Research on the relative humidity changes of the controlled atmosphere environment for redried tobacco storage

Abstract

To study the ambient relative humidity changes during the controlled atmosphere alcoholization for redried tobacco storage. Firstly the critical factors of relative humidity of the controlled atmosphere for no tobacco and redried tobacco were researched, respectively. Then the models had been constructed and validated. The results showed that the relative humidity of the controlled atmosphere environment for no tobacco had significant correlation with nitrogen volume concentration and temperature, had insignificant correlation with oxygen volume concentration. And the relative humidity of the controlled atmosphere environment for redried tobacco had significant correlation with the nitrogen volume concentration, temperature, and moisture content of redried tobacco, and the interactions between the other factors were significant except for the interaction between the temperature and the nitrogen volume concentration, which was not significant. The relative errors of the relative humidity of the controlled atmosphere environment for no tobacco and redried tobacco were within 8% and 4%, respectively. Therefore quantitatively analyze and predict the relative humidity changes of the controlled atmosphere environment for redried tobacco storage with models to determine whether it meets the alcoholization quality of redried tobacco based on the equilibrium relative humidity of the redried tobacco storage through regulating the relative humidity of the controlled atmosphere environment. It can control precisely the alcoholization process and accelerate the alcoholization quality promotion of tobacco.

Introduction

The essence of tobacco alcoholization is to convert the unfavorable quality components in tobacco leaves into favorable ones through continuous biochemical reactions under specific environmental conditions, which must be carried out in order to make the tobacco quality meet the requirements of the cigarette industry^{1, 2–3}. There are two methods of tobacco alcoholization, natural alcoholization and artificial alcoholization⁴. Natural alcoholization method refers to the quality alcoholization of tobacco leaves under natural storage conditions, but hidden dangers such as mold and insects and uncontrollable factors exist⁵. Artificial alcoholization method refers to accelerate the alcoholization process of tobacco and improve their quality through controlling temperature, humidity, oxygen, carbon dioxide and nitrogen and other factors. Controlled atmosphere alcoholization has become the better choice for artificial curing and alcoholization of tobacco.

During the controlled atmosphere alcoholization process, environmental relative humidity is one of the key factors affecting the transformation of tobacco leaf intrinsic components⁶. Song Jizhen et al. showed that an air relative humidity environment of 55% to 65% was more conducive to the improvement of tobacco leaf alcoholization quality⁷. The appearance quality, physical properties and smoking quality of tobacco leaves could be greatly improved under appropriate conditions. While the tobacco leaves might become moldy and deteriorate with high humidity, affecting their quality⁸. However the tobacco leaves might become dry and brittle with low humidity, which was not conducive to alcoholization. Therefore, studying the relative humidity changes of the controlled atmosphere environment is of great significance to promote the tobacco storage. Controlled atmosphere alcoholization is usually carried out by placing a impermeable film over the tobacco box or the stack to ensure that the sealing meets the requirements of controlled atmosphere alcoholization⁹. Zhang Xin et al. found that controlled the atmosphere film was moisture -proof, and the relative humidity inside the film was almost unaffected by the humidity of the external environment¹⁰. Therefore, it is feasible to study the relative humidity changes of the controlled atmosphere environment for redried tobacco under the condition of the controlled atmosphere.

Literature showed that the relative humidity of the controlled atmosphere environment was related to the nitrogen gas concentration. Yang also indicated that the humidity of nitrogen was related to its purity¹¹. And the relative humidity of the controlled atmosphere environment is also related to the moisture content of the tobacco leaves. Because tobacco leaves are a material with hygroscopic and desorption characteristics, their moisture content is closely related to the relative humidity of the storage environment. The moisture content of tobacco leaves has a significant impact on their storage security and quality. When the moisture content is too high, the tobacco leaves in the lower layers of the stack are prone to oil leakage and agglomeration, and mold can grow, resulting in reduced tobacco quality. While the moisture content is too low, the tobacco leaves are not flexible enough and are prone to breakage during storage and processing, resulting in loss of tobacco raw materials¹². Yao had researched relative humidity change affecting flue-cured tobacco quality and conducted the relative humidity model to predict the moisture content of flue-cured tobacco. The model is:where X is relative humidity¹³. Therefore, the paper mainly explores the relative humidity changes of the controlled atmosphere environment for redried tobacco storage with key factors such as gas concentration of nitrogen and other gas, temperature, and the moisture content of redried tobacco.

