球磨法制备富硒绿茶粉工艺优化

以紫阳富硒茶成叶为原料,通过漂烫杀青、冷冻干燥和球磨等工艺制备富硒绿茶粉,在漂烫工艺中以茶叶成叶中硒元素含量为指标考察硒元素的流失情况,比较了冷冻干燥与40 ℃烘箱干燥的干燥效率,并选择球磨时间、研磨球大小球比和球磨转速三个因素,通过单因素和正交试验对制备工艺条件进行优化。实验结果表明,漂烫温度为100 ℃条件下,茶叶成叶中硒含量随漂烫时间延长而降低,由69.58 μg/kg(0 s)降低至64.72 μg/kg(60 s),损失率7%;16 h冷冻干燥鲜叶失水率为52.05%,40 ℃烘箱干燥失水率为49.52%。影响富硒绿茶粉颗粒粒径大小的因素依次为球磨时间>大小球比>球磨转速,球磨加工最优工艺为:球磨时间50 min,球磨转速800 r/min,大小球比1:6;采用激光粒度仪及扫描电镜对其表征,球磨颗粒形态断面清晰,粒径分布均匀,D₅₀值为3.25±0.35 μm,茶粉中硒含量为(63.18±4.22) μg/kg。该工艺条件下生产的富硒绿茶粉颗粒均匀,色泽翠绿,茶叶中硒元素保留度高。

Optimization of Preparation Technology for Selenium-Rich Green Tea Powder with a Ball-Grinding Method

Selenium-enriched green tea powder was prepared with Ziyang selenium-rich tea leaves as raw materials by blanching,freeze-drying and ball-grinding methods. The loss rate of selenium in this process was investigated,and the efficiencies of lyophilization and oven drying at 40 ℃ were compared. Grinding time,ratio of big to small ball,and rotation speed were chosen as factors,single factor and optimal orthogonal experiments were adopted to optimize the whole process. Base on the results,the amount of selenium within leaf was decreasing as time under 100 ℃,the loss rate was 7% as the weight changed from 69.58 μg/kg at 0 s to 64.72 μg/kg at 60 s. After 16 h,the water loss rate values were 52.05% in lyophilization and 49.52% at 40 ℃ by oven drying. The factors affecting particle size were following this order:grinding time>ratio of big to small balls>rotational speed. The results showed the optimal parameters of the ball-grinding method were as follows:grinding time 50 min,rotational speed 800 r/min,and ratio of big to small ball:1:6. Laser particle size analyzer and scanning electron microscope were empolyed to characterize the size and shape of the tea powder. The results indicated the morphology of ball milling particles’section was clear,particle size distribution was uniform,D₅₀ was 3.25 μm,and the selenium content in tea powder was(63.18±4.22) μg/kg. In the process condition,the selenium-enriched green tea powder had uniform granules,bright green color and high retention of selenium.