Effect of storage humidity on quality of green tea
After storing green tea leaves at three different relative humidities (RH) (23, 69 and 81%) for 0, 3, 7, 14, 21 and 28 days, green teas were prepared by soaking 1g of the each leave sample in 100 mL of 70°C distilled water for 5min. Radical scavenging activity (RSA) , nitrite scavenging ability (NSA) , total phenolic contents (TPC) , catechins, and caffeine concentrations of the green teas were determined. RSA of the green teas increased with increasing storage period at RH of 23 and 69%. For example, RSA after 28 days storage at 23 and 69% RH were of 71.67 and 73.22%, while those of fresh samples were 68.84 and 67.26%, respectively. However, RSA of the green tea at 81% RH was the highest after 14 days of storage (76.79%). NSA of all the green teas increased with increasing storage period. NSA after 28 days storage at 23, 69, and 81% RH at pH 4.2 increased from 17.33, 18.65, and 17.93% (day 0) to 59.08, 53.43, and 52.96%, respectively. TPC of all the green teas were highest after 3 days of storage. TPC after 3 days storage at 23, 69, and 81% RH were 149.38, 132.02, and 136.12mg/mL, while those from fresh leaves were 106.28, 118.76, and 117.29mg/mL, respectively. Catechin and caffeine contents in green teas were also significantly affected by storage RH. For example, epigallocatechin gallate (EGCG) of green tea stored at 81% for 28 days increased from 0.87mg/mL to 5.54mg/mL compared to 0 day storage, and caffeine contents in the same conditions increased from 4.10mg/mL to 6.10mg/mL. The results indicated that the quality of green tea was significantly affected by storage humidity of green tea leaves.
Acknowledgements: This study was supported by Technology Development Program for Agriculture and Forestry, Ministry of Agriculture and Forestry, Republic of Korea. J.M. Lee was also supported by Brain Korea 21 Program.
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