Sun showed that the relative humidity detection method was to monitor data in real-time through the temperature & humidity sensor and to predict future humidity changes with experience¹⁴, which meant to regulate the relative humidity in the manner of “experience-based and instrumentation-assisted”. While there were few studies of regulating environment based on the ambient relative humidity model of controlled atmosphere alcoholization of redried tobacco storage. In the research a model to predict the relative humidity changes of controlled atmosphere environment and to regulate accordingly. The moisture content changes of tobacco leaves could be worked out through the relative humidity of controlled atmosphere environment for no tobacco and redried tobacco, then regulated the relative humidity of controlled atmosphere environment for no tobacco and redried tobacco based on the equilibrium relative humidity of tobacco leaves to make the ambient relative humidity conducive to the tobacco alcoholization quality promote.

Materials and methods

Experimental site and materials

This experiment was carried out in Changping Pilot Base of Academy of National Food and Strategic Reserves Administration, Changping District, Beijing, China, and the selected tobacco samples were tobacco strip-K326-C2F-G from 2022- Zhangjiajie Hunan Province, China.

Equipment and materials

Impermeable film bag (length × width × thickness = 65 mm × 45 mm × 8 mm, produced by Beijing Yingfenglitai Science and Technology Co., Ltd.); hose (inner diameter-4 mm, outer diameter-6 mm, length-80 mm, produced by Beijing Kaijialeyuan Biotechnology Co., Ltd.); gas regulating valve (produced by Beijing Yingfenglitai Science and Technology Co., Ltd.); long tail clip (small, diameter × length = 30 mm × 18 mm, produced by Zhejiang Leiting Stationery Co., Ltd.); temperature and humidity gas monitor (carbon dioxide gas concentration range: 0 ~ 60%; produced by Shenzhen Keernuo Electronic Technology Co., Ltd.); gas cylinder (99.99% nitrogen, 40L, produced by Beijing Anxingtailong Gas Chemical Co., Ltd.); gas cylinder (99.99% carbon dioxide, 40L, produced by Beijing Anxingtailong Gas Chemical Co., Ltd.); gas cylinder (99.99% oxygen, 40L, produced by Beijing Anxingtailong Gas Chemical Co., Ltd.).

Based on the requirements of YC/T 322–2018 Technical specification for storage and conservation of strips by controlled atmosphere method15, the main performance parameters of 8 mm thickness impermeable film are moisture permeability less than 0.5 g/(m²·h), oxygen permeability less than 80 cm³/(m²·24 h·0.1 Mpa). And its oxygen absorption range and carbon dioxide absorption range are 110 ~ 154 mL/g and 6 ~ 10 mL/g, respectively.

According to GB/T 1038.1–2022 Plastics-Film and sheeting-Determination of gas transmission rate-Part 1:

Differential pressure methods16, the main performance parameters of 8 mm thickness impermeable film selected in the experiment had been tested in Table 1. The result showed the 8 mm thickness impermeable film selected in the experiment could be the requirements of of air tightness related standard. Therefore in the periods of the experiment, the gas concentration of the 8 mm thickness impermeable film could be sustained at least 7d to meet the test duration.

Table 1. The main performance parameters of 8 mm thickness impermeable film.

Parameters/ Unite	Standard requirements	Test value
Moisture permeability (g/(m2·h))	≤ 0.5	0.15
oxygen permeability (cm3/(m2·24 h·0.1 Mpa))	≤ 80	31.7
oxygen absorption (mL/g)	110 ~ 154	113
carbon dioxide absorption (mL/g)	6 ~ 10	6

As can be seen from Fig. 1, firstly a hole of inner diameter 8 mm in 65 mm × 45 mm side of impermeable film bag, the hose was 2 mm deep into the sealed hole. Then the wireless temperature and humidity gas monitor was put into the impermeable film bag. Secondly the impermeable film bag was sealed. Finally the hose was linked to the gas control valve, and the gas control valve was linked to the gas cylinder with different experiment requirements.

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Fig. 1

Equipment installation and use diagram.

