Abstract: In order to reduce pectin in tobacco stem， four factors including the amount of pectinase from Aspergillus niger SW06， liquid\|material ratio， temperature and time were optimized for the degradation process of tobacco stem by single factor and orthogonal experiment methods. The pyrolysis products of degraded tobacco stem was investigated by on\|line pyrolysis gas chromatography/mass spectrometry （PY/GC\|MS） prior to and after enzymolysis. The results showed that the maximum degradation rate of 34.82% was achieved with an enzyme activity of 29 000 U·mL-1， and a 1∶3 ratio of liquid to solid at 50℃ for 2 h. After enzymolysis， the composition and content of pyrolysis of tobacco stem changed obviously. Compared with the control， the alcohol flavor components increased from （5.25±0.03）% to（6.06±0.02）%. While， the acetic acid content decreased from （9.07±0.15）% to （8.31±0.12）%， The pungent and irritating taste also reduced， and N\|heterocycles， carbonyl compounds decreased by 0.11% and 1.20%， respectively. In general， the harmful compounds in smoke were reduced and smoke quality was improved.

Key words: pectin degradation, enzyme activity, degradation rate, pyrolysis