Correlations between Quality Index and Content of Cellulose and Lignin in Upper Leaves of Fluecured Tobacco in Wulin Mountain Area

Xiaobing LIU,Lin MENG,Meng LIANG,Chengdong WANG,Wenjing SONG,jiaobao ZHENG，Yimin XU*.Tobacco Research Institute,Chinese Academy of Agricultural Sciences,Qingdao 2660,China;2.Graduate School of Chinese Academy of Agricultural Sciences,Beijing 0008,China .Shandong Laiwu Tobacco Company,Laiwu 2700,China

Cell wall is the framework of plant and plays supporting and protection functions for plant tissues and organs.Cell wall is consisted of cellulose,lignin,hemicellulose,pectin substance and other inert matters.Cellulose isD-glucose connected byβ-1,4 glucosidic bonds and the chain combines together through the longer axis to form micro fiber bundle,which has high stability and ability to resist chemical degradation.Lignin is not a sugar but a high-molecular polymer of phenol 3 d mesh type aggregated byp-coumarin alcohol,coniferyl alcohol and sinapinic alcohol.Lignin mainly locates among cellulosic fiber and plays functions including compression resistance and improvement of the mechanical strength of tissue.Cell wall substance of fluecured tobacco leaf probably occupies 1/3 dry matter,which has bad effects on the frangrance and smoking taste of cigarette[1-2].Quality of tobacco leaf is bad when the contents of cellulose and lignin in flue-cured tobacco leaf are high.Low degree tobacco leaf contains higher cellulose and lignin and the smoke is bucking,astringent and has strong irritation,scorched gas and heavy wood gas,which affect the taste,harmony and safety of tobacco leaf[3-5].

Clearing the correlations among indexes of tobacco leaf quality and contents of cellulose and lignin has an important referential significance on the evaluation of tobacco leaf quality.Therefore,the aspect is widely concerned by many scholars.Chenet al.[6]analyzed and studied the correlations among cellulose content,lignin content,appearance quality and sensory quality.Renet al.[7]used partial correlation to analyze the correlations among cell wall substance,appearance quality,physical property and sensory quality.Yanet al.[8]studied the correlations among lignin,chemical component and physical property.Zhuet al.[9]studied cellulose variation and correlation between the variation and chemical component.There were a plenty of studies on the correlations among quality of tobacco leaf and content of cellulose and lignin in tobacco leaf,but the studies were restricted to the correlation between individual evaluation indexes of tobacco leaf quality and one or two of the contents of cellulose and lignin.Analysis on the correlations among cellulose content,lignin content and four quality indexes including appearance quality,physical property,chemicalcomponentand sensory quality has not been conducted.A total of 48 tobacco leaf samples in Wulin mountain area were harvested as test materials.The study aimed to provide a basis for the selection of quality index of tobacco leaf and improvement of industry usability of upper tobacco leaf according to the measurement of the contents of cellulose and lignin in tobacco leaf,and the correlations analysis among which and the four evaluation indexes of tobacco leaf.

Materials and Methods

Test materials

Wulin mountain area stretches in three provinces and one city including Yu,E,Xiang and Qian,and the length of which is about 420 km while the area of which is about 1 million km2.It locates at 27°10′-31°28′of northern latitude and 106°56′-111°49′of east longitude with an average altitude of about 1 000 m.Climate of the area belongs to the transitional type from subtropics to warm temperate zone and the annual average temperature is 13-16℃,and the amount of precipitation is 1 100-1 600 mm.Tobacco planting area in Wuling mountain is one of the typical ecological regions of Chinese flue-cured tobacco.Quality of the fluecured tobacco has typical characteristics of regional style.Forty eight samples of preliminarily baked tobacco leaf in Lichuan and Xianfeng of Hubei,Sangzhi and Fenghuang of Hunan,Dejiang and Daozhen of Guizhou and seven counties of Wulong,Chongqing were harvested in 2011-2012,and the sampling weight of each sample was 5 kg (Fig.1). ‘K326’, ‘Yunyan 87’,‘Yunyan 97’and ‘Nanjiang 3’ were the main cultivars in Wuling mountain area.

Test methods

Measurement of appearance qualityMethod introduced by Bao[10]was adopted in the study to evaluate the appearance quality of tobacco leaf.The determined indexes included maturity,color,oil content,status,structure and chroma.

