Comparison of NaOH/Urea Method with Sulfuric Acid Method for Determining Lignin Content in Tobacco

In order to compare the difference of NaOH/Urea (NU)method and sulfuric acid method in determining the lignin content in tobacco, the lignin content in the tobacco stems and leaves sampled from Guangdong, Sichuan, Hunan, Yunnan and Guizhou were determined by both methods, and the removal rate of interfering substances in pretreatment process and the changes of content and structure of lignin in acid hydrolysis process were compared. The results showed that: 1)The pretreatment of NU method was more efficient in removal of interfering substances. 2) Diluted sulfuric acid solution was applied for hydrolysis in NU method, it reduced the degradation of lignin in tobacco. Moreover, the UV absorbance at 325 nm was selected for the quantification of acid soluble lignin (ASL), it avoided the interference of protein and furfural and improved the accuracy and reproducibility of the determination result. 3)The acid insoluble lignin isolated by NU method featured lower oxidation degree and less structural change, hence better represented the true structural characteristics of lignin in tobacco. NU method is more suitable for determining the lignin content in tobacco than is sulfuric acid method.