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Article

The Effects of Increasing the Dry-Bulb Temperature during the Stem-Drying Stage on the Quality of Upper Leaves of Flue-Cured Tobacco

by
Jingxiao Jia
1,
Mingjin Zhang
2,
Jinchao Zhao
2,
Jian’an Wang
1,
Fan He
1,* and
Lifang Wang
2,*
1
College of Tobacco Science, Henan Agricultural University, Zhengzhou 450002, China
2
Luzhou Branch Company of Sichuan Provincial Tobacco Company, Luzhou 646000, China
*
Authors to whom correspondence should be addressed.
Processes 2023, 11(3), 726; https://doi.org/10.3390/pr11030726
Submission received: 11 January 2023 / Revised: 21 February 2023 / Accepted: 25 February 2023 / Published: 28 February 2023
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Versions Notes

Abstract

:
The control of the curing temperature during the stem-drying stage is important for the quality of upper leaves of flue-cured tobacco. Based on the conventional curing process during the yellowing stage and the leaf0drying stage in the tobacco curing process, in this study, the dry-bulb temperature was increased to 72 and 75 °C in the bulk curing barn during the stem-drying stage to compare with the highest temperature of 68 °C commonly adopted in the bulk curing barn. The result showed that, compared with the conventional temperature setting, the energy consumption cost was reduced by 0.10 or 0.08 USD/kg when the curing temperature was increased to 72 or 75 °C, respectively. Statistical analysis showed that increasing DBT was beneficial to the improvement in the internal quality of flue-cured tobacco leaves. The adjustment of curing temperature also improved the aromatic quality and volume of singe-material tobacco leaves. However, as the temperature continued to increase, the quality improvement in cured upper tobacco leaves showed a decreasing trend. According to the quality of fresh tobacco leaves, an appropriate increase in the dry-bulb temperature based on the conventional temperature setting of 68 °C during the stem-drying stage can improve the usability and economic benefit. The degree of increase in the DBT should depend on the quality of local fresh tobacco growth in the field.

1. Introduction

The treatment of upper leaves (ULs) of flue-cured tobacco stalks is of great importance for the formulation of thin cigarettes and the reduction in tobacco tar and harm to human body. However, the current production of upper tobacco leaves still faces numerous problems, including residual ash on leaves, offensive odor, and insufficient aroma, which seriously restrict the usability of cigarette formulation using ULs [1,2]. Many scholars have tried to improve the quality of the upper tobacco leaves from different perspectives, including cultivation, tobacco leaf maturity, and curing [3,4,5]. Among these, the curing of tobacco leaves is considered to be an essential factor to ensure the quality of ULs of flue-cured tobacco. The curing process comprises the yellowing stage, leaf-drying stage, and stem-drying stage (SDS) [6]. The SDS represents the key stage as it can promote the degradation of the yellowing stage [7], maintain the compounds [8] in the leaf-drying stage, completely dry the tobacco leaves, and produce a unique aroma of flue-cured tobacco [9]. To improve the curing quality of ULs, Xu et al. [10] set a temperature of 60 to 68 °C for the SDS and found that keeping the highest temperature within a reasonable range is conducive to the accumulation and transformation of aroma substances of flue-cured tobacco. Bortolini et al. [11] indicated that a higher maximum dry-bulb temperature (DBT) can save energy and reduce costs, and the sensory quality of the flue-cured tobacco leaves can also be improved. However, few papers can be referenced regarding the control of the DBT during the SDS. Based on this, this paper studied the effect of increasing the DBT from 68 °C at present [12,13] to 75 °C during the SDS on the quality of the upper leaf of flue-cured tobacco, in order to provide guidance for the bulk curing barn (BCB) curing process for UL.

