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The composition and content of aroma substances in flue-cured tobacco (Nicotiana tabacum L.) will affect the quality of tobacco. To investigate the correlation between various aroma substances of K326 before and after flue-curing, and their impact on tobacco quality and diversity, this study employed the middle leaves of K326 and KRK26 as test materials. Samples were collected both before and after flue-curing for untargeted metabolomics analysis. The results of K326 showed that 584 metabolites were significantly different and there were 44 aroma-related metabolites, including alcohols, aldehydes, phenols, organic acids, etc. The analyzed aroma compounds consist of 37 known tobacco aroma substances, while 7 metabolites, previously not associated with tobacco aroma, have been identified as aroma substances in other food products. These findings suggest that these seven metabolites might may be potential tobacco aroma compounds. Further analysis showed that the content of phenols, alcohols, and aldehydes increased significantly after flue-curing, but the content of organic acids decreased. Furthermore, the analysis of KRK26 revealed a correlation between the quantity of aroma substances and the type of tobacco. These findings serve as a reference for enhancing the flue-curing process of K326 and optimizing the industrial production of cigarettes that use cured K326 tobacco leaves.

Nitrogen fertilizer is essential for the yield and quality of flue-cured tobacco. Honghuadajinyuan (i.e. Hongda) is a special flue-cured tobacco variety in Yunnan, which differs in nitrogen application rates from other varieties. In 2016 and 2017, different nitrogen application rates were established in Yunnan to compare, with other varieties, Hongda's agronomic, economic, chemical indicators and soil residual nitrogen. As nitrogen fertilizer rate increased, the ratio of fresh weight to dry weight (RFD) and the proportions of inferior tobacco (PIT) initially decreased and then increased in contrast to the proportions of superior tobacco (PST) and average price. Total sugar and reducing sugar contents in flue-cured tobacco leaves decreased as nitrogen fertilizer rate increased, while total nitrogen, nicotine, and protein contents increased. The highest sensory evaluation scores were obtained with 45 and 60 kg N ha−1. Soil nitrate contents increased with increasing nitrogen fertilizer rate and significantly increased when nitrogen application rate exceeded 60 kg N ha−1. A quadratic model was suitable for Hongda's response to nitrogen fertilizer rate and 60 kg N ha−1 can meet the needs of the growth of this flue-cured tobacco variety. Abbreviations: Hongda: Honghuadajinyuan; RFD: ratio of fresh to dry weight; PIT: proportion of inferior tobacco; PMT: proportion of medium tobacco; PST: proportion of superior tobacco; SPAD: soil and plant analyzer development. [ABSTRACT FROM AUTHOR]