Basic Research On The Application Of Functional Polymers In Tea Comprehensive Processing

Global consumption of caffeine has been estimated at 120000 tons per annum, 20%～25% of it is used in industry and the rest of it is used in food and medicine. In recent yeas, the synthetic caffeine is prohibited in the fields of food and drink in most of developed countries due to its harm on human health and environment. It brings limitless business opportunity to natural caffeine. In foreign countries, natural caffeine is mainly from the by-product which is produced during the processing of coffee. Our country is the biggest tea manufacturing country in the world, and is rich in all kinds of tea wastes which are produced during the manufacturing of tea. Therefore, extra-cting caffeine from the tea wastes features the advantages of ready availability of raw material and simplicity of procedure. But the cost of natural caffeine extracted from tea or coffee is much higher than that of the synthetic caffeine, which limits the pro-duction and application of natural caffeine in large scope. So it is necessary to lower the cost of natural caffeine. Microbial fermentation was applied in the paper to increase the caffeine content in tea, which would decrease the cost of natural caffeine. The results demonstrated that the microbial fermentation did increase the caffeine content of tea. The analysis of microorganisms and caffeine showed that the fungi and yeast had effects on the change of caffeine content, while the bacteria had no effect on the change of caffeine. The single microorganism was further used in the fermentation of black and green teas in order to find which microorganism has the biggest effect on the caffeine content increase. The results illustrated that the three molds applied in this study could enhance the caffeine content in green tea through fermentation, whereas the two yeasts had no this effect. Among the three moulds, Aspergillus niger van Tiegh em had the most positive effect on the increase of caffeine content. On the 16th day of fermentation with Aspergillus niger van Tieghem, the caffeine content reachs a maximum value of 9.63%. In comparison with an initial 3.47% in starting tea, the caffeine content increased by 177.5%. A conclusion can be drawn from the compre hensive analysis of the results: The microorganisms are stimulated to establish a new secondary metabolism route to biosynthesize caffeine in vivo after taking up the essential and especial components such as xanthosine from teas. These components are poorly soluble in water and the contents of them in black tea are much lower than that in green tea. The biosynthesis of caffeine in the microbial metabolism may be via the methylation of the theophylline, while the biosynthetic route of caffeine in the tea plant is via methylation of theobromine.However, more residue of caffeine in tea polyphenols has a negative influence on the application of tea polyphenols in some fields. So it is necessary to reduce the caffeine content in tea polyphenols. Now, the common method for the removal of caffeine from tea polphynols is the extraction by chloroform. The Supercritical carbon dioxide is also used for extraction of caffeine. Although they are effective in the removal of caffeine, there are many problems in these two methods such as the residue and harm of organic solvent and the big one-off investment of the equipments for supercritical carbon dioxide extraction of caffeine. Therefore, somebody separates caffeine from tea polyphenols with column chromatography and makes achievements. The C₁₈ column and Gel column and High-speed countercurrent chromatography are used for the separation of tea polyphenols and caffeine. But the costs of C₁₈ and gel column are high, while the High-speed countercurrent chromatography cannot reach a preparation scale. So it is important for us to find a kind of suitable and cheap solid phase for the separation. According to the relevant research, a molecularly imprinted polymer(MIP) is prepared with caffeine as the template molecule by the molecularly imprinting technique in the paper to separate caffeine from tea polyphenols with the selectivity of molecular weight and structure. The results indicate that the preparation of MIP using methacrylic acid(MAA) as the functional monomer, caffeine as the template is perfect by aqueous micro-suspension polymerization. The best ratio of template to functional monomer is 1:12, methanol to acetic acid to water as mobile phase. The results demonstrate that the MIP with caffeine as the template can separate caffeine from tea polphenols, the separation degree of caffeine and epigallocatechin gallate(EGCG) is 2.39. Of course the separation by MIP leads to the loss of some components of tea polyphenols.Epigallocatechin gallate(EGCG) which is the dominant component of catechins is gotten attention