Abstract: In order to find out the effects of ultrasonic on the extraction and relative molecular weight of tea polysaccharide, the factors including temperature, material to liquid ratio, time, pH and ultrasonic power, which affect the extraction rate of tea polysaccharide were studied. The test was arrange by orthogonal design. The results showed that the optimum conditions of the traditional preparation method are: 60 ℃, 20:1 of the material to liquid ratio, 120 min, pH6.0; under these conditions, the extraction yield of tea polysaccharide is 4.26%. The optimum conditions of ultrasonic-assisted extraction are: 150 W, 30:1 of the material to liquid ratio, 40 min, 60 ℃, pH7.0, and the extraction yield of tea polysaccharide is 5.15%. Through the GPC determining, relative molecular weight of tea polysaccharide obtained from conventional extraction is 66439, and that of tea polysaccharide obtained from ultrasonic-assisted extraction is 47447. The results showed that ultrasonic-assisted extraction could increase the extraction yield of tea polysaccharide, but tea polysaccharide was depolymerized.

Key words: tea polysaccharide, ultrasonic-assisted extraction, orthogonal design, extraction, relative molecular weight