| High-quality tobacco-leaf raw-materials is the foundation to support the development of Chinese tobacco industry, especially in the basis and key for the development of Chinese-style cigarettes. But comparing Chinese tobacco raw-materials quality with foreign high-quality tobacco leaf, our country's tobacco leaf is with lower quality, which mainly manifested in the characteristics of aroma and smoke. As the ecological factors restrict the formation of high-quality flue-cured tobacco aroma style, flue-curing determines the style characteristics formed and accumulated in the course of agronomic that if it could demonstrate. Therefore, in order to study the factors affecting the flavor quality of flue-cured tobacco, it is important to find out the relationship between flue-cured tobacco aroma style and the related factors and transformation rule that will help to improve the level of modern tobacco production, the overall efficiency and international competitiveness of tobacco products. Additionally, it might accelerate the promotion of the domestic tobacco leaf quality generally, to improve the industrial utilization efficiency of tobacco, and to reduce gradually the reliance on importing. Thereby, this paper study the impacts on some factors as light, water, nutrient to aroma content of flue-cured tobacco and the transformation discipline of aroma precursors to volatile aroma substances in different maturity of tobacco during flue-curing process. The main results are as follows:1. The relationship between light intensity and aroma metabolism in the flue-cured tobacco was studied by decreasing the light intensity. The results showed that low-light intensity did not only increase leaf length, leaf width, plant height and thin stems, but also affected the aroma of the tobacco and chemical composition. Light intensity and quality of flue-cured tobacco plastid pigment (chlorophyll,β-carotene, lutein), and polyphenols (chlorogenic acid and rutin) content was positively related to reduced light intensity. The aroma precursor content decreased when reduced light intensity. The total nitrogen, potassium content and leaf PPO and POD activity increased while nicotine, total sugar, reducing sugar content decreased when decreasing light intensity. The main aroma precursor content and chemical content in different parts was influenced differently by the light intensity.2. UV-B intensity is closely related to plastid pigments and polyphenols of flue-cured tobacco, enhanced UV-B in a certain range could increase the plastid pigments and polyphenols content of flue-cured tobacco. Enhanced UV-B intensity below 0.55W/m~2 on the upper leaves would increase carotenoid content. Carotenoid in the upper leaf showed a gradual downward trend with the increased UV-B intensity. Enhanced UV-B intensity at the range of 0.55W/m~2～3.25W/m~2, carotenoid content in tobacco leaves increased due to UV-B intensity. Enhanced UV-B intensity would lead to polyphenols content of the upper leaves of tobacco at a mature stage increasing and the amplitude with UV-B intensity was proportional. Increase UV-B irradiation to the middle leaves could inhibit chlorogenic acid and rutin of tobacco synthesis, the reduction with UV-B intensity was proportional. Centered in strong UV-B radiation longer, when after the cessation chlorophyll and carotenoid content of tobacco decreased gradually. Strong UV-B irradiation on tobacco in a relative short period that the cells of tobacco leaves had a gradual recovery trend of chlorophyll and carotenoid and metabolic balance. Furthermore, the recovery speed of lutein was faster thanβ-carotene. Enhanced UV-B would lead to total sugar, reducing sugar, total nitrogen, protein, nicotine content decreased while potassium content increased in flue-cured tobacco.3. Different water stress from vigorous growth stage to maturity stage of flue-cured tobacco was studied. The results indicated that water had an important effect on aroma content and chemical composition of flue-cured tobacco. In vigorous growth stage, drought and flooding inhibited extremely on the leaves growth and development of flue-cured tobacco. Inundation stress in both periods were extremely unfavorable to form the anabolic of aroma precursors of flue-cured tobacco in different periods. Generally speaking, continuous drought in vigorous growth stage was harmful to metabolic formation of aroma precursors in tobacco leaf while it in maturity stage was beneficial to aroma precursors accumulating.4. Main nutrient elements to the development of tobacco growth, glandular hairs and aroma precursors content of tobacco were critical. The main nutrients deficiency had a negative impact on growth of tobacco and had a significant impact of growth and development on glandular trichome. As the significant leaf area reduction and a stimulating effect of growth on glandular trichome, various types of glandular trichome density increased corresponding in N deficiency treatment, and P, K, Mg deficiency would result in the various types of trichome density greatly reduced to effect in tobacco leaves. Major nutrient elements deficiency would impact seriously on the main aroma precursors of flue-cured tobacco. N, K, P, Mg deficiency would extremely inhibit plastid pigments and polyphenols anabolic formation, N deficiency affected on carotenoid the most, P, Mg deficiency was followed, K deficiency affected the least while P deficiency affected on polyphenols the most. Mg, K deficiency was followed, N deficiency affected the least. Therefore, to maintain N, P, K, Mg adequate reasonably supply in the pre-mature period of flue-cured tobacco production and to study balance fertilization further were very important to improve the aroma style and quality of Chinese flue-cured tobacco.5. It was the first time to study systematically on transformation of aroma precursors the changes discipline of the formation of aroma substances in the process of flue-curing. In the process of unripe leaves, mature leaves and over-ripe leaf material of cv.K326, Yunyan 85 and HD, the changes in physical characteristics and aroma precursors were quite different in different maturity leaves, breeds and aroma transformation. Results indicated as following: 1) Evaporation and the amount of dry matter with different flue-curing temperature of different varieties tobacco were from 40°C to 50°C which was a critical stage to control the rate of water loss. Especially to HD, the loss of water was less speedy than K326 and Yunyan85, at this crucial stage should control water loss speed and heating slowly. Water loss rate and loss of dry matter volume did not change greatly in baking process. As a result, harvesting unripe lower leaves of tobacco would not affect the quality.2) The chlorogenic acid and rutin in cv.K326 and Yunyan 85 leaves showed a downward trend after the first rising, chlorogenic acid and rutin content increased of post-curing tobacco ultimately. The chlorogenic acid and rutin content in HD leaves showed a down-up-down trend. The temperature between 40-55°C was a crucial period to polyphenols transformation in flue-cured, the decline speed of temperature in curing barn was the key to polyphenols and transform.3) The lutein andβ-carotene in leaves of K326, Yunyan85 and HD changed greatly in the curing process. The lutein andβ-carotene in leaves of K326 and Yunyan85 degraded completely in the yellowing stage. When the curing barn temperature was over 40°C, the carotenoid content remained generally stable. The degradation temperature range of carotenoid in HD leaves was much larger than the other two species, which had twice degradation stage during the process. The lutein andβ-carotene degradation rate of unripe leaves was the largest, over-ripe leaves was the second, the mature leaves was the least. The lutein andβ-carotene content of unripe leaves was the highest in the three mature leaves, and from this point of view, harvesting unripe leaves would be better.4) The main ingredients in pre-curing leaves were Neophytadiene, 4,8,13-Cyclotetradecatriene-1,3-diol, 1,5,9-trimethyl-12-( 1 -methylethyl)-, Thunbergol. The plastid pigment an-d Siebel alkane compounded and their degradation products were the main ingredient. Yellowing period and the color-fixing period were major periods of aroma materials formation into the most degradation of the plastid pigments and of Siebel alkane compounds were degrading in this time, particularly the color-fixing period.5) As the maturity of flue-cured tobacco increasing, the aroma components were gradually increasing. Mature leaves always had the highest total amount of aroma substances in the curing process, over-ripe leaves. Secondly, unripe leaves were the lowest. Considering of aroma quality and aroma volume, it is better to harvest the mature tobacco leaves.
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