from all circles because of its stronger pharmacological function. The sephadex gels are used in the common method for preparation of EGCG. The high-speed countercurrent chromatography is also adopted to prepare EGCG. In addition, these two methods are combined into the procedure of preparing EGCG. All of them make good results. But the preparation scale is small and the cost is very high. In this paper, a molecularly imprinted polymer(MIP) was prepared with EGCG as the template molecule by the molecularly imprinting technique to separate EGCG from tea polyphenols. The results indicate that the preparation of MIP using 4-vinylpyridine as the functional monomer, EGCG as the template is perfect by aqueous microsuspension polymerization. The best ratio of template to functional monomer is 1:16. The results demonstrate that the MIP of EGCG can realize the chiral separation of enantiomers, the separation degree of EGCG and GCG is 1.52. The separation degree of EGCG and epicatechin gallate(ECG) on the MIP of EGCG is only 0.60 because they have more similar structure. The separation degree of caffeine and EGCG is 2.30. The result of separation of tea polyphenols with MIP of EGCG indicates that the preparation of EGCG through the MIP column is reliable.Tea pigments which include theaflavins, thearubigins and theabrownin are the oxidation products of catechins. They have good effects on cardiovascular diseases and tumor. The pigments could be obtained by two ways: oxidation of catechins by the catalysis of polyphenol oxidase and peroxidase or by the chemical oxidant such as potassium hexacyanoferrate(â…¢). Although polyphenol oxidase and peroxidase have the specific oxidative ability for catechins, the cost of enzymatic reaction is very high because it is difficult to get and reuse the enzymes. Artificial enzyme mimics which not only have the ability of enzymatic catalysis but also have more stability than natureal enzymes could be prepared in batch. The enzyme mimics don't dissolve in water and organic solvent, which is convenient for its recovery. In this paper, low-molecular weight chitosan was used to synthesize the chitosan schiff base via the reaction of chitosan with salicylaldehyde. And then chitosan schiff base copper complex was obtained by reaction of chitosan schiff base with copper(â…¡) salt. Crosslinked chitosan schiff base copper complex was prepared using epichlorohydrin(ECH) as cross linker. The results indicates that the copper complex has the same but low catalytic property as horseradish peroxidase, only 28.28% of the activity of horseradish peroxidase using pyrogallic acid as substrate. But the copper complex can be used again after filtration from the reaction system. The experimental data show that the activity of enzyme mimic(chitosan schiff base copper complex) decrease little and is 86.18% of the activity of the first time after four repeat. The loss of activity may be caused by the crush of enzyme mimic during the stirring and the adsorption of catechins by enzyme mimic. However, it is no problem for chitosan schiff base copper complex using as the mimetic enzyme of horseradish peroxidase to catalyze the oxidation of catechins to form theaflavins and thearubigins.The other method for preparation of tea pigments is through the oxidation of catechins by chemical oxidants. The common oxidant is potassium hexacyanoferrate(â…¢) which can yield more products. But it is difficult to recover it from the reaction system, which is not good for the timely stop of oxidation reaction and the safety of product. Meanwhile, the using of potassium hexacyanoferrate(â…¢) which can produce hydrocyanic acid after being treated with acids may harm the environment and the body. And then the potassium ferrocyanide which is the reduction product of potassium hexacyanoferrate(â…¢) also produce virulent hydrocyanic acid when meeting the acids or acidic salts especially at high temperature. In order to increase the stability of potassium hexacyanoferrate(â…¢) and reduce the harm of it and realize the complete separation from the product, the ion-exchange resin is used to adsorb ferricyanide by exchange and then to oxidize the catechins to form tea pigments. The results demonstrated that the theaflavins could be prepared by the oxidation of catechins using the ferricyanide supported by 717 strong base anion exchange resin as oxidant. The activity of polymer-supported oxidizer is much lower than the free potassium hexacyanoferrate(â…¢). The peak area of main product by oxidation of DL-C and EGCG using polymer-supported oxidizer is 510351.9,49.71% relative to the peak area of the same product using free potassium hexacyanoferrate(â…¢) as oxidizer. The resin-supported oxidizer will be regenerated by oxidation of it with H₂O₂, which must be helpful for us to reduce the production cost and reduce the environmental pollution.