Formation Characteristic, Structure, Hypoglycemic Activity And Its Mechanism Of Polysaccharides From Oolong Tea

On the basis of experiment, it has turned out that Oolong tea polysaccharides had remarkable hypoglycemic effect for diabetic mice induced with streptozotocin or alloxan. In this paper, the biologic diversity and the formation characteristic of Oolong tea polysaccharide were investigated. The mechanisms on hypoglycemic activity of tea polysaccharides were also studied here .The main results were shown as follows:1.Conditions and parameters for extraction of tea polysaccharides.The influence of temperature, heating time, ratio of tea to water and pH value on extraction rate and activities of Oolong tea, Green tea and Black tea polysaccharides(TPS) were studied . The results showed that extraction rate of TPS was noticeably affected by pH, temperature, heating time and ratio of tea to water in significant order. It was concluded that pH was the main factor affecting activity of TPS, since activity of TPS extracted on the condition of acidity or alkalinity was very low. The model of extraction rate (Y) showed no significant lack of suitability at 5%, but it was statistically significant at 1%. The model was appropriate to express response variables. Considering high extraction rate and activity of TPS, the extracting conditions were optimized by using expectant function approach for simultaneous optimization of several variables levels, these were 0-1 temperature, 0~1 heating time, 0-0.5 ratio of tea to water and -0.95 pH.2.BioIogic diversity of tea polysaccharides.Polysaccharide was extracted from tea of 7 cultivars, and its composition and activity was analyzed. The results showed that there were obvious differences not only in extracting rate, but also in content of neutral sugar, uronic acid and protein of TPS, which led to different inhibiting effects on hydroxyl radical ( OH) and superoxide anion radical (O2-). In view of this, diversity existed in characteristics and bioactivities of TPS among tea cultivars.During the growth of tea shoot, TPS decreased gradually with maturity of fresh leaves. TPS of the second leaf from bud contained the most neutral sugar, uronic acid and protein and had the best clearing effects on OH and O2-. Compared with leaves, content of TPS in stems was lower, and the older stem got, the less TPS it contained. Although there were higher contents of neutral sugar, uronic acid and protein in TPS from stems, these TPS activity was poorer in scavenging OH and O2-. Consequently, it was revealed that bioactive polysaccharide mainly existed in leaves especially growing vigorously and varied in sugar compositions or structure between leaves and stems.Oolong tea, green tea and black tea were made respectively from same fresh leaves plucked from Fudingdabai in Hubei, Shuixian in Fujian and Dayecha in Yunnan areas. It was found that the extracting rate of GTPS was more than OTPS, and that of BTPS was the lowest in three kinds of TPS. Neutral sugar, uronic acid and protein in TPS alsoIshowed the same changes. However, there were no obvious differences in neutral sugar content between GTPS and OTPS from Fujian or Hubei. The tendency of the inhibitory rate of OH and O2- was OTPS>GTPS>BTPS, but TPS from different regions had different effects on clearing free radicals.3.The formation characteristics of Oolong tea polysaccharidesDuring the process of Oolong tea, the extraction rate of TPS and the contents of its neutral sugar and protein decreased, particularly notably after the third shaking, but the content change of uronic acid was less. The relative activity of -Glucosidase and protease increased before the third shaking , and then decreased on Zuoqing stage , which resulted in the degradation of sugar and protein in TPS . It was also indicated that there were same tendency between the inhibiting effects on radicals and activity of those enzymes. According to the changes of polyphenols content, when it was retained 85%, the content of TPS was highest and the effect on scavenging OH and O2- was best, which was regarded the technical index to end shaking during t...