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Mass Transfer during Pressurized Low-Polarity Water Extraction of Phenolics and Carbohydrates from Flax Shives

2007; American Chemical Society; Volume: 46; Issue: 22 Linguagem: Inglês

10.1021/ie070351n

1520-5045

Jinwoo Kim, Giuseppe Mazza,

Microencapsulation and Drying Processes

The effects of pH-buffered water and NaOH solution on pressurized low-polarity water (PLPW) extraction were investigated to determine the optimal conditions for the extraction of lignocellulosic components from flax shives. A high NaOH concentration (0.1 M) and a high pH of buffered water (pH 13) increased the rates of extraction by increasing values of the effective diffusion coefficient (De) from 9.1 × 10-11 m2/s to 1.5 × 10-10 m2/s during PLPW extraction of free phenolic compounds. The concentration of NaOH exerted a significant effect on extraction of free phenolic compounds, whereas PLPW extraction of total carbohydrates was not significantly affected by variation of the pH and NaOH concentration. The maximum concentrations of free phenolic compounds (5.7 g/kg of dry flax shive (DFS)) and total carbohydrates (260 g/kg of DFS) were obtained using 0.1 M NaOH solution and water, respectively, at 230 °C and a flow rate of 2 mL/min. To determine the mechanism that controlled the PLPW extraction of free phenolic compounds and total carbohydrates, the extraction kinetics were studied using a two-site kinetic model and a thermodynamic model. The curves generated using these two models showed good fits to the experimental data within the tested range of flow rate, demonstrating that the extraction mechanism is controlled by both internal diffusion and external elusion. The kinetic values, including the fraction of the analyte released (F) and the kinetic constants obtained from the two-site kinetic model (k1 and k2), increased as the flow rate increased, indicating that the internal diffusion step is not totally independent of the flow rate, because the internal diffusion can be increased by the higher external concentration gradient that is caused by the higher flow rate.