ratio):polyphenol92.72±0.23%, total catechins68.24%, EGCG42.32±6.86%, EGC10.43±0.08%, ECG9.87±5.43%, EC5.62±0.14%, and caffeine0.98±0.10%. Among these contents, the content of EGCG, EGC content is highest, indicating that the extraction and purification of tea polyphenols could well keep its active components using membrane separation method.(5) A5t/a tea polyphenols production line were designed. The production technology is advanced, and calculation and selection of equipment and workshop equipment layout are presented. The design was feasible by accounting and economic benefits assessment. |
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