Impact of heating on chemical compositions of green tea liquor

Heating pasteurization changed flavour of green tea liquor and it was a technical barrier in ready-to-drink tea production. The effect of heating on chemical compositions of green tea liquor was investigated by high performance liquid chromatography and gas chromatography–mass spectrometry. With increase of heating temperature from 85 °C to 120 °C, the green tea liquor became darker and less green, but deeper yellow in colour. During the heating, epigallocatechin gallate, epigallocatechin, epicatechin and epicatechin gallate partially epimerized, and concentration of total catechins decreased. Twenty volatiles were identified and concentrations of pentanol, cis-3-hexenol, linalool oxide I, linalool oxide II and β-ionone were decreased while phenylacetaldehyde, linalool, linalool oxide III, α-terpineol and indole increased. The decline of volatiles with pleasant odours and increase of some volatiles with unpleasant odours, such as indole (animal-like) and α-terpineol (faint ammoniacal), was considered to be responsible for the change in flavour of green tea liquor. Treatment at 85 °C caused fewer changes in liquor colour and concentrations of catechins and volatiles and it is recommended that extraction and pasteurization of canned ready-to-drink green tea should be carried out at 85 °C or less.