(188h) Optimization of Hot Pressurized Solvent Extraction Systems for the Recovery of Bio-Active Solutes
The use of hot pressurized solvents above their boiling point is well documented in the literature and applied for processing of agricultural and food substrates, conversion of biorenewable fuels, and material science. Studies in our research group have focused on the extraction of bio-active solutes from such substrates as grape marc, fruit berries, and tree bark; the primary target solutes being flavonoids exhibiting antioxidant properties. Pressurized hot solvent extraction above the boiling point of the solvent results in very rapid solute fluxes from the substrate due to enhanced solubility and accelerated mass transfer rates. To optimize the extraction process both modeling and experimental measurements have been made on flavonoid recoveries from grape marc using a Hansen three dimensional solubility parameter approach or semi-empirical equations for solute solubility in subcritical water. These approaches allow prediction of both the solute miscibility with the pressurized fluid as well as a semi-quantitative estimate of the magnitude of solubility enhancement as a function of temperature.
Studies have been performed using batch, semi-continuous batch, as well as accelerated solvent extraction (ASE) methods to study the recovery of anthocyanins from freeze-dried grape marc. These have included the environmentally-benign agents: supercritical carbon dioxide, subcritical water, and ethanol as a cosolvent. ASE experiments have been run using an increasing ethanol concentration at temperatures between 100- 140C by increasing the ethanol from 10-90 vol. %. Typically, as little as 10 vol. % ethanol, can recovery anthocyanins at approximately the 500 ìg/ 100 g dry weight level, thereby minimizing ethanol use for anthocyanin recovery. Separate ASE experiments have shown that acidified ethanol (pH = 2.3) can recover the target anthocyanins at a 95% level, while neat ethanol and water yield recoveries of 87 and 86%, respectively. Mineral acid - acidified water yielded only 45% anthocyanin recovery.
In an attempt to replace the mineral acid ? based acidification for aqueous extractions, our group have conducted batch extractions using high pressure SC-CO2 acidification of water - which will acidify water to a pH under 3.0. Using SC-CO2 pressures up to 60 MPa we have achieved 52% recovery of the anthocyanins without resorting to mineral acid addition using acidified methanol as a baseline (total anthocyanin) extraction solvent. Since higher anthocyanin yields result from the addition of ethanol aside from its prophylactic effect on retarding degradation of the target solutes (1st order extraction kinetics), a combination of a low percentage ethanol combined with CO2-acidified water may be an optimal solvent medium for the extraction of this flavonoid class from grape marc using very short extraction times (1 minute) at 120C.