2. Materials and Methods

2.1. Experimental Materials

The experiments were carried out in Liangjiazhuang, Zhuyang Town, Lingbao City, Sanmenxia, Henan Province, and Jianzhu Tobacco Station, Gulin County, Luzhou City, Sichuan Province from 2019 to 2021. The local popular flue-cured tobacco, Yunyan 87 (Nicotiana tabacum L., Yunnan Tobacco Research Institute, Yuxi, China), was selected for this experiment, which is planted over more than 13.33 million hectares every year in China [14]. The cultivation management of the tobacco field was in compliance with the local production practice for high-quality tobacco leaves. From the tobacco plant, the top 4 to 6 leaves were taken as experimental materials. The experimental materials were evenly grown with similar appearance and size. The local production practice comprises harvesting, braiding, and loading. The tobacco leaves having similar sizes were harvested from the upper tobacco leaves and braided into 10 sticks as the marked tobacco leaves. The marked tobacco leaves were hung in the middle of the middle beam of the BCB for curing. The tobacco leaves were cured in the BCB, which was built in 2009, with descending air flow in the loading chamber according to the No.418 document of the Chinese State Tobacco Monopoly Administration.

2.2. Experimental Design

The yellowing stage and the leaf-drying stage were carried out according to the local BCB curing process, and three experiments were set up in the loading chamber of the BCB during the SDS process. The experimental design is shown in Table 1. The three treatments were started at the same time, and each treatment was set as 3 repetitions in each location.

2.3. Testing Items and Methods

2.3.1. Energy Consumption Cost

The experimental data were recorded and calculated, including loading fresh tobacco leaf volume, total volume of cured tobacco leaves, coal consumption, electricity consumption, coal consumption per kilogram of cured tobacco leaves, electricity consumption per kilogram of cured tobacco leaves, coal consumption cost per kilogram of cured tobacco leaves, electricity consumption cost per kilogram of cured tobacco leaves, and the total energy consumption per kilogram of cured tobacco leaves.

2.3.2. Indoor Testing

After the UL curing processes were finished in the BCB, the tobacco grade characteristics of 8 sticks of tobacco leaves among the 10 sticks were classified by a professional according to the Chinese national standard GB2635-1992. Statistics of economic benefits were contrasted according to the market purchase price of the tobacco grade. In addition, the marked tobacco leaves of the other 2 sticks used for the three treatments were separately packed, and 2 kg was randomly taken from each package and returned to the laboratory in sealed bags. The cured tobacco leaf samples were removed from the main stem, placed in an oven (VO-6020, Shanghai ruyi company, Shanghai, China) at 40 °C, dried for 12~16 h until they could be crushed by fingers, cooled at indoor temperature, crushed by a grinder (Bilon-DFT-100A, Shanghai Bilong, Shanghai, China), passed by a 40-mesh sieve, and placed into a vacuum bag for storage.
The items used to test the inherent quality of the cured leaves included conventional chemical compositions, petroleum ether extract content, and the composition and contents of neutral aroma substances. The conventional chemical compositions of tobacco leaf samples were analyzed using near-infrared spectroscopy (TD-NIRS, Aunion Tenh Co., Ltd. Shanghai, China) and quantitative analysis technology, using an integrating sphere diffuse reflectance detector and a gold-plated diffuse reflector as the background [15]. The determination of petroleum ether extraction content referred to the Chinese standard YC/T 176-2003 “Determination of petroleum ether extract from tobacco and tobacco products” [16].
The conventional chemical compositions of neutral aroma substances used dichloromethane as the extractant to extract the aroma of the crushed tobacco leaf samples, and then concentrated the result into 1.0 mL of a concentration solution using a rotary evaporator (Are-2000A, Shanghai Jinlan, Shanghai, China) with pressure of 560 MPa and rotating speed of 65 r/min [17]. The concentration solution was analyzed using a gas chromatograph (GC6890N/MS5975 I, Agilent, CA, USA) with naphthalene as the internal standard substance. The obtained chromatogram was retrieved by NIST05, Wiley 275 computer library, and the phase-pair content of each component was calculated according to the internal standard calibration normalization method.

