Effects Of Curing Temperature, Humidity,and Time On Inclusions And Quality Of Flue-cured Tobacco Leaf

The effects of curing temperature, humidity, and time on inclusions and quality of flue-cured tobacco leaf were studied by using the electric oven with automatic temperature and humidity. The results showed that :(1) The degradation quantity of starch, degradation rate, relative residual amount decreased gradually during flue curing process. The laws were that all indexes were the biggest before 38℃, lower from 38℃to 54℃, the minimum after 54℃. Prolonging the curing time of yellowing stage could reduce the leaves starch content effectively, degradation quantity was about double of the conventional treatment, when the effect of prolonging color fixing stage was not obvious. Increasing humidity of yellowing stage was more conducive to the degradation of starch than color fixing stage.(2) With flue Curing, chlorophyll had the similar degradation laws in different teatments. The laws were that chlorophyll content decreased continuously, and the degradation quantity of yellowing stage was the largest. The degradation quantity and degradation rate of chlorophyll were the biggest before 38℃, then descended rapidly from 38℃to 42℃, at last stabilized. While the residual amount was also stable after 42℃. Chlorophyll content decreased under increasing humidity or prolonging time of yellowing stage. But the effect of treatment in color fixing stage was not obvious. T6 was the most favorable to degradation of Chlorophyll.Change of carotenoid content was unstable, the degradation quantity, degradation rate, residual amount were still the maximum before 38℃, stable after 42℃. Carotenoid content after increasing humidity or prolonging time was higher in yellowing stage than in color fixing stage. Carotenoid content of T5 was the highest. Carotenoid content of T2 was the lowest.Overall the ratio of carotenoid and chlorophyll content tended to increase, T5 had the highest ratio. Combined with the change of appearance quality of different treatments, it indicated that improvement of curing environment, increasing carotenoid content appropriatly, and promoting the degradation of chlorophyll could improve appearance quality of flue-cured tobacco leaf.(3) During curing, the variation laws of dry matter of leaves were similar, the weight of dry matter showed decreasing trend, which declined sharply before 38℃, slowed down from 38℃to 54℃, was stable after 54℃. Increasing humidity could increase respiration of tobacco leaves, and prolonging time could maintain respiration for a long time, resulting in loss of dry matter to increase 3.8~5.3 percentage. Dry matter loss of T6 was the largest, then T3.During curing, dry matter amount of tobacco veins reinforced a downward law which was different from leaves, the amount changed little before 42℃, decreased more markedly from 42℃to 54℃, and then slowed down. To effects of increasing humidity and prolonging time, prolonging time could promote dry matter loss of tobacco veins to increase 3.5~5.3 percentage. Integrated humidity and time factors in the treatments, T5 had the largest dry matter loss of tobacco veins.(4) Increasing humidity or prolonging curing time was conducive to accumulation of sugar and degradation of starch, total nitrogen, protein in cutters and uppers of flue-cured tobacco leaf. T6 was on behalf of degradation of big molecule matter and formation of chemical quality in the two parts of flue-cured tobacco leaf.(5) All treatments could increase petroleum ether extract content of the cured leaves. After increasing humidity, the content of petroleum ether extract at first increased and then decreased, which indicated that humidity should not be too high. And increasing humidity properly in yellowing stage was the most effective. while the delay effect was not obvious. Analysis of variance showed that, T6, T3 were the most favorable to accumulation of petroleum ether extract of flue-cured tobacco leaf.(6) The amino acid content of all treatments was higher than that of the control treatment at different extent. After increasing humidity, the content of free amino acids increased at first and then decreased, which indicated that humidity should not be too high. And increasing humidity properly in color fixing stage was the most effective. Prolonging curing time, particularly that of color fixing stage, the content of free amino acids was higher. The amino acid content of the leaves cured by T5 was the highest in the two parts.(7) Increasing humidity of yellowing stage which was just the reverse of color fixing stage could improve the content of neutral aroma components in cutters of flue-cured tobacco leaf effectively. When prolonging curing time of yellowing and color fixing stage, in addition to benzyl alcohol reduced 17.76%, 12.2%, the rest of ingredients increased at different extent. The effect of prolonging color fixing stage was better than that of yellowing stage.Overall increasing humidity was negative to the neutral aroma components in uppers of flue-cured tobacco leaf. Prolonging curing time of yellowing and color fixing stage could improve the content of neutral aroma components at different extent.Compared with the upper leaves, cutters was fitter for the craft of increasing humidity or prolonging curing time. The effect of increasing humidity or prolonging time on the content of neutral aroma components decreased with the rising of the part of flue-cured tobacco leaf. In different curing treatments, T6 was better than the others, then T3, T4. It showed that prolonging time on the improvement of aroma had positive significance.(8) In all treatments , the appearance quality of the cured leaves were better than that of the control treatment, although appearance quality of upper leaves after curing was significantly lower than that of cutters. The two parts showed a similar law, increasing humidity or prolonging curing time was conducive to increase orange and the classy leaves proportion, reduce lemon, cyan vein and the medium leaves proportion. But high humidity was not conducive to maximizing appearance quality. Appearance quality of the leaves cured by T6 was the best.(9) Sensory quality of the cured leaves was improved at some extent. Overall the leaves showed good aroma quality, sufficient aroma quantity, light undesirable taste, slight irritation, more comfortable aftertaste, moderate physiological strength, medium consistence. Combustibility and ash were respectively the "strong" and "white" grade. Total score of T6 was the highest (86.4 points), then T3 (86 points). The two scores were respectively higher by 2.6 points ,2.2 points than that of T1 , indicating that sensory quality of the leaves cured by T6 was the best.