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F. Pedreschi¹, J. M. AGUILERA¹, and C. A. Brown². (1) Department of Chemical Engineering and Bioprocesses, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860. P.O. Box 306, Santiago de Chile, 6904411, Chile, (2) Surface Metrology Laboratory, Worcester Polytechnic Institute, Mechanical Engineering Department, 100 Institute Rd., Worcester, MA 01609-2280

Surface topography is an important physical property of foods that influences not only their visual and sensorial aspects but also their behavior during processing. There is interest in characterizing different food topographies quantitatively. Food surfaces were measured with a scanning laser microscope (SLM) with spatial and vertical resolutions of 0.025mm. Scale-sensitive fractal analyses were applied to the measured surfaces using Surfrax (www.surfract.com), which employs linear and areal tiling to determine length-scale and area-scale relations. Conventional statistical analyses were also used to analyze the measured surfaces. Area-scale and length-scale fractal complexities (Lsfc and Asfc) and the smooth-rough crossover (SRC) were derived from the scale-sensitive fractal analyses (ASME B46 Fractal Document link at www.wpi.edu/~tral/). Both kinds of scale-sensitive fractal characterization parameters proved adequate to quantify and differentiate food surfaces (e.g., chocolate: Asfc=45.8; SRC=0.04 mm²; and a slice of bread: Asfc=271.9; SRC=0.48 mm²), which were smooth or porous to the naked eye. Surfaces of fried potato products (e.g., potato chips and French fries) had similar values of Asfc (222.6 and 249.0, respectively) and SRC (0.24 and 0.25 mm², respectively), and larger (implying more complex and rougher surfaces) than those of the raw potato (Asfc=172.97; SRC=0.040 mm²). Variability of surface texture characterization parameters as a function of the size of the measured region was used in selecting the size of regions for further analysis. The length-scale method of profile analysis (also called the Richardson or compass method) was useful in determining the directionality of the anisotropic textures of food surfaces. These measurement and analysis methods allow quantification of the surface textures of a wide range of foods at scales relevant to certain surface phenomena.