Measurement of physical indexThe determined physical property indexes mainly included per leaf weigh(g),leaf density(g/m2),stem ratio(%),leaf length(cm),leaf width(cm),equilibrium moisture content(%),leaf thickness (μm)and filling value(cm3/g).Measurement of physical index was referred to the method provided by Bao[10].

Measurement of chemical componentMethod of YC/T347-2010 was used to measure the contents of cellulose and lignin.Method of YC/T159-2002 was used to measure the contents of total sugar and reducing sugar.Method of YC/T160-2002 was used to measure the total alkaloids content.Method of YC/T161-2002 was used to measure the total nitrogen content.Method of YC/T173-2002 was used to measure the kalium contentand method of YC/T162-2002 was used to measure the chlorine content.

Sensory quality assessmentSensory quality assessment of tobacco was conducted by Tobacco Quality Supervision,Inspection and Testing Center of the Ministry of Agriculture.The evaluation indexes included smoking aroma quality,amount of aroma,agreeable aftertaste,miscellaneous qi,irritation and grayness.The concrete assignment standard was referred to the method of Baoet al[10].

Data processing

SPSS19.0 software was used for variance analysis and simple correlation analysis.

Results and Analysis

Differential analysis on contents of cellulose and lignin

Differences of the contents of cellulose and lignin between yearsAnalysis results of the contents of cellulose and lignin between years were shown in Table 2.The average cellulose content of upper tobacco leaf sample in Wuling mountain area was 7.85%and the variation amplitude was 6.17%～10.06%,and the variable coefficient was 10.57%.The average value of lignin content was 2.20%and the variation amplitude was 1.10%-3.70%with a variable coefficient of 29.49%.The average value of cellulose content in 2012(8.05%)was higher than that in 2011 (7.73%)and the variable coefficient in 2012 was bigger than that in 2011 as well.The average value of lignin content in 2012(2.38%)was higher than that in 2011 (2.10%)while the variable coefficient in 2011 was bigger than that in 2012.The results of variance analysis indicated that differences of the contents of cellulose and lignin between years were not significant,which illustrated that contents of cellulose and lignin in tobacco leaf were quite stable and not easily affected by the fluctuation of climatic conditions and cultivated factors among years.

Differences of the contents of cellulose and lignin among varietiesAnalysis results of the contents of cellulose and lignin among varieties were shown in Table 3.The average cellulose content and lignin content of K326 were the highest while that of Nanjiang 3 were the lowest.The contents of cellulose and lignin ranked from high to low as follows:K326, ‘Yunyan 87’,‘Yunyan97’ and ‘Nanjiang 3’.Variation amplitude and variable coefficient of cellulose content of K326 were the biggest.Variation amplitude of cellulose content of ‘Yunyan 87’ was the biggest while the variable coefficient of‘Nanjiang 3’ was the biggest.The variation analysis results showed that differences of the contents of celluloseand lignin among varieties were not significant, which illustrated that though the samples were taken from different varieties,the contents of cellulose and lignin among varieties were stable.

Table 1 Detail information of the sample points

Differences of the contents of general chemical indexes among yearsVariation analysis results of the contents of general chemical indexes were shown in Table 4.It is generally acknowledged that general chemical indexes of flue-cured tobacco with good quality were as follows:the content range of reducing sugar is 16%-18%;thecontentrange of totalsugaris 18%-22%;the content range of total alkaloids is 2%-3%;the content range of total nitrogen is 1.5%-3.0%;kalium content is more than 2%while chlorine content is less than 1%.It could be seen from Table 4 that average values of the contents of reducing sugar and total alkaloids were slightly higher than that of the flue-cured tobacco with good quality.Variation amplitude and variable coefficient of Cl content were big while the variable coefficients of other general chemical indexes were small.The results of variation analysis indicated that contents of reducing sugar,total sugar,total nitrogen,K and Cl had no differences between years while the difference of total alkaloids content between years reached a significant level,which illustrated that total alkaloids content was easily affected by the fluctuation ofecological conditions between years while other general chemical indexes were more stable.