2.3.3. Sensory Quality Evaluation on Flue-Cured Tobacco Leaves

The single-material tobacco removed from the stem was formulated with reference to the literature [18]. After moisture regained in a constant temperature and humidity box (BINDER KBF240, Tuttlinger, Germany) with the temperature set at 25 ± 0.5 °C and humidity set at 80 ± 1.5% for 24 h, the tobacco leaf samples were cut into widths of 0.8 mm with a special tobacco cutter, and the cut tobacco was gently filled using a single-material maker (GIZEH Raucherbedarf, Cologne, Germany) into an empty cigarette with a filter tip to make a cigarette with a weight of 900 ± 15 mg and a length of 85 mm. The sensory quality evaluation of cured tobacco leaves was evaluated by 5 experts from Chinese State Tobacco (Henan) Industry Co., Ltd. in accordance with the industry standard YC/T 530-2015 tobacco and tobacco products. Seven indicators were scored, including aromatic quality, aromatic volume, offensive odor, gaseous concentration, strength, irritation, and aftertaste.

2.3.4. Statistical Method of Data

SPSS 26.0 statistical software was used to analyze the variance in the data and to carry out a stepwise regression analysis of the DBT of the SDS of each treatment and the inherent quality indexes of the cured tobacco leaves, with the total sugar (Y1), reducing sugar (Y2), nicotine (Y3), K+ (Y4), Cl− (Y5), total nitrogen (Y6), and petroleum ether extract (Y7) as the dependent variables, and the DBT of the SDS of each treatment as the independent variable (x), According to the curve estimation results, the regression equations Y1–Y7 between the DBT of the SDS and the quality index of cured tobacco leaves under different treatments was established.
Excel 2017 was used for data processing. Duncan’s test was used for multiple comparisons to detect significant differences. Origin 2021 analysis software was used for drawing.

3. Results and Analysis

3.1. Effect on the Energy Consumption Cost

It can be seen from Figure 1 and Table 2 that the two treatments effectively shortened the stem drying curing time after the DBT increased during the SDS. In particular, the time for the SDS was obviously reduced as the DBT increased. At present, the curing of tobacco leaves is undertaken manually. Shortening the curing time in the SDS is beneficial to saving labor costs. The two treatments reduced the energy consumption due to rapid dehumidification under high temperature. In the treatments, the total energy consumption per kilogram of cured tobacco leaves in the T1 treatment was the lowest (0.60 USD/kg). The time for the SDS in T2 was the shortest. However, because the heat loss was accelerated by the furnace structure of the BCB, the total energy consumption cost per kilogram of cured tobacco leaves was slightly higher than that of T1, but still lower than that of CKs.

3.2. Effects on Economic Characters of ULs of Flue-Cured Tobacco

The top-class ratio, middle-class ratio, and average price of selling are important characteristic parameters of cured tobacco leaves [19]. The increase in the temperature during the SDS significantly affected the economic characteristics of the upper tobacco leaves. It can be seen from Figure 2 that the proportion of top-class tobacco in T1 and T2 treatments was significantly higher than that in CK treatment, and the proportion of middle-class tobacco was lower than that in CK treatment. The ratio of top-class to middle-class tobacco with different treatments was ranked T1 > T2 > CK. Regarding the average price, T1 had the highest average price. The average price of cured tobacco leaves with different treatments was ranked T1 > T2 > CK.

3.3. Effects on Conventional Chemical Compositions of UL of Flue-Cured Tobacco

It can be seen from Table 3 that with the increase in the maximum DBT in the SDS, the total sugar and reducing sugar of ULs first increased and then decreased. The contents of total sugar and reducing sugar were significantly varied in different treatments and reached the maximum in the T1 treatment. The total nitrogen and nicotine decreased and reached the minimum in the T2 treatment. The total nitrogen content varied significantly among the three treatments, and the content difference of nicotine was significant between CK and the others, and insignificant between T1 and T2. K+ and Cl− increased first and then decreased and reached the minimum in the T1 treatment. The content difference of K+ was significant between T1 and the others, but insignificant between CK and T2. The content difference of Cl− was significant between CK and T1, but insignificant between T2 and the others.

