This paper studies the correlation between fractal dimension of matrix microstructure of plant materials and extraction behavior using Astragalus root slices as examples. This work compared the yield of extracts on the conventional solvent soaking extraction of samples irradiated 3min by microwave 600W and 900W, respectively. Regarding to microwave treated samples, the area fractal dimensions (DL) of aperture in shape were estimated by using the slit island method on the basis of SEM images analysis, the volume fractal dimensions (DV) of pore size distribution inside matrix were also determined by the mercury injection method on the basis of measured results (6nm–40×105nm) by automatic mercury injection apparatus. Our findings are that, 900W treated sample behaves higher yield of extracts than 600W. The values of DL and DV both increase with increasing of microwave power. The higher values of DL correspond to the much irregular and deformed shape of aperture, which seems un-benefit for the extraction of component inside matrix. However, the higher values of DV correspond to the less concentration of pore size distribution, implying better connectivity of pore or channel at multi-scale (including trachea 20μm–50μm, aperture 0.1μm–1μm and plasmodesma 1nm–10nm in size) and permeability inside matrix during extraction, higher yield of extracts. It demonstrates that combining the two fractal dimensions can present much more information for better understanding of mass transfer behavior and the knowledge of material properties.

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