| The maturity degree is core factor affecting the quality and the classification of tobacco leaf, therefore, the determination of harvest time is a key step for getting the high quality tobacco in the production.. At present, it can only rely on human experience to divide the maturity of tobacco leaf; however, there are lots of tobacco varieties in China, the culture environmental conditions in many areas are different, and their cultural measures are also various. So the picked-leaf maturity of tobacco in the field is difficult to master. In this experiment, the effect of M1 to M5 five different picked-leaf maturity degrees on the tissue structure and the physiological and biochemical characteristics of the fresh leaf were studied, with tobacco leaves from upper, middle and lower part of "Honghuadajinyuan" and K326 flue-cured tobacco as materials, planted in Kunming Xundian and Shilin. And analysis of the relationship between maturity and tissue structure and chemical components and the sensory quality of tobacco leaves. The aim is to reveal the change of the quality during the ripening of tobacco leaf, to explore whether it is possible to quantify some indicators, in order to guide the timely harvest of tobacco leaf in the actual production process in the future. The main results show that:1. With the maturity of M1 increase to M5, the structure of tobacco leaves changes from tight to loose. The leaf thickness, the palisade and spongy tissue thickness of the tobacco leaves increased firstly and then decreased, and M2 to M4 maturity was the obvious turning point. The tissue ratio, ratio of the gate leaf and epidermal thickness of tobacco leaves affected by harvesting position and planting regions. There was no significant correlation between the change of epidermal thickness and maturity. Tobacco sensory quality and structure in M3 maturity is best, showed that the leaf structure was loose, the leaf thickness and the palisade and spongy tissue thickness were thicker, tissue ratio was relatively large in the range of 0.9 to 1, which all conducive to harvesting the high quality tobacco, which can help to determine the appropriate maturity.2. With the increase of maturity from M1 to M5, the amylase activity increased firstly and then decreased, the total nitrogen content and nitrate reeducates activity gradually reduced. The content of soluble protein was affected by variety and planting regions, and did not show a better regularity in this study. The role of amylase is to produce sugar, has a greater contribution to aroma quality. Our study found that M3 maturity had higher amylase activity, which is consistent with the sensory quality results, showed that higher amylase activity, basic value standard of amylase activity around 2 was closely related to sensory Quality, which can be used as a standard for judging the maturity. Although, nitrate reductase and total nitrogen and protein content are closely related to leaf quality, but the large difference between the varieties and regions, may not be suitable as a unified standard for judging the maturity of tobacco leaf..3. As the important materialand and aroma precursors of tobacco leaf, the content and composition of the pigment can affect the final leaf quality. Research results show that, with the increase of maturity, the chlorophyll a and b, carotenoid pigment and the total pigment content decreased gradually, but the percentage of carotenoid in total pigment content increased gradually. During the maturation of tobacco leaves, chlorophyll content degraded fastrer than the carotenoid content. Although the change of pigment content and percentage of the regularity is significant, but them had great differences in different varieties and different years. Among them, content of pigment of Hongda was higher than K326, the percentage of carotenoid was lower, the pigment content and the percentage in 2015 were higher than 2014. Results showed that pigment content and percentage was affected by various factors such as variety, climate and so on, which may not be suitable for use pigment content as quantitative criterion for maturity.4. With the increase of maturity from M2 to M4, the content of total sugar, reducing sugar, starch, chlorideion, and petroleum ether extracts increased, but the content of total nitrogen, nicotine and potassium decreased; Sugar-alkali ratio, sugar-nitrogen ratio and chloride-potassium ratio rose, but nitrogen-alkali ratio declined, content of carbohydrate in M3 maturity was higher, the content of nitrogen compound was middle, the Sugar-alkali ratio was in 8-13 rang, the nitrogen-alkali ratio was between 0.7 to l,the content of alcohols, ketones, and N-heterocyclic compounds and esters and lactones were higher, content of phenol and aldehyde compounds were middle, neophytadiene was lower. In this study, the best sensory quality of the tobacco leaves is the M3 maturity, the general trend is M3> M2> M4. It could be concluded that indicators mentionded above are closely related to the high leaf quality. Some indicators changes regularly and can provide a more reliable standard of maturity, such as Sugar-alkali ratio nitrogen-alkali ratio, content of ketone compounds and so on. |
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