Correlations among indexes of appearance quality and the contents of cellulose and lignin

The results of correlation analysis on indexes of appearance quality and the contents of cellulose and lignin were shown in Table 5.Cellulose contents in 2011 and 2012 were extremely significantly positively and significantly positively correlated with the maturity,respectively.However,cellulose contents in 2011 and 2012 had a negative correlation and a significantly negative correlation with the oil content,respectively,while cellulose contents in 2011 and 2012 had no significant correlation with other indexes of appearance quality.Lignin contents in 2011and 2012 were negatively correlated and extremely significantly negatively correlated with the oil content while which had no significant correlation with otherindexesofappearance quality.The analysis indicated that cellulose and lignin had significant effects on oil content.The oil content in tobacco leaf is few and the tobacco leaf is easily broken when the contents of cellulose and lignin is high.

Table 2 Contents of cellulose and lignin in different years

Table 3 Contents of cellulose and lignin of different varieties

Table 4 Contents of general chemical indexes in different years

Correlations among physical property indexes and the contents of cellulose and lignin

The results of correlation analysis on physical property indexes and the contents of cellulose and lignin(Table 6)indicated that cellulose contents in 2011 and 2012 were significantly positively and positively correlated with per leafweight,respectively,and extremely significantly positively and positively correlated with stem ratio,respectively while which had no significant correlation with other physical property indexes,which indicated that per leaf weight and stem ratio would show an increasing tendency with the increasing of cellulose content.Lignin content had no significant correlation with the physical property indexes,which indicated that lignin content had a very slight effect on physical property indexes of tobacco leaf.

Correlations among general chemical indexes and the contents of cellulose and lignin

Correlation analysis on chemical indexes of tobacco leaf and the contents of cellulose and lignin (Table 7)showed that cellulose contents in 2011 and 2012 were extremely significantly negatively and significantly negatively correlated with the contents of reducing sugar and total sugar,respectively while that were extremely significantly positively correlated with total nitrogen content,and which were extremely significantly positively and positively correlated with the contents of total alkaloids,K and Cl,respectively.The differences of correlation coefficient of total alkaloids between years might be resulted from the significant differences of the contents of total alkaloids between years.The differences of correlation coefficient of Cl content might be resulted from its fluctuant contents.Lignin content had no significant correlation with the general chemical indexes.

Correlations among indexes of sensory quality and the contents of cellulose and lignin

The results of correlation analysis on indexes of sensory quality and the contents of cellulose and lignin(Table8)showed that cellulose contents in 2011 and 2012 were extremely significantly negatively correlated with smoking aroma quality,and negatively and extremely significantly negatively correlated with amount of aroma,respectively,and significantly negatively and negatively correlated with agreeable aftertaste and miscellaneous qi,respectively while that were significantly negatively correlated with irritation and total contents.The results indicated that with the increasing of cellulose content,smoking aroma quality and agreeable aftertaste were become bad;amount of aroma was decreased while miscellaneous qi was increased and irritation was strengthened;grayness was become dark and the whole sensory quality of tobacco leaf was decreased.Lignin contents in 2011 and 2012 were extremely significantly negatively and negatively correlated with the grayness,respectively and which were negatively correlated with smoking aroma quality,amount of aroma,agreeable aftertaste,miscellaneous qi,irritation and total content,and the negative correlations did not reach a significant level.The results indicated that the increasing of lignin content had a certain degree of bad effect on every index of sensory quality.It could be seen that decreasing of the contents of cellulose and lignin had an important effect on the improvement of tobacco leaf taste.

Table 5 Correlation coefficients between indexes of appearance qualities and contents of cellulose and lignin

Table 6 Correlation coefficients between indexes of physical properties and contents of cellulose and lignin

Discussions

Contents of cellulose and lignin of flue-cured tobacco are the consequences of genetic factor,ecological environment,cultivation techonique[11-12]and roasting technology[13].The study results showed that the cellulose content of upper tobacco leaf in Wuling mountain area was 6.17%-10.06%with an average value of 7.85%,and the variable coefficient was 10.57%.The lignin content was 1.10%-3.70%with an average value of 2.20%,and the variable coefficient was 29.49%.The content ranges of cellulose and lignin in the study were accorded with that in the study of Chenet al.[12].Contents of cellulose and lignin had no significant difference between years while the contents in 2012 were higher than that in 2011.Differences of the contents of cellulose and lignin among varieties were not significant,and the contents ranked from high to low as follows:‘K326’,‘Yunyan 87’,‘Yunyan 97’and ‘Nanjiang 3’.

