Influence of supercritical carbon dioxide extraction process temperature and co-solvent addition on the quality of green tea leaves extracts

Abstract

Interest in the separation of green tea extracts continues to grow due to its significant bioactivity, wide applicability as well as a large number of green tea spices, variety of extraction techniques, and lack of systematic data. The present early stage work was intended to estimate the effect of temperature and co-solvent addition on an amount of separated constituents from green tea (gunpowder tea variety, China) during the supercritical carbon dioxide (sc-CO2) extraction process. For this purpose, the temperature of the supercritical extraction process was increased up to 90 °C at a constant pressure of 30 MPa. After the selection of appropriate conditions, co-solvents (ethanol, ethanol/water, and water) were added to sc-CO2. Obtained extracts were analyzed regarding total phenolic content (TPC), total flavonoid content (TFC), DPPH radical scavenging activity, total chlorophyll, and total carotenoid content. The results of the supercritical extraction process were compared with the conventional extraction process (extraction using Soxhlet apparatus). The results showed that a linear decrease in the density of neat sc-CO2 led to a linear increase in extraction yields up to 5.5%. The addition of co-solvents had a variable effect on the amount of separated extracts. While it increased extraction yields at a lower temperature, it decreased extraction yields at a higher temperature. An increase in temperature for the extraction process with neat sc- CO2 also decreased TPC, TFC, chlorophylls, and carotenoids content. The addition of co-solvents to sc-CO2 increased amounts of tested compounds in obtained extracts. It was interesting to notice a decrease in the amount of tested compounds with an increase in water content during extractions. The highest values of TPC and TFC detected were 136.5 mg GAE/g and 40.7 mg QE/g, respectively. Extract solutions with a concentration of 20 mg/mL inhibited up to 65% of DPPH radical. Chlorophyll A, chlorophyll B, and carotenoids were detected in amounts up to 8.1 g/kg, 0.7 g/kg, and 0.5 g/kg of dry extract, respectively. Extracts obtained by conventional extraction contained higher amounts of TPC and TFC. On the other hand, those extracts contained lower amounts of total chlorophylls and carotenoids. Although supercritical extraction processes from green tea leaves have been performed for decades and its industrial application is present, there are still many unknowns. To the best of our knowledge, this is the first report in available literature on chlorophyll and carotenoid contents in supercritical extracts from green tea. Also tested process parameters enabled the achievement of higher yields (for neat sc-CO2) as well as higher TPC compared with previously reported ones for green tea supercritical extracts. Chemical analysis of obtained extracts is pending.