3.4. Effects on the Content of Petroleum Ether Extract in UL of Flue-Cured Tobacco

The petroleum ether extract of flue-cured tobacco is a mixture of organic substances obtained through distillation and extraction with petroleum ether as a solvent [20]. The petroleum ether extract of flue-cured tobacco is an important component in tobacco leaves that affects the quality and aroma of tobacco leaves [21]. It can be seen from Figure 3 that the appropriate increase in DBT during the SDS can increase the content of petroleum ether extract. The ratio of petroleum ether extract content in different treatments was ranked T1 > T2 > CK. The content difference was significant among the treatments.

3.5. Effects on Sensory Quality of UL of Flue-Cured Tobacco

It can be seen from Table 4 that with the increase in the maximum DBT during the SDS, the aromatic quality, aromatic volume, offensive odor, irritation, and aftertaste of the cured tobacco leaves of each treatment first increased and then decreased. The strength and concentration of the flue-cured tobacco leaves of each treatment first decreased and then increased. In terms of performance indicators, T1 can improve the aroma quality, aroma volume, and aftertaste score compared with CK, while T2 can improve the gaseous concentration score of single-material tobacco. The total score ranking of different treatments was T1 > T2 > CK.

3.6. Effects of Temperature Increase during the SDS on the Appearance of the Upper Leaves of Flue-Cured Tobacco

It can be seen from Table 5 that with the increase in the maximum DBT in the SDS, the appearance of the upper leaves of flue-cured tobacco was significantly improved, including the increase in tobacco tar, thinner tobacco leaves, loose structure, less surface dusting, and green content. The ranking of appearance quality of tobacco leaves after different treatments was T1 > T2 > CK. Additionally, in Appendix A are shown effects of temperature increase during the dry gluten stage on the physical characteristics of the upper leaves of flue-cured tobacco.

3.7. Effects of Temperature Increase during SDS on the Composition and Contents of Neutral Aroma Substances in the Upper Leaves of Flue-Cured Tobacco

The 31 kinds of neutral aroma substances detected by GC/MS qualitative and quantitative analysis were classified according to the aroma precursors of tobacco leaves, including 5 Maillard reaction products, 4 aromatic amino acid cleavage substances, 1 cembratriendid alkyl degrading product, 17 carotenoid degradation products, 3 other aroma constitutes, and 1 neophytadiene. Studies showed that neophytadiene is a degradation product of chlorophyll with a clear aroma. Cembratriendid alkyl is a glandular hair secretion of tobacco leaves which degrades with aroma during tobacco curing and fermentation. Phenethyl alcohol, benzylalcohol, phenylacetaldehyde, and benzaldehyde are produced with a rich aroma during the degradation of aromatic amino acid cleavage substances. It can be seen from Table 6 that an appropriate increase in the temperature during the SDS is beneficial to the metabolism and transformation of various aroma precursors in tobacco leaves, and can promote the formation of neutral aroma substances in cured tobacco leaves. Compared with CK and T2, the neutral aromatic substance of flue-cured tobacco in T1 was obviously improved. The neutral aromatic substance ranking in different treatments was T1 > T2 > CK.

3.8. Statistical Analysis between DBT and Internal Quality of Cured Tobacco Leaves during SDS

The regression equation is shown in Table 7. The equation between the DBT and the total sugar content, reducing sugar content, nicotine content, K+ content, Cl− content, and petroleum ether extract content of flue-cured tobacco leaves during the SDS had a high degree of fit, and the results of variance analysis reached a significant level on the DBT variable on the internal quality of cured tobacco leaves. However, the regression equation of DBT and total nitrogen content of cured tobacco leaves during the SDS was not well fitted, and the result of variance analysis did not reach a significant level. Therefore, more repeated tests should be undertaken to increase the sample size to continue the analysis.

