Comprehensive Extraction Technologies of Active Constituents of Tea

Using mid-grade and low grade green tea as raw material, the comprehensive technology of extracting tea-polyphenols, tea-polysaccharide and caffeine was studied. The effect of microwave treatment on tea-polyphenol leaching characteristics was probed and the technology of extracting tea-polyphenols, tea-polysaccharides, and caffeine from the same tea material was developed. The result demonstrated that microwave treatment could improve leaching active constituents of green tea. Using purified water as the solvent, being leached 2 times by microwave (material-water ratio 1∶20, time: 3 min), the green tea with an average size of 0.246 mm was leached by purified water (50℃) once in 10 minutes. The result showed that the leaching rate of tea polyphenols was 90.73%, which was higher than that of being leached by the mixture of ethyl alcohol and water. Using Al³⁺ to sediment tea-polyphenols, it was also revealed that the best range of pH was from 5.3 to 5.7. Using acid solution with pH1.5 to dissolve TP-Al 3+ (ratio between experimental solution and acid solution was 1∶2), the mixture of acid solution and TP-Al³⁺ was soaked in the water (50℃) for 15 minutes. The result showed that it was the best dissolved condition and the dissolved rate was 79.09%. The experiment combined the extractive method with the sublimational method to prepare caffeine, and the result showed that the production of caffeine was higher than that of direct sublimational preparation. It was also revealed that the experimental solution among which the concentration of NaCl was 0.2% was extracted 3 times by acetic ether whose volume was two times the experimental solution, the extraction rate was 95.14%. Using purified water as the solvent, leached by microwave treatment and water, separated by solvent extraction and sedimental extraction, tea powder could prepare tea-polyphenols about 11.8%, tea-polysaccharide about 1.5% and caffeine about 1.2%. This is remarkably superior to single solvent and sedimental extraction.