Dynamic Changes Of Polyphenol Oxidase Activity And Main Chemical Components In Tobacco NC102 During Curing Process

Different parts and different maturity tobacco leaves have certain differences in dry matter accumulation and leaf tissue structure.During the curing process,the decomposition and transformation of the internal chemical components will also show different rules.There is a close relationship between the chemical composition of tobacco leaves and the quality of tobacco leaves.The level of its content and coordination are one of the criteria for judging the quality of tobacco leaves.In this experiment,NC102,the main flue-cured tobacco variety in Shandong,was used as the test material.The dynamic changes of the contents of major chemical constituents and polyphenol oxidase(PPO)activity in tobacco leaves with different maturity at different parts and the quality of tobacco leaves from NC 102 mid-maturing ripe tobacco leaves after curing under different curing techniques were studied.The results provide a theoretical basis for the improvement of NC102’s mature harvesting and curing process.The results of reseach indicate:During the whole curing process,the PPO activity in the middle leaves first increased and then decreased,and the PPO activity in the lower and upper leaves showed a change rule of decreasing first,then increasing then decreasing;The activity of PPO in the lower,middle and upper parts were all peaked around 46℃,and the activity of PPO in tobacco leaves disappeared after 54 °C.The activity of PPO in the middle leaves decreased with the increase of maturity,while that of the lower and upper leaves was opposite.The effect of different curing process on the quality of tobacco leaves NC102 was the best in medium temperature,and the chemical composition of tobacco leaves was moderate and the proportion was the most harmonious.Suitable curing process for flue-cured tobacco NC102: yellowing period,dry bulb and wet bulb temperature is 38℃/37℃,color-setting period,dry bulb and wet bulb temperature is 45℃/ 39℃,dry-veins period,dry bulb and wet bulb temperature is 54℃/41℃.During the curing process,the moisture content of tobacco leaves showed a dynamic trend of water loss in the yellowing period,low water loss,rapid dehydration in the fixing phase,rapid water loss,and low water loss in the dry gluten season."Slow-fast-slow" change characteristics.During the curing process,the moisture content of the lower tobacco leaves was the highest,followed by the middle tobacco leaves and the lowest leaves.The interval with the largest changes in the moisture content of the over-matured tobacco appeared earliest,followed by the ripening tobacco leaves,and the late ripening tobacco leaves were the lates.The change of starch and soluble total sugar content in the pre-curing period changed greatly,and did not change significantly in the late curing period.With the continuous decomposition of starch,the total soluble sugar content increased continuously,and the content of the two substances showed a clear relationship.The content of starch in the fresh tobacco leaves was relatively higher than that in the unripe tobacco leaves.During the curing process,the degradation rate of starch in the middle and over-ripened tobacco leaves was faster.The total soluble sugar content of tobacco leaves after curing had a significant difference among different maturity levels.The content of tobacco leaf and under-ripe tobacco leaves in the upper part was the highest.The content of protein in fresh tobacco leaves and roasted leaves was the highest in the upper and lower mature tobacco leaves.During the curing process,the protein content changes greatly in the early period and the content in the later period tends to be stable.The lower tobacco leaves are degraded in advance in the middle and upper leaves,and the under-matured tobacco leaves and the appropriate ripe tobacco leaves are degraded faster in the yellowing stage.The content of protein in the lower leaves of the tobacco leaves was higher than that of the lower leaves in the middle leaves,and there were significant differences among the different parts.The protein content of the over-matured tobacco leaves was significantly lower than that of the under-matured tobacco and the suitable ripe tobacco leaves.The difference between the latter two was not significant.Nicotine content in tobacco leaves is relatively low,between 2.0% and 3.0%.Before and after curing,the contents of nicotine were highest in the upper leaves and under ripe leaves,and the contents of the lower leaves and over-matured leaves were the lowest,and there were significant differences between different maturity levels at different parts.During the curing process,the nicotine degradation rate in the early period of curing was slightly higher than that in the late curing period,and the overall change trend was relatively flat.