Study On The Extraction Of Dietary Fiber From Tea Residue And Its Modification As Dye Adsorbent

In this paper, insoluble dietary fiber (IDF) was extracted from tea residue by chemical method. Single factor and orthogonal experiments were carried out to determine the optimal conditions and the characteristics of IDF were studied.The optimal processing conditions for extracting tea IDF by chemical method were:1%NaOH concentration,1:20ratio of material/solution,50℃,1h extraction time. The yield of IDF reached38.56%under these conditions.The extracted IDF showed high adsorption ability to water and fat. The water holding capacity reached1.31g/g with3.67mL/g swollen volume and the adsorption capacity for lard and peanut oil reached1.31g/g and0.89g/g respectively. The results also showed that the tea IDF had strong binding capacity (about3.336μmol/50mg) of three bile salts indicating that tea IDF has good effect in lipid-lowering.On the other hand, modification on black tea and green tea residue were carried out through etherification and amination.Experiments on adsorption of the modified tea residue for Direct Red4B, Reactive Dark Blue B and Vat Yellow G involving contact time, initial dye concentration, pH and temperature. Meanwhile, the adsorption mechanistic of modified tea residue were studied via kinetics and equilibrium isotherms and FTIR spectrum and SEMThe results showed that the adsorption ability of the modified tea residue against Direct Red4B, Reactive Dark Blue B and Vat Yellow G exhibited much higher than the unmodified material. The dye removal efficiencies for Direct Red4B, Reactive Dark Blue B and Vat Yellow G by coagulation were more than80%within60minutes. Direct Red4B was found easier to be removed followed by Reactive Dark Blue B and Vat Yellow G from waste water. The adsorption ability of the the modified tea residue against the three dyes depends on various experimental parameters such as contact time, initial dye concentration, pH and temperature. The modified tea residue showed the higher ability at the range of pH(4-8), temperature (40-50℃), contact time(60-120min),and initial concentration (100-200mg/L).It was found that the experimental data fitted well to the pseudo-second order kinetics model for three dyes. Reactions between the modified tea residue and dyes could be well described by Longmuir adsorption isotherm and Freundilich adsorption isotherm, with their correlation coefficient r all higher than0.9. FT-IR analysis indicated that the epoxidation and amination reactions took place on the tea residual. SEM analysis showed that the surface change of green tea residual, suggesting the chemical modification.