Study On The Enzymatic Extraction And Functional Properties Of Proteins From Tea Residue

Tea residue is a kind of by-product from the tea polyphenols processing industry, whichcontains20%to30%protein. The amino acid composition of tea protein is reasonable.However, the protein in tea residue has not been well exploited because it contains about80%glutelin and14%prolamin which is insoluble in water and has bad digestion and absorption,making it difficult to extract. The study on the protein from tea residue is still at the laboratorystage. The most of the tea residue protein is extracted by alkali method; the enzymatic methodwhich has low extraction yield, is rarely reported. The aim of this study was to improve theextraction yield of the enzymatic method; analysis the physics and chemistry characters andfunction properties of the protein extracted by enzymatic method compared with alkalimethod. At the same time, in order to provide a scientific basis for expanding tea residuerecycling, the tea residue was applied into the reconstituted tobacco after extracting protein.Firstly, alkali method and enzymatic method were comparatively studied in this paper.The result shows that:(1) the optimum extraction condition of the enzymatic method obtainedis as follows: tea residue were extracted at temperature50℃, the ratio of liquid to solid25:1,with1.5%cellulose and2.5%pectinase for2h, and for another1.5h at60℃and pH9.5with2.5%alcalase, under these conditions, the protein extraction yield was63.97%.(2) theoptimum extraction parameters of the alkali method were NaOH concentration0.1mol/L, theratio of liquid to solid (V/W)15:1, extraction temperature80℃, extracting time30min,particle size80mesh and extraction times3, through which the protein extraction yield was72.89%;Secondly, protein samples were obtained after the following treatments, namely, proteinprecipitating at isoelectric point, H2O2bleaching, remove of H2O2by hydrogen peroxidase,dialysis and freeze-dried. The purity, amino acid composition, nutritive value, the thermaldenaturation temperature and the functional properties of the tea protein extracted by alkalimethod and enzymatic method were comparatively analyzed. The results showed that thepurity were63.87%and60.24%respectively for the tea protein processed by alkalin andenzyme; amino acid composition is alike by the two methods and the score of ratio coefficientof amino acid (SRC) is68.53and73.19; the thermal denaturation temperature is103.36℃and130.70℃respectively; tea protein extracted by enzymatic method has higher nutritionalvalue, better solubility, emulsibility, and foamability, but foaming and emulsifying stabilitywere slightly weaker than that processed by alkalin.Finally, tea residue which has been extracted protein was added into the reconstitutedtobacco with different content, and then smoke components and sensory property wereanalyzed. The result showed that, when adding30%tea residue, the harm of nicotine and tarcan be reduced to a low level, and the suction quality is good. So it provides a novel thoughtto utilize tea residue after extracted protein.