| In this paper, two kinds of Virginia tobacco, K326 and Yunyan85, were studied for the mechanism of Browning of tobaccos. The result as the following:1. An scientific method was set up for measuring the value of tobacco leaves during aging time.Wsl-2 timiter is used to measure the value of liquid, solid and colloid, especially in oil paint. The color value of the liquid extracted from tobacco leaves by water can be measured to indicate the Browning of them. Alcohol and light petroleum also can be tested to distill the material of color, The result indicated water is batter than the others2. The system condition of measuring chlorogenic acid by HPLC. Chromatographic column is ODS-C18(5μm, 250 mm×4.6 mm; waters),the flowliquid is acetonitrile : water: methanol: phosphoric acid equal to 12: 85.5: 3: 0.5. The velocity of flow is one milliliter per minute. The temperature of chromatographic column is thirty degree Centigrade and the wavelength of detection is 326 nanometer. The apex comes out at the fourteenth minute, and end up at sixteenth minute. The performance of this system is good enough to measure the content of chlorogenic acid.3. The relation between the content of chlorogenic acid and Browning.The content of the chlorogenic acid fade away during aging time. The longer its aging, the less its lefting. But the color of tobacco leaves becomes deeper while the chlorogenic acid is reducing. The result indicated that the Browning of tobacco leaves during the first year is decided by oxidation reaction of chlorogenic acid, the R2 of K326 is 0.931 and the R2 of Yunyan85 is 0.9806. It means that the oxidation play an important role in the Browning of tobacco leaves. After that, the relationship between the oxidation of chlorogenic acid and the Browning become lower than before. The R2 of K326 is 0.1169 the R2 of Yunyan85 is 0.0009.It indicated that the Browning did not decided by the oxidation of chlorogenic acid.4. The influence of environment factor on the Browning The Browning during aging time mainly infected by oxygen, temperature and humidity. The result indicated that the Browning mainly effected by oxygen that because the color of tobacco leaves has changed very little without oxygen, However, when tobacco leaves contacted with atmosphere, they change a lot, For example, the color value of K326 added by 9.5 and the color value of Yunyan85 added by 11.9, It is nearly as half and one times as of that without atmosphere.Humidity is another factor that effected the Browning, from 30% to 70%, after six months, the color value of K326 added by 6.8 and the color value of Yunyan85 added by 8.5. The temperature, if the water content of tobacco leaves between 11%-12.5%, did not effect the Browning a lot. The color value of K326 added by 3.8 from 20℃to 40℃,and Yunyan85 added by 5.4 in the same situation .5. The influence of microbe live on the tobacco leafSix different kinds of microbe which have polyphenol oxidase were separated and purified from the leaf of K326 and Yunyan85, and were marked as A,B,C,D,E and F. The polyphenol oxidase of B,D,E is more active than the others. The number of microbes and the kinds of them are most in the sixth month of aging. The result indicated that the microbes live on the tobacco leaves who may play an important role in the first six months , but it infected by the water content of the leaves.6. A method of controlling BrowningA method, according to the result of the experiment, could be used to control the Browning of tobaccos. First, dry the tobacco leaves until the water content is between 11%-12.5%, And then, put them in bags and seal up the bag so that keep off oxygen, At last, keep them in the room under 20℃.The result indicate the color value of K326 isl6.3and Yunyan85 is 17.8 in experiment group, and the color value of K326 is 23.4 and Yunyan85 is 25.8 in the control group. The color value of the control group is as a half and one as times of experimental group, so this method is useful.
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