Table 7 Correlation coefficients between main chemical contents and contents of cellulose and lignin

Table 8 Correlation coefficients between indexes of sensory quality and contents of cellulose and lignin

Cellulose and lignin has important influences on the quality of tobacco leaf[14].Cellulose content was positively correlated with the maturity,which was accorded with the study result of Chenet al.[6].With the increasing of tobacco maturity,reducing sugar,total sugar and starch were degraded while cellulose,lignin and other cell wall substances were slightly degraded,thus the relative percentage contents of cellulose and lignin in tobacco leaf were increased.Contents of cellulose and lignin were significantly negatively correlated with oil content.Cellulose and lignin are constitutionally stable,insoluble in water and general organic solvents,which made the tissue of tobacco leaf rough,oil content decreasing and the elasticity lessening.Therefore,the contents of cellulose and lignin in low-grade fluecured tobacco were high that the tobacco leaves were thin and easily broken with a few oil contents,bad hygroscopicity.

Cellulose content of tobacco leaf in 2011 was significantly positively correlated with per leaf weight and stem ratio and the correlation tendencies among which in 2012 were the same.The results indicated that with the increasing of cellulose content,per leaf weight and stem ratio were increased.Correlation between lignin content and every physical property index was not significant, which showed thatlignin contenthad a slightly effect on the physical property indexes.

Cellulose contents of tobacco leaf in 2011 and 2012 were extremely significantly negatively and significantly negatively correlated with the contents of reducing sugar and total sugar,respectively,while which were extremely significantly positively correlated with total nitrogen content,and which were extremely significantly positively and positively correlated with the contents of total alkaloids,K and Cl,respectively.The results were failed to agree with the study result of Zhuet al.[9].The measurement method used by Zhuet al.[9]was accorded with that by Renet al.[7].The cellulose content obtained by Zhuet al.was similar with and 7%-8%higher than that obtained by Renet al.The cellulose measured by Zhu might be holocellulos.Cellulose tester was used in this study for the accurately measurement of cellulose content[15].Therefore,correlation between cellulose content and each chemical index could be accurately analyzed.

High contents of cellulose and lignin in tobacco leaf resulted in strong irritation,spicy smoking taste,astringent taste and inadequate aroma[3-5].Cellulose contentwas significantly negatively correlated with each index of sensory quality and integrated score of smoking,which was accorded with the study result of Yanet al.[8].The results indicated that decreasing of cellulose contentcould increase the amount of aroma and make the smoking aroma quality better,agreeable aftertaste comfortable and pure,miscellaneous qiand irritation lightand grayness white,which is facilitate to improve the sensory quality of tobacco leaf.Lignin content was extremely significantly negatively correlated with the grayness in 2011 and negatively with other indexes of sensory quality but not significant.It could be seen that cellulose and lignin had bad effects on grayness while which had positive effects on the improvement of combustibility[16].However,combustibility usually had an opposite tendency with burning perfectibility.Research[17]had indicated that arbonization ability of cellulose was relatively weak.Therefore,high contents of cellulose and lignin go against with the burning perfectibility of tobacco leaf that the grayness tends to grey black.

Conclusions

Differences of the contents of cellulose and lignin in upper tobacco leaves in Wuling mountain area between years and among varieties were small.Cellulose and lignin were negative factors of the quality indexes of tobacco leaf.The negative effect of cellulose on sensory quality was especially significant.Therefore,cellulose and lignin of tobacco leaf were important factors that affect tobacco leaf quality.

In the production of tobacco leaf,effective measures should be adopted to decrease the contents of cellulose and lignin in upper tobacco leaf in order to improve the poor quality of upper tobacco leaf in China and low availability in industry.Currently,comprehensive and systematic study on content changes of cellulose and lignin during the baking process was lacking.In recent years,experimental study with enzyme degradation technology gained partial achievements[18,20].Because of the high cost and industrial operational problems,the technology has not been widely applied to industrial production.Therefore,planting area and cultivation technology need to be optimized to decrease the contents of cellulose and lignin in upper tobacco leaf and improve tobacco leaf quality,and increase the utilization efficiency of upper tobacco leaf.

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