Changes in malic acid concentrations of tobacco leaves and the relative enzyme activities during the curing process

【Objective】 The change mechanism of malic acid concentrations and the relative enzyme activities in tobacco leaves during the curing process were analyzed in order to provide a theoretical basis for intensive study of chemical composition change and control mechanism during flue-curd process.【Method】 Research was conducted on the contrast of malic acid and total organic acid content and enzyme activities changes of MDH,PEPC and SDH in different flue-cured tobacco varieties such as K326,Yunyan 87 and Yuyan 6 at different stages(before curing,during curing at 38,42,48,54 ℃ and after curing) and the correlation between enzyme activity and malic acid and total organic acid content was analyzed.【Result】 The MDH,SDH and PEPC enzyme activities of different tobacco varieties showed some regularities.During the flue-cured process,the MDH activity increased first and then decreased and reached its peak at 48 ℃;the PEPC activity first rose and then declined and then rose again,as a whole,the degree of the activity had a ascend trend;the SDH activity steadily declined after 38 ℃ and reached its bottom at 54 ℃.During the curing process,malonic acid content had an up trend and reached its peak at 54℃.Malic acid and total organic acids contents of K326,yunyan 87 and yuyan 6 increased first and then decreased during the flue-cured process and reached its peak at 54,48 and 42 ℃ respectively.The result of correlation analysis showed that the MDH activity had no significant relation with the malic acid content in different flue-cured tobacco varieties;the PEPC activity had positive relation with the malic acid and total organic acid content in K326 and Yuyan 6 and had negative relation in Yunyan 87,and the correlation was not significant;the SDH activity had significant negative relation with the malic acid content in K326 and Yuyan 6 and not significant in Yunyan 87.【Conclusion】 The malic acid contents in different flue-cured tobacco varieties were obviously different.The effect on malic acid accumulation of SDH was bigger than that of MDH and PEPC.Relatively high MDH and PEPC activities and relatively low SDH activity could promote the accumulation of malic acid.