4. Discussion

4.1. Analysis of the Effect of Increasing DBT during the SDS on the Energy-Saving Efficiency of BCB

The flue curing of tobacco leaves is an energy-intensive process, for which coal has conventionally been used as the primary fuel in China [22]. About 1 kg of cured tobacco leaves requires the consumption of 1.5 kg of coal, and China annually utilizes 3–4 million tons of coal for tobacco curing [23]. In this study, T1 saved 14.07% of coal consumption and 12.50% of electricity consumption under the condition of the old BCB built around 2010–2012. This new tobacco curing scheme, in which the DBT is increased, is very significant for energy conservation and emission reduction for flue-cured tobacco production. At present, China’s old BCBs are undergoing the process of transformation into green buildings, which is addressing poor sealing and insulation of roofs, walls, doors, and windows [24]. Increasing the DBT in the SDS process of flue-cured tobacco curing further reduces energy consumption.

4.2. Moderate Analysis of Temperature Increase during SDS

The growth of tobacco is closely related to the ecological environment [25,26], and the DNA methylation pattern decides the quality and styles of the fresh tobacco leaves and affects the curing characters of flue-cured tobacco [27]. In the experiment in Luzhou City of Sichuan Province from 2020 to 2021, the results demonstrated that the comprehensive performance of ULs of flue-cured tobacco was the best in the T2 treatment compared with the others (temperature during the SDS was 75 °C). However, in the experiment in Sanmenxia City of Henan Province, the results showed that the comprehensive performance of ULs of flue-cured tobacco in the T1 treatment was the best compared with the other treatments (temperature during the SDS was 72 °C). The distribution of tobacco-planting fields spans nearly 5000 km from Mudanjiang in the northeast to Lincang in southwest China [28]. The different curing characteristics of fresh flue-cured tobacco in production have also led to various control curves, which include the DBT, wet-bulb temperature, and curing keeping time [29]. Therefore, the difference in ecological environments caused by space–time conditions results in different qualities of tobacco leaves and the suitable curing temperatures during the SDS are different for different tobacco leaves. Further in-depth studies on the growth and metabolism of tobacco leaves in different areas should be carried out.

4.3. Analysis on the Effect of Increasing DBT during SDS on the Chemical Composition of Tobacco Leaves

Sensory quality evaluation is the final evaluation standard for the quality and usability of tobacco leaves, while the harmonization of chemical compositions in tobacco leaves represents an important element for the sensory quality evaluation [30,31,32]. For instance, the sugar content in cured tobacco leaves mainly comes from the degradation of starch, which requires water as a solvent to boost metabolism [33,34]. The SDS is the main stage when the water dries from the main vein of tobacco leaves. In this stage, part of the water in the main vein of tobacco leaves evaporates under high temperature, and some of the water content in the main vein transfers from the inside to the surface of the leaves due to the difference in water potential [35]. Increasing the temperature in the SDS is beneficial to the evaporation and transfer of water in the main vein of tobacco leaves, thus increasing the concentration of enzymes and the amylase activity, and promoting the starch-to-sugar conversion. The content of total sugar and reducing sugar in tobacco leaves after curing is increased. Nicotine in tobacco leaves contains free nicotine and bound nicotine, and free nicotine is easily volatilized due to the high temperature and water evaporation [36]. Increasing the temperature in the SDS can increase the volatilization of free nicotine in the tobacco leaves, so the contents of nicotine and total nitrogen in the cured tobacco leaves decrease.

4.4. Analysis on the Effect of Increasing DBT during SDS on the Petroleum Ether Extract of Tobacco Leaves

The process used to cure tobacco leaves is different from the preservation drying process used for general agricultural products. The substances synthesized in the leaf-drying stage and the SDS, such as petroleum ether extract, can better reflect the self-aroma of tobacco leaves [37]. The content of petroleum ether extract is positively correlated with the quality and aroma content of tobacco leaves [38]. Normally, flue-cured tobacco leaves with a high content of petroleum ether extract have high quality and a strong aroma [39,40]. The results of this experiment showed that the content of petroleum ether extract in flue-cured tobacco leaves increased significantly after the DBT was increased during the SDS. This may be because the shorter curing time reduces the degradation and total volatilization of petroleum ether extracts under high temperatures.

