Extraction, Characteirzation And Applied Research Fhemicelluloses Of Green Tea-residue

Leafy residue from the commercial production of beverages from green tea is presently alow-value waste. Due to the rapid growth of the tea-based beverage industry, higher-valueuses of the residue would be advantageous. This study lays a theoretical foundation for thosepossibilities by determining the optimal conditions for hemicellulose extraction from greentea-residue and characterizing the products. The application of hemicellulose extracts for thepreservation of sliced, fresh apple is also described.The optimal conditions for extraction of green tea-residue hemicelluloses by alkalinehydrogen peroxide were determined by comparing the effects of liquid-solid ratio, time,temperature and the concentrations of sodium hydroxide and hydrogen peroxide on thecontent of total sugar and free monosaccharide. Temperature and sodium hydroxideconcentration significantly affected the extraction. The optimum yield of hemicelluloses(34.6%) was obtained under the following conditions: liquid-solid ratio30(v/w), time2h,temperature70oC, sodium hydroxide0.75%and hydrogen peroxide3%. The total sugarcontent was34.5%±0.5%. The green tea-residue hemicelluloses content a few protein andpolyphenols and lots of uronic acid. Fourier-transform infrared (FT-IR) spectra of thehemicellulose extracts revealed typically characterization of hemicelluloses.The hemicelluloses were separated into five sub fractions by precipitation in seriallyconcentrated ethanol, viz.0%,20%,40%,60%, and80%(v/v). And the sub fractions werenamed as H0, H20, H40, H60, H80respectively. The five sub fractions had similar sugarcomposition; the main sugars being galactose, arabinose and glucose. H60and H80hadrelatively low contents of galacturonic acid. FT-IR spectra showed that H0, H20and H40havemore significant characteristic of hemicelluloses. All the hemicelluloses were significantlydegraded by temperature in the range from199oC to390oC, but H60and H80were mostthermally stable.The effect of exchange resins on the purification of water-soluble hemicelluloses fromgreen tea-residue was also evaluated. Anion exchange resin D280provided high de-colorationability. The de-coloration ratio of green tea-leaf hemicelluloses was72.6%, yield was42.6%ubder the conditions for de-coloration by D280were determined by static absorption at25oC,pH6. Dynamic absorption using a2mg/mL sample solution (pH6.5~7.5, temperature25oC,volume15~20%) yielded one neutral polysaccharide after elution with water. An acidicpolysaccharide was obtained with0.1mol/L NaCl elution. The effect of coatings of green tea-residue water-soluble hemicellulose in combinationwith potassium sorbate and chitosan (1%,1%and0.5%respectively) on the preservation offresh apple slices during cold storage was evaluated. Coating treatment effectively retardedenzymatic browning and maintained firmness and weight of apple slices compared withdistilled water. The results indicate that coating in water soluble hemicelluloses from greentea-residue, in combination with potassium sorbate and chitosan, is a promising way toextend the shelf-life of apple slices.