Methods for preparing high-hydrophilcity macroporous absorption resin and removing caffeine in crude tea extracts

Abstract

The invention discloses preparation of high-hydrophilcity macroporous absorption resin and a method for removing caffeine in crude tea extracts. A method for preparing the resin comprises the steps of: dissolving gelatin or polyvinyl alcohol in water to prepare an aqueous phase, mixing TAIC (triallyl isocyanurate) and VAc to form a polymeric monomer, adding long-chain aliphatic paraffins of C7-C12 as a porogenic agent and adding AIBN (azo-bis-isobutyronitrile) as an initiator to form an oil phase for polymerization; mixing the aqueous phase with the oil phase, stirring and heating, filtering out resin, washing the resin with deionized water and drying; and mixing the dried resin with a sodium hydroxide aqueous solution, stirring and heating for reaction, standing for cooling to room temperature after the reaction to prepare the high-hydrophilcity macroporous absorption resin. By using the high-hydrophilcity macroporous absorption resin for separating commercial crude tea extracts, thecaffeine in the crude tea extracts can be completely eliminated only through a simple continuous process including adsorption and elution in one step, and the yield of tea polyphenol is more than 90%. The process for removing the caffeine is simple to operate and is free from the application of toxic solvents, the resin is recyclable, the production cost is low, and the method is particularly suitable for large-scale industrial production.

Description

technical field [0001] The present invention relates to a synthesis method of a new type of highly hydrophilic alcohol hydroxyl macroporous adsorption resin and a process for removing caffeine in tea crude extract, especially under the premise of ensuring high recovery rate of effective components of tea polyphenols, A new method for preparing caffeine-free high-purity tea polyphenol extracts only through the one-step continuous process of "adsorption-elution" of resin. Background technique [0002] Tea is a rich natural plant resource in my country, and tea drinking and tea culture have a history of thousands of years. The main physiologically active substances in tea are divided into two categories, namely tea polyphenols and caffeine. Among them, tea polyphenols (Tea-polyphenols, abbreviated as TP) is a class of polyphenolic compounds mainly composed of catechins, accounting for about 20% to 33% of the dry weight of tea leaves, mainly including catechins (C). Catechin (...

AI Technical Summary

Problems solved by technology

Referring to the above molecular structure characteristics of tea polyphenols and caffeine, people introduce functional groups capable of forming hydrogen bonds into the resin skeleton. Compared with caffeine, tea polyphenols can form stronger hydrogen bonds with the resin. The role of the resin greatly improves the adsorption selectivity of tea polyphenols and caffeine. For example, Ye Jianhui et al. used polyamide materials to remove caffeine in tea polyphenols (Ye J H, Wang L X, Chen H, et al. Preparation of tea catechins using polyamide[J]. Journal of Bioscience and Bioengineering, 2010, In Press, Corrected Proof.), achieved good results, but polyamide materials are mostly amorphous and can only be used as column chromatography packing materials, and the separation is based on The number of theoretical plates of the chromatographic column is increased, so the processing capacity is low and the operation is complicated, often requiring external pressure, and the separation process cannot be completed at normal pressure

For this reason, functional groups such as amides and amine groups have been introduced into the backbone of polystyrene and polyacrylate resins through functional group reactions ([1] Lu J L, Wu M Y, Yang X L, et al. Decaffeination of tea extracts by using poly (acrylamide-co-ethylene glycol dimethylacrylate) as adsorbent[J]. Journal of Food Engineering, 2010, 97(4): 555-562. [2]Huang J H, Huang K L, Liu S Q, et al. Adsorption properties of tea polyphenols onto three polymeric adsorbents with amide group[J]. Journal of Colloid and Interface Science, 2007, 315 (2): 407-414.), which improves the adsorption capacity of tea polyphenols, but due to the strong resin skeleton Hydrophobic, so that the resin can still adsorb part of caffeine by hydrophobic effect, and can not achieve complete separation of tea polyphenols and caffeine

Based on the above considerations, people purposely reduced the hydrophobicity of the resin, such as synthesizing a weakly hydrophobic N-vinylpyrrolidone copolymer, which effectively avoided the non-specific effect of hydrophobicity on the resin adsorption selectivity. Tea polyphenols and caffeine were separated (Zhao R Y, Yan Y, Li M X, et al. Selective adsorption of tea polyphenols from aqueous solution of the mixture with caffeine on macroporous crosslinked poly(N-vinyl-2-pyrrolidinone)[J] . Reactive & Functional Polymers, 2008, 68(3): 768–774), but due to the strong polarity of N-vinylpyrrolidone, the difference in reactivity ratio with the cross-linking agent triallyl isocyanurate (TAIC) is relatively large Large, it is difficult to form a uniform cross-linking structure, resulting in low adsorption capacity of the resin, and it is difficult to meet the needs of large-scale industrial production. On the other hand, it is difficult to reduce the amount of hydrophobic cross-linking agent due to the limitation of the comonomer structure. To achieve the purpose of reducing the hydrophobicity of the resin, so the hydrophobic adsorption of the resin cannot be completely avoided, and part of the caffeine is still adsorbed by the resin, so that the final purified product still contains 2% caffeine, and solvent extraction, ion precipitation, etc. are still required The purpose of completely removing caffeine can only be achieved with the assistance of other methods, which will inevitably lead to the increase of removal cost and the complexity of process operation, and at the same time, it does not avoid the defects of solvent extraction, ion precipitation and other methods

Images