Effects of temperature and pressure on hydrothermal extraction kinetics of green coffee beans

Abstract

Hydrothermal extraction of green coffee beans was examined by using a semi-batch type apparatus and an optical cell for extracting beneficial compounds. Extraction curves were evaluated across varying temperatures (373–523 K) and pressures (0.6–2.1 MPa). At 473 K, increasing pressure enhanced the extraction of caffeoylquinic acids (CQAs), total phenolic content (TPC), antioxidant capacity (AOC), and caffeine. At 2.1 MPa, TPC remained constant with temperature, while AOC, CQAs, and caffeine initially increased then decreased at higher temperatures. Direct observations confirmed high temperature promoted extraction. An extraction model was proposed to account for decomposition of components at high temperatures, effectively reproducing experimental curves. This model estimated equilibrium values and rate constants representing initial extraction rate. The obtained results indicate that adjusting temperature, extraction time, and pressure can control extract composition during hydrothermal extraction of green coffee beans.