Experimental method

Orthogonal test of relative humidity of the controlled atmosphere environment for no tobacco

A preliminary test was carried out to explore whether the volume concentration of nitrogen, oxygen and carbon dioxide have any effect on the relative humidity of the controlled atmosphere environment for no tobacco. The results showed that there was a significant correlation between the volume concentration of nitrogen and the relative humidity of the controlled atmosphere environment, while there was no significant correlation between the volume concentration of carbon dioxide and the relative humidity of the controlled atmosphere environment.

Based on the preliminary test, orthogonal test was carried out with the volume concentration of nitrogen, temperature and volume concentration of oxygen as independent variables and the relative humidity of the controlled atmosphere environment as the dependent variable. Impermeable film bags with the thickness of 8 mm were selected according to YC/T 322–2018 Technical specification for storage and conservation of strips by controlled atmosphere method and a test was carried out to verify their air tightness.

The sampling results showed that the air tightness of this kind of impermeable film bags met the experimental requirements, and the qualified rate was above 95%. During the orthogonal test, a temperature and humidity gas monitor was placed into each sealed impermeable film bag, which was filled with gas according to the requirements of Table 2. Then all impermeable film bags were placed in a constant temperature environment of 20.00 °C, 25.00 °C, and 30.00 °C, respectively. All monitors were set to collect and record data every 4 h until the ambient relative humidity changed by no more than ± 0.1%, and maintained for 1 to 2 days. Nine groups of tests were carried out and each test repeated twice, for a total of 18 groups. Recorded the experimental data after the ambient relative humidity stabilized so as to analyze, build model and verify.

Table 2. Factor levels of orthogonal test.

Level	Nitrogen volume concentration (%)	Oxygen volume concentration (%)	Temperature (°C)
1	50.00	0.00	20.00
2	75.00	10.00	25.00
3	99.99	21.00	30.00

Response surface experiment of relative humidity of the controlled atmosphere environment for redried tobacco

Response surface experiment was conducted by taking nitrogen gas volume concentration, temperature, and moisture content of redried tobacco as independent variables, and relative humidity of controlled atmosphere environment as the dependent variable (as shown in Table 3). During the experiment, 900 g ± 10 g of redried tobacco were weighed and placed into the above-mentioned impermeable film bags, which with a temperature and humidity gas monitor inside. Then the sealed impermeable film bags were filled with gas according to the factor levels in Table 4, and placed in a constant ambient temperature of 20.00 °C, 25.00 °C and 30.00 °C, respectively. The monitoring method was described above monitor detecting method. A total of 17 groups of experiments were carried out and repeated once. Recorded the experimental data after the ambient relative humidity stabilized so as to analyze, build model and verify.

Table 3. Factor levels of response surface experiment.

Factor	Encoded value	Level
		− 1	0	1
Nitrogen volume concentration (%)	A	50.00	70.00	99.99
Temperature (°C)	B	20.00	25.00	30.00
Moisture content of tobacco (%)	C	10.00	11.75	13.50

Table 4. Experimental design and results.

Experimental treatment	A-nitrogen volume concentration (%)	B-oxygen volume concentration (%)	C-temperature ( °C)	Blank column	Relative humidity y1 (%)	Relative humidity y2 (%)
1	1 (50)	1 (0)	1 (20)	1	38.70	40.40
2	1	2 (10)	2 (25)	2	25.30	28.80
3	1	3 (21)	3 (30)	3	49.40	51.00
4	2 (70)	1	2	3	27.10	28.00
5	2	2	3	1	54.60	56.20
6	2	3	1	2	44.70	45.40
7	3 (99.99)	1	3	2	55.30	55.40
8	3	1	1	3	46.30	41.60
9	3	1	2	1	42.10	35.40
T1	113.40	209.50	129.70	135.40	T = 383.5	T = 382.2
T2	126.40	79.90	94.50	125.30
T3	143.70	94.10	159.30	122.80
R	10.10	7.10	21.60	4.20

When the nitrogen volume concentration was ≥ 99.99%, the oxygen volume concentration was replaced by level 1, which meant the oxygen volume concentration = 0%. When the nitrogen volume concentration + oxygen volume concentration was ≤ 99.99%, adopted CO₂ to make up. (Preliminary experiment showed no significant correlation between CO₂ volume concentration and relative humidity of the controlled atmosphere environment).

