Abstract
Japanese green tea is a highly processed product. The manufacturing process of Japanese
green tea consists of six steps which are followed by steaming, coarse kneading, crumpling,
secondary kneading, precise kneading and drying. Each step in the process is important to
increase the commercial quality of final tea products. However, few studies have focused
on the changes in green tea leaf properties during processing. This study aimed to examine
the effect of processing at each step on the structural attributes of Japanese green tea leaf.
The fresh tea leaves were harvested at experimental field of NARO in Shizuoka in 2017 and
continuously processed. The sample tea leaves were collected at each processing step and
immediately cooled in a refrigerator. The samples at each step were separately infused by
a distilled water at 100 °C for 30 s, and then removed from infusion and placed on a paper
towel for drying. A scanning electron microscope (SEM) was used to observe the surface
microstructures of sample tea leaves. The processed tea leaves were also infused by
a distilled water at 95°C for 5 min to examine the total polyphenol content (TPC),
ferric-reducing antioxidant power (FRAP) and free-radical scavenging assay (DPPH).
As a result, cracks and wrinkle-like structures on the surface of tea leaves were found and
increased with the processing step. TPC, FRAP, DPPH also increased with the processing. The
SEM image of tea leaves was also revealed that the surface microstructural changes possibly
connected with the TPC and antioxidant activity of green tea infusion. This should be
considered that the condition of each processing step could influence on not only the
apparent quality of final Japanese green tea product but also the functional properties of
green tea infusion.
