Effects of low temperature liquid nitrogen on quality of green tea grinding

In order to reduce the loss of thermal sensitive materials, a new method to grind green tea with low temperature liquid nitrogen was studied. Liquid nitrogen was added in the pulverizing green tea which as the research object in this study. The qualities of green tea pulverized by the liquid nitrogen pulverizing and conventional crushing method were compared. The results showed that, compared with the traditional crushing, the rate of powder pulverized with liquid nitrogen was higher and the qualities of color, taste and sense of the tea were higher. The hydrosoluble materials including the tea polyphenol, caffeine, the free amino acids, soluble protein, soluble sugar contents were respectively improved by 25.12%、10.12%、9.50%、6.75%、12.63%、9.05% after liquid nitrogen pulverizing. GC-MS analysis showed that the most aroma compositions of tea powder processed by the two kinds of crashing method were almost the same, but the contents of farnesene, nerolidol, 1H-indole、hexanoicacid-3-hexene ester, 2,2,4,4,6-Pentamethyl heptanes, amygdalin and 3-methyl butyric acid/2-methyl propyl ester were higher by 10.88%、13.70%、14.06%、5.61%、2.08%、24.39%、5.68% respectively for the liquid nitrogen pulverizing. This study results indicate that grinding with liquid nitrogen can maintain good quality of tea, and can provide a reference for green tea processing with liquid nitrogen pulverizing.