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Keywords:

  • microstructure;
  • porosity;
  • tortuosity;
  • pore network;
  • oil distribution

Abstract

Microstructural properties play a key role to affect oil uptake and product quality during frying of foods. The objective of this study was to observe the complex microstructural changes and mass transfer mechanisms in potato disks during frying. The potato disks of 1.65 mm thickness were fried at 190 °C for 0, 20, 40, 60, and 80 s. X-ray micro-computed tomography (CT) was used for 3-dimensional (3D) imaging of microstructure of porous potato disks. Total porosity, pore size distribution, oil content, and air content of potato disks were calculated from resulting 3D data sets. Oil and air content measured by analysis of micro-CT images followed trends similar to Soxtec and gas pycnometry methods, respectively. Image analysis showed a significant change in pore size distribution as a function of frying time. Frying time was also observed to have an effect on tortuosity, which is an important microstructural fluid transport property. Tortuosity was measured by path length ratio method from 3D data sets obtained from image analysis. A linear inverse relationship was observed between porosity and tortuosity where tortuosity decreased with the increase of porosity. It was also observed that during frying, oil content increased with the decrease of tortuosity. This phenomenon indicated that the lower tortuosity created a less complicated and sinuous path, thus resulting in less resistance to oil penetration. Micro-CT technique can serve as an effective tool for elucidating microstructure of fried foods, and can provide complementary information to conventional lab techniques.

Practical Applications

Image analysis of micro-CT Images provided detailed microstructural information about fried potatoes. The 3D rendering of these images yielded information on porosity, pore size distribution, tortuosity, and spatial location of oil droplets. This helps to understand the frying mechanisms and improve the quality of fried foods.