5. Conclusions

Increasing the curing DBT temperature during the SDS from 68 °C, which is currently used, to 75 °C can reduce the energy consumption cost of curing and improve the sensory quality of the tobacco leaves. Statistical analysis showed that increasing DBT was beneficial to the improvement in the internal quality of flue-cured tobacco leaves. To summarize, appropriately increasing the DTB in the SDS can significantly optimize the overall quality of the upper tobacco leaves, and increase the economic benefits of tobacco plants and the industrial usability of the upper tobacco leaves. The degree of DBT increase is dependent on the nutritional status of local fresh tobacco growth in the field.

Author Contributions

Conceptualization, M.Z. and L.W.; methodology, J.J.; software, J.Z.; validation, J.W., F.H. and L.W.; formal analysis, F.H.; investigation, L.W.; resources, L.W.; data curation, J.J.; writing—original draft preparation, J.J.; writing—review and editing, F.H.; visualization, J.W.; supervision, F.H.; project administration, L.W.; funding acquisition, J.W. All authors have read and agreed to the published version of the manuscript.

Funding

This study was funded by Sichuan Provincial Tobacco Company Luzhou City Company on research on the key technology of upper tobacco leaf curing with top-short stalk segments in Luzhou (Grant no. 2023-16).

Data Availability Statement

The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Conflicts of Interest

The authors declare no conflict of interest.

Abbreviations

Upper leaves (ULs), stem-drying stage (SDS), dry-bulb temperature (DBT), bulk curing barn (BCB).

Appendix A. Effects of Temperature Increase during the Dry Gluten Stage on the Physical Characteristics of the Upper Leaves of Flue-Cured Tobacco

It can be seen from Table A1 that appropriately increasing the temperature in the SDS affects the physical properties of the upper leaves of flue-cured tobacco. With the increase in the maximum DBT in the SDS, the thickness of the cured tobacco leaves was significantly less, the tensile strength and stretching distance were significantly increased, and the stem content and average moisture content of the tobacco leaves decreased. Among the treatments, the comprehensive performance of the T1 treatment was the best, and the ranking of the physical characteristics of the flue-cured tobacco leaves in different treatments was T1 > T2 > CK.
Table
Table A1. Comparison of physical properties of cured tobacco leaves with different treatments.
Table A1. Comparison of physical properties of cured tobacco leaves with different treatments.
TreatmentThickness (mm)Tension Resistance (N)Stem Rate (%)Average Moisture Content (%)Stretch Distance (mm)
CK0.0911.5126.7227.4110.68
T10.0661.6625.4125.7812.77
T20.0781.5726.0426.3411.59

