Extraction of isoflavones from Puerariae lobata using subcritical water

As an alternative to organic solvents, subcritical water was employed for the first time as an effective solvent for the extraction of isoflavones from Puerariae lobata. Optimum experimental conditions for the extraction of the four main isoflavones were established by single factor experiments, and the optimum experimental conditions for total isoflavone extraction were established further by response surface methodology. With an extraction time of 45 min and a liquid/solid ratio of 1 : 20, the extraction yields of puerarin, 3′-methoxypuerarin, and daidzin reached maxima at extraction temperatures of 120 °C, 140 °C and 200 °C, respectively. Moreover, puerarin, 3′-methoxypuerarin and daidzin were degraded and produced various byproducts due to hydrothermal reactions at higher temperatures. The maximum extraction yields of the total isoflavones were obtained by response surface methodology (extraction time of 45 min, solid/liquid ratio of 1 : 15 and extraction temperature of 120 °C). Compared to conventional solvents, subcritical water utilized less solvent and required a shorter extraction time.