The previous research results and relevant literature^{17, 18, 19–20} showed that the suitable parameters for the controlled atmosphere alcoholization environment of redried tobacco were as below, temperature of (27 ± 1) °C and moisture content of 11% ~ 13%. Therefor the factor levels of response surface experiment were set as follows, temperature range of 20.00 °C ~ 30.00 °C and moisture content range of redried tobacco of 10.00% ~ 13.50%. And the nitrogen volume concentration was set as 50% ~ 99.99% because the practical application of high nitrogen volume concentration was of great significance in the controlled atmosphere alcoholization process of redried tobacco. According to the principle of Box-Behnken’s central combination experimental design, the response surface method was adopted to design a three-factor and three-level central combination response surface experiment for nitrogen volume concentration (A), temperature (B), and moisture content of redried tobacco (C). The relative humidity of controlled atmosphere environment for redried tobacco (Y₂) was taken as the evaluation index, and the levels of the individual factors were set and coded as shown in Table 3.

Result

Orthogonal test of relative humidity of the controlled atmosphere environment for non-redried tobacco

The range analysis (R) in Table 4 showed that the influence weights of the three factors on the relative humidity of the controlled atmosphere environment for no tobacco were temperature > nitrogen volume concentration > oxygen volume concentration.

The variance analysis was performed by using SPSS Statistics software (version, 29.0, SPSS Inc., Chicago, IL, USA). The experimental results, shown in Table 5, showed that there was a significant difference in the influences of nitrogen volume concentration and temperature on the relative humidity of the controlled atmosphere environment, while no significant difference in the that of oxygen volume concentration.

Table 5. Variance analysis.

Sources of variation	SS	DoF	MS	F value	P value	Significance
Nitrogen volume concentration (%)	160.99	2	80.49	7.65	0.01	*
Oxygen volume concentration (%)	22.08	2	11.04	1.05	0.98
Temperature (°C)	1145.88	2	572.94	54.46	< 0.001	*
Experimental error	115.74	11	10.52
Sum	1813.94	17

*Indicates that the significance level of 0.05 is reached.

Modeling

The relative humidity model of the controlled atmosphere environment for no tobacco was built with MATLAB and significance influencing factors selected referring to Table 5, as shown below,

1

where: A—nitrogen volume concentration/%, B—temperature/ °C.

As can be seen from Fig. 2, within the temperature range of 20 °C ~ 30 °C, the relative humidity of the controlled atmosphere environment for no tobacco first decreased and then increased with the increase of temperature. The speculation was that the saturated humidity of the controlled atmosphere environment increased at temperature range of 20 °C ~ 25 °C, and the relative humidity of the controlled atmosphere environment decreased under the condition of constant absolute humidity; due to the interaction between nitrogen molecules and water molecules. When the temperature increased to 25 °C ~ 30 °C, the interaction between nitrogen molecules and water molecules weakened, so the average kinetic energy of water molecules increased, causing more water molecules evaporated into the environment, which resulted in the increase of relative humidity of the controlled atmosphere environmen²⁰. The ambient relative humidity increased with the increase of nitrogen volume concentration under certain temperature. It’s speculated that the number of nitrogen molecules increased when the nitrogen volume concentration was high, and the number of water vapor molecules that interact with nitrogen molecules also increased, causing the relative humidity of nitrogen to increase.

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Fig. 2

Relative humidity model of the controlled atmosphere environment for no tobacco.

Model validation

The model was validated by laboratory data and the relative error was calculated. The experimental results, shown in Table 6, the absolute value of the relative error of the relative humidity of the controlled atmosphere environment for no tobacco was within 8%, and the model was relatively accurate to meet the requirements of real application.

Table 6. Comparison between the actual and predicted values.

