Changes of granule structure and enzyme hydrolysability of starch in upper flue-cured tobacco leaves during bulk flue-curing | 密集烘烤过程中烤烟上部叶淀粉颗粒结构与酶解力变化

Chinese. [目的]探讨密集烘烤过程中烤烟上部叶淀粉颗粒结构、特性和相关酶活性的变化，为合理调控上部烟叶淀粉含量、提高上部叶质量提供理论依据。[方法]采用常规理化分析和扫描电子显微镜研究烘烤过程中上部烟叶淀粉酶活性、酶解力与颗粒结构的变化规律。[结果]烘烤过程中，烟叶中淀粉含量变化主要在变黄期，淀粉酶活性呈双峰曲线变化。淀粉颗粒的扫描电镜观察表明,鲜烟叶中淀粉颗粒主要为圆球形和长圆柱状，个别呈不规则形状，颗粒表面有明显的凹槽内陷和层状结构；烘烤过程中，变黄期大量淀粉颗粒表面出现层状结构，长圆柱状淀粉颗粒大量减少；烘烤结束，烤后烟叶中几乎没有长圆柱状淀粉颗粒。鲜烟叶颗粒长轴平均粒径为3.21 μm；烘烤过程中淀粉颗粒长轴平均粒径整体上呈逐渐增大的趋势，38和42 ℃增加明显，42 ℃结束淀粉颗粒粒径增幅60%以上，47 ℃以后变化差异不明显。烟叶中淀粉的酶解力在烘烤过程中的变化是先增大，在38 ℃时达到峰值，然后降低。[结论]密集烘烤过程中变黄期是烤烟淀粉降解、颗粒结构、特性变化的关键时期，通过调控变黄期的烘烤环境条件对改善上部烟叶质量具有积极的作用。

English. [Objective] This study aimed to investigate the changes of granule structure, characteristic and related enzymatic activity of starch in upper flue-cured tobacco leaves during bulk flue-curing process, to provide theoretical basis for reasonably regulating the starch content in upper flue-cured tobacco leaves and improving the quality of upper flue-cured tobacco leaves. [Method] Changes of amylase activity, enzyme hydrolysability and granule structure of starch in upper flue-cured tobacco leaves were studied during flue-curing process using conventional physical and chemical analysis and SEM. [Result] During the flue-curing process, the starch content of tobacco leaves changed greatly at yellowing stage, and the activity of amylase presented the double-peak curve. The SEM observation results showed that most of the starch granules in fresh tobacco leaves were spheroidal and long cylindrical, while some individuals were in irregular shape, with obvious groove-like invagination and layered structure on granule surface; during the flue-curing process, a large amount of starch granules showed layered structure on the surface at yellowing stage, and the long cylindrical starch granules were reduced greatly; at the end of flue-curing, there were barely any long cylindrical starch granule in flue-cured tobacco leaves. Average long- axis-diameter of starch granules in fresh tobacco leaves was 3.21 um, showing an overall gradually increasing trend during the flue-curing process, which was significantly enhanced at 38 and 42 ℃. The diameter of starch granules increased by more than 60% at the end of 42 ℃ and there was no remarkable difference after 47 ℃. During the flue-curing process, enzyme hydrolysability of starch in flue-cured tobacco leaves first increased, reached a peak at 38 ℃, and then decreased. [Conclusion] During the bulk flue-curing, the yellowing stage is the critical period for starch content, granule structure and characteristic changes of flue-cured tobacco leaves, it is of positive effects to improve the quality of upper flue-cured tobacco leaves by regulating the flue-curing conditions at yellowing stage.