Fig. 1. Schematic diagram of supercritical CO₂ extraction system: 1, CO₂ cylinder; 2, electronic balance; 3, chiller; 4, CO₂ pump; 5, controller; 6, heating bath; 7, circulation pump; 8, extraction vessel; 9, separator 1; 10, separator 2; V-1, valve 1; V-2, valve 2; BPR, back pressure regulator; dotted lines, water; solid lines, CO₂.

Fig. 2. Effects of extraction temperature on the extraction yields of green tea components in dry green tea (wt.% of their initial contents) extracted with supercritical CO₂ at 300 bar and at a CO₂ flow rate of 8.5 g/min for 120 min. The particle size of the green tea was 425–710 μm, and ethanol (95%, v/v) was utilized as a cosolvent at a concentration of 4.6 g per 100 g of CO₂. Control indicates the green tea before extraction.

Fig. 3. Effects of extraction pressure on the extraction yields of green tea components in dry green tea (wt.% of their initial contents) extracted with supercritical CO₂ at 70 °C and at a CO₂ flow rate of 8.5 g/min for 120 min. The particle size of the green tea was 425–710 μm, and ethanol (95%, v/v) was used as a cosolvent at a concentration of 4.6 g per 100 g of CO₂. Control indicates the green tea before extraction.

Effect of drying on the composition analysis of green tea

Each value is expressed as mean ± standard deviation from triplicate data.

Supercritical CO₂ extraction yields of caffeine and catechins from green tea leaves with particle sizes of 425–710 μm when operated at a CO₂ flow rate of 8.5 g/min, a pressure of 300 bar, and a temperature of 70 °C for 120 min with cosolvents

Each green tea sample was extracted in triplicate, each extract was analyzed by HPLC in duplicate, and the calculated extraction yields were expressed as means ± standard deviations.