Analysis of Chemical Composition Change and Coupling with Temperature and Humidity in Box Cured Tobacco Leaves
To investigate the spatiotemporal coupling relationship between tobacco quality formation and temperature-humidity fields during box-type curing,real-time sensors were employed to monitor temperature and humidity at different locations within the curing barn.Temperature and humidity field cloud maps were constructed,chemical composition changes were analyzed,and a comprehensive evaluation of post-curing tobacco quality was conducted based on the analytic hierarchy process,aiming to reveal the relationship between temperature-humidity fields during box-type curing and the formation of tobacco quality within the curing chamber.Results showed that temperature distribution at different levels within the chamber exhibited a pattern that the lower level had the highest temperature,followed by the middle level,and the upper level was the lowest.As the curing process progressed,high-temperature regions within the chamber tended to concentrate from the periphery towards the center.Moist air moved from the middle to the upper levels of the chamber,gradually creating a relatively high-humidity environment in the upper levels from the color-fixing stage to the drying stage.Within the same level of the chamber,the distribution of moist air followed a pattern of higher concentration in the center and lower concentration in the periphery.During the box-type curing process,compared to the middle and upper levels,the lower level had higher temperature and lower humidity,resulting in greater starch degradation,with starch content decreasing to 3.88%at the end of curing.Total sugar and reducing sugar were significantly lower than in other levels,protein degradation rate was fast,and total nitrogen content changed smoothly overall.Accumulation of aroma compounds was high,reaching 1 308 μg/g.Evaluation of post-curing tobacco quality at different levels within the curing chamber showed that the lower level had the highest comprehensive score of 0.817,followed by the middle level at 0.765,and the upper level at 0.721,indicating that the tobacco quality at the lower level of the chamber was optimal.These results demonstrate that tobacco leaves in the lower level of the chamber,where temperatures are high and relative humidity is low,experience greater degradation of starch resulting in higher accumulation of aroma compounds,total sugar,and reducing sugar,and superior post-curing tobacco quality.
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