Study On The Technology Of Decaffeination Of Tea

The caffeine in tea is functional to human body, however, intake of caffeine adversely affects the health of some caffeine-sensitive population. In order to meet these populations'needs of tea, the research of low-caffeine tea has significant benefits. In this paper, methods of vacuum sublimation, supercritical CO₂ extraction and polyphenols aqueous extraction were used to remove caffeine from tea. The effect and the final quality of the decaffeinated tea were studied. All these studies provide a reference for the manufacture of low-caffeine green tea.1. After green tea was pretreated, vacuum sublimation and supercritical CO₂ extraction were taken to remove caffeine from tea. The optimal process for the vacuum sublimation method was: infiltrates tea with two times its mass of water, deal the samples with co-extraction instrument of ultrasound-microwave and the parameters are microwave power of 300 W, ultrasonic power of 50 W, processing time 30 s, then vacuum sublimate at 90℃for 4 h, the tea caffeine removal rate reached to 62.24%. The optimal process for supercritical CO₂ extraction was: adjust moisture content of the tea sample to 55%, add 60 percent of the mass of tea samples of 95% ethanol as entrainer, extract under 70℃and 30 MPa for 2 h, the tea caffeine removal rate was 62.24%.2. Take tea polyphenols aqueous extraction treatment to remove caffeine from tea. The results showed that the optimum process parameters for the fresh tea leaves were: temperature of 95℃, solid to liquid ratio of 1:10 (W/V), the mass-volume fraction of polyphenols aqueous solution was 5% , processing time 5 min, the tea caffeine removal rate was 91.02%. The optimum process parameters for the dried tea leaves were:temperature of 95℃, solid to liquid ratio of 1:20 (W/V), the mass-volume fraction of polyphenols aqueous solution was 15% , processing time 7 min, the tea caffeine removal rate was 86.61%. Contrast with the traditional hot water extraction method, the polyphenols aqueous solution extraction, whether removal of caffeine and polyphenols on thereservations, have a distinct advantage The results showed a combination of tea polyphenols and caffeine, the combination was good for the removal of caffeine.3. The effect of caffeine removal by tea polyphenols aqueous solution extraction is obvious. In order to further improve this process to achieve the purpose of recycling, we use lignocellulose to remove the caffeine in the lixiviation solution after extraction by tea polyphenols aqueous solution. The results of static adsorption and analytical experimental showed that poplar and fir wood cellulose selection coefficient of tea polyphenols significantly higher than that of pine and camphor. Segment elution by distilled water and 60% ethanol makes the best separation effect of caffeine and tea polyphenol. Take poplar lignocellulose for dynamic elution experiment, the results showed that the separation effect of caffeine and polyphenols was good. Analyze the eluate by HPLC, the results showed that ester type catechins can separatied with caffeine easier compared with non-ester catechins. These indicated that poplar lignocellulose had great potential for applications in the separation of caffeine and enrichment of ester-type catechins in tea polyphenols. The decaffeinated tea polyphenols were used to decaffeinate the fresh tea by the method of tea polyphenols aqueous solution extraction,the caffeine removal rate is 89.98%.4. Caffeine removal rate was the main indicator of the process of low-caffeine tea manufacturer, and the impact of the treatment processes on other qualities of tea samples were ignored. In this paper, we take a comprehensive evaluation among the impacts of the three processes on the qualities of tea. The results showed that:(1) Extraction process by polyphenols aqueous solution makes the best effect of decaffeination, the tea caffeine content was less than 5 mg/g, and the polyphenol content increased,the content of water extracts,total free amino acid,tea polysaccharide loss less than 13%. The caffeine content in tea samples treated by vacuum sublimation and supercritical CO₂ extraction process was about 10 mg/g, and the loss of tea polyphenol, water extracts, tea polysaccharide was more than 12%. (2) Compared to fresh tea treated by extraction of supercritical CO₂ and extraction of polyphenols aqueous solution, the surface structure of dried tea treated by vacuum sublimation and polyphenols aqueous solution extraction change significantly, which affected the appearance of tea and its resistance to foaming. (3) There exist some loss of volatile components of tea in the three methods mentioned above. The vacuum sublimation processing made the biggest loss of volatile components.The Relatively alcohols and aldehydes loss of dried tea treated by supercritical CO₂ extraction and polyphenols aqueous solution extraction was 24.76% and 13.62% compared to untreated tea. Least change of volatile components was shown in the fresh tea treated by polyphenols aqueous solution extraction while compared with the original tea. After adding flavor back to the decaffeinated tea, the relative content of characteristic volatile components have increased.(4) In summary, tea polyphenol solution extraction of fresh tea processing was the best technology for manufacturing the low-caffeine tea.