No	Nitrogen volume concentration (%)	Temperature ( °C)	Actual value (%)	Predicted value (%)	Relative error (%)
1	77.00	20.00	40.70	41.02	0.79
2	80.00	25.00	29.90	28.11	− 5.99
3	85.00	25.00	30.80	28.74	− 6.69
4	85.00	25.00	30.50	28.74	− 5.77
5	73.00	25.00	29.10	27.24	− 6.39
6	73.00	25.00	28.90	27.24	− 5.74
7	99.99	30.00	49.80	53.53	7.49
8	75.00	30.00	47.70	50.32	5.49
9	85.00	30.00	50.30	51.58	2.54
10	85.00	30.00	51.60	51.58	− 0.04
11	80.00	30.00	49.30	50.94	3.33

Result analysis of response surface experiment

Response surface experiment results for relative humidity of the environment with controlled atmosphere of redried tobacco leaves

The regression model was established with Design Expert software (version 8.0.6, Stat-Ease, Beijing, China) to carry out variance analysis based on the experimental data. The significance of the differences among each factor was compared by P value and the results were shown in Tables 7 and 8.

Table 7. Box-Behnken test results of relative humidity of the controlled atmosphere environment with tobacco.

No	A-nitrogen volume concentration (%)	B-temperature ( °C)	C-Moisture content of redried tobacco (%)	D-humidity (%)
1	50.00	20.00	11.75	55.45
2	74.50	20.00	13.50	62.66
3	74.50	30.00	10.00	51.97
4	74.50	25.00	11.75	57.30
5	74.50	25.00	11.75	58.20
6	99.00	20.00	11.75	60.45
7	74.50	30.00	13.50	65.28
8	50.00	25.00	10.00	51.53
9	99.00	25.00	13.50	67.90
10	74.50	25.00	11.75	57.55
11	50.00	25.00	13.50	61.19
12	74.50	25.00	11.75	58.05
13	74.50	20.00	10.00	53.63
14	74.50	25.00	11.75	57.60
15	50.00	30.00	11.75	55.78
16	99.00	25.00	10.00	55.64
17	99.00	30.00	11.75	62.22

Table 8. Variance analysis of response surface regression equation.

Sources of variance	SS	DoF	MS	F value	D-Humidity (%)	Significance
Model	318.73	9	35.41	313.97	< 0.0001	**
A-nitrogen	61.94	1	61.94	549.13	< 0.0001	**
B-temperature	1.17	1	1.17	10.38	0.0146	*
C-moisture content	244.87	1	244.87	2170.96	< 0.0001	**
AB	0.52	1	0.52	4.6	0.0692	NS
AC	1.69	1	1.69	14.98	0.0061	**
BC	4.58	1	4.58	40.6	0.0004	**
A2	2.11	1	2.11	18.69	0.0035	**
B2	0.00318	1	0.00318	0.028	0.8713	NS
C2	1.61	1	1.61	14.23	0.007	**
Residual	0.79	7	0.11
Lack of fit	0.23	3	0.078	0.56	0.671	NS
Pure error	0.56	4	0.14
Total deviation	319.52	16

**indicates highly significant difference (P < 0.01), * indicates significant difference (P < 0.05). R² = 0.9980, corrected R² = 0.9955.

As shown in Table 8, the P value of this model was less than 0.001 (P < 0.001), which meant that its relationship with the response value was highly significant. The coefficient of determination R² = 0.9980, corrected R² = 0.9955, indicated that the model can explain 99.55% of the response value changes. The fit was accurate; the lack of fit value P = 0.671, which meant that the difference was insignificant (P > 0.05). This model was relatively stable with a small error, and suitable for the prediction of the response values of the above-mentioned independent variables within a certain range. The analysis showed that the influence weights of three factors on the relative humidity of the controlled atmosphere environment for redried tobacco storage were moisture content of redried tobacco > nitrogen volume concentration > temperature. And all the three factors had significant influences on the relative humidity of the controlled atmosphere environment for redried tobacco storage. The interaction between nitrogen volume concentration and moisture content of redried tobacco, and the interaction between temperature and moisture content of redried tobacco had highly significant effects on the relative humidity of the controlled atmosphere environment for redried tobacco storage; while the effect of the interaction between nitrogen volume concentration and temperature on the above-mentioned relative humidity was not significant. The regression model obtained by fitting the experimental results was as follows:

2

where: A—nitrogen volume concentration/%, B—temperature/°C, C—moisture content of redried tobacco/%.

