[4-1600-A] Postharvest/Food Technology and Process Engineering (3)

[4-1600-A-06] Effect of Processing Conditions on Bioactive Compounds and Antioxidant Activities of Tea Infusion

*Wei Qin¹, Sunantha Ketnawa¹, Florencio, Jr. Collado Reginio^1,2, Ryutaro Yamada³, Takuya Araki³, Yukiharu Ogawa¹ (1. Graduate School of Horticulture, Chiba University.(Japan), 2. Institute of Food Science and Technology, College of Agriculture and Food Science, University of the Philippines Los Baños(Philippines), 3. Institute of Fruit Tree and Tea Science, NARO(Japan))

Keywords:Antioxidant activities, Bioactive compounds, Coarse kneading, Japanese green tea, Tea processing

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. Coarse kneading (CK) is the first step of processing to destroy the structure of tea leaf at a certain temperature. Previous studies have shown that coarse kneading have the greatest impact on green tea quality during tea processing. However, few studies to date have provided information regarding the effects of coarse kneading on tea quality during the Japanese green tea manufacturing process. Thus, this study aimed to investigate the effects of processing conditions in coarse kneading step on bioactive compounds and antioxidant activities in tea infusion. The first flush fresh tea leaves were harvested at the experimental field of the national agriculture and food research organization (NARO) in Shizuoka, Japan in May 2019, and were processed continuously with different CK temperatures (34, 36 and 38 °C). The sample tea leaves were collected at each processing step and immediately cooled in a refrigerator. The processed tea leaves at each step were infused by hot distilled water at 95 °C for 5 min to examine bioactive compounds (total polyphenol content (TPC), total flavonoid content (TFC), and chlorogenic acid content (CA)) and antioxidant activities (1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid (ABTS) radical scavenging activity, ferric-reducing antioxidant power (FRAP) and metal ion chelating activity (MIC)). The results showed that bioactive compounds (TPC, TFC and CA) of tea infusion increased with increasing CK temperature. The values of the antioxidant activities of the tea infusion also showed a positive correlation to CK temperatures. ABTS and MIC trend of tea infusions showed the same trend as bioactive compounds as well as they were the highest at 38 °C CK. However, DPPH and FRAP values of tea infusions produced from 36 and 38 °C CK did not follow the same trend demonstrating higher of those value of 36 °C than those of 38 °C. In general, antioxidant activities trend of 38 °C tea infusion was more stable than those of 34 and 36 °C during the tea manufacturing process. These results indicate that coarse kneading temperature during green tea processing have a positive effect on the increase in the bioactive compounds of tea infusion and the stability of the antioxidant activities.