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Processes 11 00726 g001 550
Figure 1. Comparison of time of the stem-drying stages under different treatments.
Figure 1. Comparison of time of the stem-drying stages under different treatments.
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Processes 11 00726 g002 550
Figure 2. Comparison of economic characteristics of flue-cured tobacco leaves with different treatments.
Figure 2. Comparison of economic characteristics of flue-cured tobacco leaves with different treatments.
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Processes 11 00726 g003 550
Figure 3. Comparison of petroleum ether extracts of flue-cured tobacco after cured (%).
Figure 3. Comparison of petroleum ether extracts of flue-cured tobacco after cured (%).
Processes 11 00726 g003
Table
Table 1. Experimental design.
Table 1. Experimental design.
TreatmentsExperimental Design
CKThe maximum DBT is set to 68 °C during the SDS.
T1Based on CK, increase the DBT to 68 °C and stay for 2 h, then slowly increase to 72 °C at the rate of 1 °C/h until the main stem is dry.
T2Based on CK, increase the DBT to 68 °C and stay for 2 h, then slowly increase to 75 °C at the rate of 1 °C/h until the main stem is dry.
Table
Table 2. Comparison of curing energy consumption costs under different treatments.
Table 2. Comparison of curing energy consumption costs under different treatments.
TreatmentsCKT1T2
Total fresh tobacco (kg)4080.7 ± 42.80 b4205.8 ± 43.16 a4165.4 ± 35.14 a
Total dry tobacco (kg)541.6 ± 8.25 b581.3 ± 11.25 a552.8 ± 9.09 b
Coal consumption (kg)1074.7 ± 11.37 a992.3 ± 12.01 b965.7 ± 13.05 c
Electricity consumption (kWh)260.3 ± 8.02 a241.7 ± 3.51 b240.3 ± 2.52 b
Coal consumption per kilogram of dry tobacco (kg/kg)1.99 ± 0.01 a1.71 ± 0.01 c1.75 ± 0.01 b
Electricity consumption per kilogram of dry tobacco (kWh/kg)0.48 ± 0.008 a0.42 ± 0.003 c0.44 ± 0.003 b
Cost of coal consumption per kilogram of dry tobacco (USD/kg)0.64 ± 0.03 a0.55 ± 0.03 c0.56 ± 0.01 b
Cost of electricity consumption per kilogram of dry tobacco (USD/kg)0.06 ± 0.006 a0.05 ± 0.002 c0.05 ± 0.003 b
Total energy consumption per kilogram of dry tobacco (USD/kg)0.70 ± 0.02 a0.60 ± 0.03 c0.62 ± 0.02 b
Note: In 2021, the price of coal used in the BCB was 322.30 USD/t, and the local electricity price was 0.12 USD/kWh. The exchange rate was calculated according to the exchange rate of RMB to USD 1 = 0.1465 on 12 February 2023. Note: The letters (a, b, c) after the numbers in the same column indicate the test difference reached a significant level (p < 0.05), the same interpretation is used below.
Table
Table 3. Comparison of chemical composition of flue-cured tobacco after curing (%).
Table 3. Comparison of chemical composition of flue-cured tobacco after curing (%).
TreatmentTotal SugarReducing SugarNicotineK+Cl−Total Nitrogen
CK18.91 ± 0.12 c15.09 ± 0.40 c3.00 ± 0.04 a1.44 ± 0.02 a0.43 ± 0.02 a2.29 ± 0.11 a
T122.19 ± 0.69 a18.86 ± 0.72 a2.74 ± 0.06 b1.22 ± 0.05 b0.36 ± 0.15 b2.19 ± 0.14 b
T220.41 ± 0.79 b17.01 ± 0.52 b2.61 ± 0.03 b1.40 ± 0.02 a0.39 ± 0.25 ab2.12 ± 0.10 c
Table
Table 4. Comparison of sensory quality evaluation of flue-cured tobacco (score).
Table 4. Comparison of sensory quality evaluation of flue-cured tobacco (score).
TreatmentsAromatic QualityAromatic VolumeGaseous ConcentrationOffensive OdorStrengthIrritationAftertasteTotal Score
CK6.406.406.856.106.806.006.106.25
T16.506.506.806.306.606.306.306.40
T26.306.407.006.106.706.006.106.30
Table
Table 5. Comparison of appearance quality of tobacco leaves after different treatments.
