Study On Extraction, Decoloration And Modification Of Protein From Tea Residue

The production of tea products such as polyphenols, instant tea and other tea related productsis accompanied by generation of large volumes of tea residues in china every year. These tealeaves still contain a variety of active ingredients, among them, the proportion of protein is up toabout20%. The study was therefore initiated to investigate parameters affecting the preparationsof tea protein concentrates. The treatment of tea at high temperature and moisture leads tochanges in the structure of tea making it hard to extract the protein from tea residue. Therefore,identification of appropriate extraction method is the main concern of preparing tea protein. Inorder to identify a suitable for effective extraction of the proteins from the tea residues, extractiontechniques including alkali, and ultrasound-assisted methods were investigated. Hydrogenperoxide was used to decolor tea protein, and was found to be simple and effective. After that, teaprotein was limited enzymatic hydrolyzed (Alcalase) through enzymatic modification technics, toprepare modified tea protein with low DH.Improved dissolution properties of tea protein.And thendetermine the functional properties of the tea protein.For the alkali method, the optimum meal (solid) solvent (water) ratio, alkali concentrations,temperature, and extraction time were1:40(w/v),0.5mol/L,90℃and120min, respectively, withextraction rate to be49.3%. In the case of the alkali altrasound-assisted extraction, responsesurface methodlogy was used to optimum extraction parameters. Results showed that theoptimum extraction condition were ultrasonic power of300W, frequency26kHz, temperature54℃，time61min, alkali concentration0.35mol/L and material-liquid ratio1g:27mL.Under theseconditions, the extraction rate of tea protein was86.5%.Activated carbon, ion exchange resion and hydrogen peroxide were used for decoloration oftea protein concentrates. The result showed tea protein treated with4%hydrogen peroxide for60min at25℃had high decoloration effect. Chroma and chromatism of tea protein afterdecoloration were L*45.83，a*-1.83，b*16.1.Analysis of the extracted products by gel-filtration chromatography and amino acid amylasemethod, showed as follows: tea protein was composed of two submits with molecular mass of1.26×106and2.4×104; tea protein has a favorable balance amino acid, which contains eight kindsof essential amino acids. glutamic acid, aspartic acid and leucine content are respectively reached12.27%,9.24%and10.22%, cysteine content was only0.09%, is the first limiting amino acid.Alcalase was chosen as hydrolase to limited hydrolysis tea protein. The correspondinghydrolysis parameter of Alcalase was that pH7.0, temperature25℃, substrate concentration10%and enzyme addition500U/g. The solubility of modified tea protein was increased distinctly.After enzymatic modification, tea protein has good emulsifying properties and excellentemulsion stability. Foam stability significantly affected by pH, at pH7tea protein has the best foam stability, when the pH is lower than3, although tea protein has a certain degree of foamingbut foam stability is very poor. The best tea protein concentrations for foaming is4mg/mL, morethan4mg/mL, foam ability decreased; when the concentration was2mg/mL,tea protein has thebest bubble stability. The foaming property of tea protein is relatively low, but has good bubblestability.