Analyze the interaction of various factors by response surface method. The effect of the interaction between nitrogen volume concentration and moisture content of redried tobacco on the relative humidity of the controlled atmosphere environment. As shown in Fig. 3, when the nitrogen volume concentration was constant, the relative humidity in the controlled atmosphere environment increased with the increase of moisture content of redried tobacco, which was more significant with high nitrogen volume concentration. When the moisture content of redried tobacco was constant, the relative humidity in the controlled atmosphere environment increased with the increase of nitrogen concentration, especially with higher moisture. Tobacco are a kind of biomass capillary porous material, which can desorption and adsorption with the external environment. The experiment showed that when the temperature and nitrogen volume concentration were constant, evaporation process (desorption) would occur if the partial pressure of the vapor on the surface of the tobacco was greater than that in the controlled atmosphere environment. Higher moisture content of tobacco meant stronger desorption effect, resulting in the increase of the absolute humidity and then the increase of relative humidity of the controlled atmosphere environment for redried tobacco. Under the same moisture content of redried tobacco and high nitrogen conditions, the higher the nitrogen volume concentration, the higher the relative humidity of the controlled atmosphere environment for redried tobacco. This result was consistent with the changes of the nitrogen volume concentration’s effect on the relative humidity of the controlled atmosphere environment for no tobacco.

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Fig. 3

Effects of nitrogen volume concentration and moisture content of tobacco on ambient relative humidity. (a) Response surface; (b) Contour map.

Response surface and contour map of the interaction between temperature and moisture content of redried tobacco

As can be seen from Fig. 4, when the temperature was constant, the relative humidity of the controlled atmosphere environment for redried tobacco increased as the moisture content of redried tobacco increased, which was more significant under high temperature conditions. When the moisture content of the tobacco was constant, the above-mentioned relative humidity increased as the temperature increased, which was more significant under high moisture content of tobacco.

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Fig. 4

Effects of temperature and moisture content of tobacco on ambient relative humidity. (a) Response surface; (b) Contour map.

At the same temperature, the relative humidity of the controlled atmosphere environment for redried tobacco increased with the increase of moisture content of tobacco. Under the condition of low moisture content of tobacco, its ambient relative humidity didn’t change significantly with temperature, which might because the difference of temperature gradient from 20.00 °C to 30.00 °C was not large, resulting in insufficient evaporation of low-moisture tobacco leaves. However the temperature range of 20.00 °C to 30.00 °C was of strong significance in the application for the alcoholization process of redried tobacco storage. When the moisture content of tobacco was high, the relative humidity of the controlled atmosphere environment for redried tobacco increased with the increase of temperature. This might because the increase in temperature caused the average energy of the water molecules in the samples to increase, the evaporation rate to increase, the amount of water vapor in the controlled atmosphere environment to increase, leading to the increase of relative humidity of controlled atmosphere environment for tobacco.

Validation of relative humidity model of the controlled atmosphere environment for redried tobacco

As shown in Table 9, the model was validated by experimental data and the relative error was calculated. The absolute value of the relative error of the relative humidity in the controlled atmosphere environment for redried tobacco storage was within 4%, and the value calculated by model was relatively accurate to meet the requirements of real application.

Table 9. Comparison between the actual and predicted value.

No	Nitrogen volume concentration (%)	Temperature ( °C)	Moisture content of redried tobacco (%)	Actual value (%)	Predicted value (%)	Relative error (%)
1	99.99	30	12.0	62.00	62.86	1.39
2	50	25	12.0	58.90	58.00	− 1.53
3	50	30	13.5	61.20	62.65	2.37
4	75	20	12.0	60.20	58.09	− 3.50
5	75	25	13.5	64.70	63.96	− 1.14
6	75	30	10.0	53.40	52.21	− 2.23
7	99.99	20	13.5	67.50	66.80	− 1.04
8	99.99	25	10.0	56.10	55.81	− 0.52

