Influence and optimization of long-time superfine grinding on the physicochemical features of green tea powder

Superfine grinding is a crucial step in green tea powder (GTP) processing. In this work, the time-resolved changes of physicochemical properties (physical properties, main active components, etc.) of GTPs were investigated, and ball milling time (BMT) for tea grinding was optimized. Variable importance in projection was used to evaluate the importance of modification of each physicochemical parameter on BMT, and a multi-objective fuzzy optimization model was used to obtain the optimal BMT. The BMT range was 2–30 h, and the results showed that BMT had a significant influence on the physicochemical properties of GTP. The mean particle size decreased from 257 to 10.6 μm and the color became lighter as the BMT increased. The main active components decreased markedly when BMT increased form 18–24 h. Mean particle size and color difference dramatically correlated with BMT and could be described by a one-phase exponential decay function. The optimal BMT was 18 h and high quality GTP could be obtained under this condition with small particle size, bright green color and rich in theanine and total tea polyphenols (TTPs).