Table 5. Comparison of appearance quality of tobacco leaves after different treatments.
TreatmentMaturityColorTarThicknessStructureTintSurface DustingGreen ContentAroma
CKMatureOrangeExist+Slightly thickSlightly denseConcentratedExistSlightly existExist+
T1MatureOrangeMuchModerateLooseConcentratedSlightly existNoneStrong
T2MatureOrangeExist+Slightly thickSlightly denseStrongExistNoneExist
Table
Table 6. Comparison of neutral aroma substances in cured tobacco leaves with different treatments (µg/g).
Table 6. Comparison of neutral aroma substances in cured tobacco leaves with different treatments (µg/g).
CategoryChemical NameTreatment
CKT1T2
Maillard reaction componentsFurfural19.6219.1719.34
Furfuryl alcohol2.473.512.92
5-methyl furfural2.993.263.18
3,4-Dimethyl-2,5-furandione0.860.920.97
2-acetyl pyrrole 2-acetyl pyrrole0.290.680.42
Aromatic amino acid cleavage substancesBenzylalcohol18.6620.6318.42
Benzaldehyde0.710.720.75
Phenylacetaldehyde5.906.826.99
Phenethyl alcohol7.478.238.03
Cembratriendid alkyl degrading productsSolanone34.9840.7137.02
Carotenoid degradation products6-Methyl-5-hepten-2-one 0.930.790.85
6-Methyl-5-hepten-2-ol 1.191.411.24
Linalool0.700.630.65
Isophorone0.320.340.31
Isophorone oxide0.140.170.21
β-Damascenone18.7621.3520.47
β-damascenone23.2527.9125.69
3-hydroxy-β-damascone2.532.862.44
Dihydroactinidiolide2.902.462.23
Geranylacetone2.332.041.97
Megastigmatrienone 11.962.442.05
Megastigmatrienone 210.7212.2811.84
Megastigmatrienone 35.725.385.07
Megastigmatrienone 414.2016.3115.37
Spirulina solavetivone1.522.011.74
β-Cyclocitral Beta-Cyclocitral1.011.000.99
Farnesyl acetone11.1513.2012.35
Other aroma constituents2,6-Nonadienal0.400.390.37
Adipaldehyde0.310.350.29
Guaiacol 2-Methoxyphenol2.112.342.28
NeophytadieneNeophytadiene862.261024.01946.84
Total contents (exception of Neophytadiene)196.10220.31209.41
Total total contents1058.361244.321156.25
Table
Table 7. The quantitative relationship between temperature during the stem-drying stage and inherent quality indexes of flue-cured tobacco after curing.
Table 7. The quantitative relationship between temperature during the stem-drying stage and inherent quality indexes of flue-cured tobacco after curing.
Test IndexesThe Quantitative RelationshipR2 (p < 0.05)
Total sugarY1 = −1023.746 + 29.041 x − 0.202 x20.878
Reducing sugarY2 = −1141.964 + 32.194 x − 0.223 x20.919
NicotineY3 = 6.774 − 0.056 x 0.935
K+Y4 = 85.555 − 2.353 x + 0.016 x20.925
Cl−Y5 = 18.029 − 0.489 x + 0.003 x20.710
Total nitrogenY6 = 3.899 − 0.024 x0.330
Petroleum ether extractsY7 = −163.070 + 4.708 x − 0.033 x2 0.978
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Jia, J.; Zhang, M.; Zhao, J.; Wang, J.; He, F.; Wang, L. The Effects of Increasing the Dry-Bulb Temperature during the Stem-Drying Stage on the Quality of Upper Leaves of Flue-Cured Tobacco. Processes 2023, 11, 726. https://doi.org/10.3390/pr11030726

AMA Style

Jia J, Zhang M, Zhao J, Wang J, He F, Wang L. The Effects of Increasing the Dry-Bulb Temperature during the Stem-Drying Stage on the Quality of Upper Leaves of Flue-Cured Tobacco. Processes. 2023; 11(3):726. https://doi.org/10.3390/pr11030726

Chicago/Turabian Style

Jia, Jingxiao, Mingjin Zhang, Jinchao Zhao, Jian’an Wang, Fan He, and Lifang Wang. 2023. "The Effects of Increasing the Dry-Bulb Temperature during the Stem-Drying Stage on the Quality of Upper Leaves of Flue-Cured Tobacco" Processes 11, no. 3: 726. https://doi.org/10.3390/pr11030726

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