Conclusions

The relative humidity of the controlled atmosphere environment for no tobacco had a significant correlation with the temperature and nitrogen volume concentration, and the influence weights were temperature > nitrogen volume concentration; while had no significant correlation with the oxygen volume concentration. Within the temperature range of 20.00 °C ~ 30.00 °C, the relative humidity of the controlled atmosphere environment first decreased and then increased. At the same temperature, the relative humidity of the controlled atmosphere environment increased as the nitrogen volume concentration increased. A prediction model was constructed with nitrogen volume concentration, temperature as independent variables and the relative humidity of the controlled atmosphere environment as dependent variable. The model relationship equation was:where A represented nitrogen volume concentration, %, and B represented temperature,  °C. After validated by experimental data, the value calculated by this model can meet the requirements of real application for its absolute value of the relative error was within 8%.The relative humidity of the controlled atmosphere environment for redried tobacco storage had significant correlation with the nitrogen volume concentration, temperature and the moisture content of redried tobacco. And the influence weights were moisture content of redried tobacco > nitrogen volume concentration > temperature; the interaction between nitrogen volume concentration and the moisture content of redried tobacco as well as the interaction between temperature and the moisture content of redried tobacco had highly significant correlation with relative humidity of the controlled atmosphere environment for redried tobacco, while the interaction between nitrogen volume concentration and temperature had insignificant correlation with the above-mentioned relative. The model relationship equation was:where A represented nitrogen volume concentration, %; B represented temperature, °C; and C represented the moisture content of tobacco, %. After validated by experimental data, the value calculated by relative humidity model of the controlled atmosphere environment for redried tobacco storage met the requirements of real application for its absolute value of the relative error was within 4%.

In the tobacco industry, the relative humidity of the controlled atmosphere environment has usually been regulated in a manner of “experience-based and instrumentation-assisted”. And there are few studies of regulating environment relative humidity on the basis of the ambient relative humidity model of controlled atmosphere alcoholization of redried tobacco storage. This research explored the relative humidity changes of the controlled atmosphere environment for redried tobacco storage, analyzed the above-mentioned relative humidity with constructed model to make prediction accordingly; and learned the relative humidity changes of the different moisture content of redried tobacco based on the equilibrium relative humidity of stored-tobacco to support the redried tobacco alcoholization quality requirements with dada model. However, in the paper one type of redried tobacco—K326 had been only researched, later other varieties of tobacco, such as G80, safflower and Dajinyuan, different thickness and different material of impermeable film will also be studied to further improve the relative humidity model of the controlled atmosphere environment in tobacco storage. And it can provide a more solid foundation for the practice of the controlled atmosphere for tobacco storage. Modified atmosphere technology indirectly controls the relative humidity (RH) of tobacco storage by regulating the gas concentration (such as O₂, CO₂ or N₂), which has broad application prospects. In terms of anti-mildew and quality improvement, the appropriate concentration of carbon dioxide and oxygen and the stabilization of RH at 55% ~ 65% have effective mildew risk and flue gas toughness; In the storage process, controlled atmosphere combined with humidity control can accelerate tobacco alcoholization, shorten the cycle and improve flavor consistency; In the redrying process, inert gas (such as N₂) is used to slow down water evaporation, which can optimize the relative humidity gradient and broken smoke rate. This technology is more environmentally friendly and accurate, and integrated with smart sensors to achieve dynamic control. It is expected to become a key technology in the intelligent storage and processing of the tobacco industry in the future.

Acknowledgements

This work was supported by the research facilities of China Tobacco Hunan Industrial Limited Liability Company and Academy of National Food and Strategic Reserves Administration, China.

Author contributions

D.F. Yin and J. Yin proposed the research program for environment relative humidity and developed equations. Y.Y. Zhu carried out the experiment. F. Xiao and Q.P. Fu carried out data analysis. L. Dai carried out detailed calculations. Y.B Qu, H. Zhang, Z.J. Zhang, W. Yin and T.T Fan participated in the overall research program on the development of environment relative humidity and made important contributions to the conceptualization of the framework of environment relative humidity.

Funding

“This research was funded by Research and Applied of Key Technologies for Dynamic Controlled Atmosphere of Carbon Dioxide and Oxygen for Tobacco Storage, grant number 110202202009 from China Tobacco Corporation”and “The APC was funded by Academy of National Food and Strategic Reserves Administration, grant number H23094”. Check carefully that the details given are accurate and use the standard spelling of funding agency names at www.nature.com/reprints.

Data availability

The datasets used and/or analyzed during the present study are available from the corresponding author upon reasonable request. All data generated or analyzed during this study are included in this published article.

Declarations

Competing interests

The authors declare no competing interests.

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Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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