Browsing by Author "Pedreschi, F"

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    Characterization of food surfaces using scale-sensitive fractal analysis
    (FOOD NUTRITION PRESS INC, 2000) Pedreschi, F; Aguilera, JM; Brown, CA
    Length-scale and area-scale analyses, two of the scale-sensitive fractal analyses performed by the software Surfrax www.surfract.com, were used to study food surfaces measured with a scanning laser microscope (SLM). The SLM measures surfaces, or textures (i.e., acquires topographical data as a collection of heights as a function of position), at a spatial and vertical resolution of 25 mu m. The measured textures are analyzed by using linear and areal tiling (length-scale and area-scale analysis) and by conventional statistical analyses. Area-scale and length-scale fractal complexities (Lsfc and Asfc) and the smooth-rough crossover (SRC) are derived from the scale-sensitive fractal analyses. Both measures proved adequate to quantify and differentiate surfaces of foods (e.g., chocolate and a slice of bread), which were smooth or porous to the naked eye. Surfaces generated after frying of potato products (e.g., potato chips and French fries) had similar values of Asfc and SRC, and larger (implying more complex and rougher surfaces) than those of the raw potato. Variability of surface texture characterization parameters as a function of the size of the measured region was used in selecting the size of the measured regions for further analysis. The length-scale method of profile analysis (also called the Richardson or compass method) was useful in determining the directionality or lay of the anisotropic texture on food surfaces.
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    Characterization of the surface properties of chocolate using scale-sensitive fractal analysis
    (TAYLOR & FRANCIS INC, 2002) Pedreschi, F; Aguilera, JM; Brown, CA
    A scanning laser microscope was used at its highest resolution (25 mum) to study the surface of three kinds of commercial chocolate. Data of measured surfaces were analyzed by scale-sensitive fractal analysis (SSFA) using linear and area tiling (length-scale and area-scale analysis) and by conventional statistical analyses for roughness. Area-scale and length-scale fractal complexities (Lsfc and Asfc) and the smooth-rough crossover (SRC) derived from SSFA proved adequate to characterize the surface roughness of chocolate and changes in topography as a result of bloom. The three chocolate surfaces analyzed had similar values of Asfc, Lsfc and ARa. Nestle milk chocolate presented significant higher values of SRC than those corresponding to the other two kinds of chocolate analyzed (e.g., 0.051 mm(2) vs. 0.038 and 0.037 mm(2) in the case of area-scale sensitive analysis) implying a rougher surface.
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    Classification of potato chips using pattern recognition
    (WILEY, 2004) Pedreschi, F; Mery, D; Mendoza, F; Aguilera, JM
    An approach to classify potato chips using pattern recognition from color digital images consists of 5 steps: (1) image acquisition, (2) preprocessing, (3) segmentation, (4) feature extraction, and (5) classification. Ten chips prepared for each of the following 6 conditions were examined: 2 pretreatments (blanched and unblanched) at 3 temperatures (120 degreesC, 150 degreesC, and 180 degreesC). More than 1500 features were extracted from each of the 60 images. Finally, 11 features were selected according to their classification attributes. Seven different classification cases (for example, classification of the 6 classes or distinction between blanched and unblanched samples) were analyzed using the selected features. Although samples were highly heterogeneous, using a simple classifier and a small number of features, it was possible to obtain a good performance value in all cases: classification of the 6 classes was in the confidence interval between 78% and 89% with a probability of 95%.
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    Segmentation of colour food images using a robust algorithm
    (ELSEVIER SCI LTD, 2005) Mery, D; Pedreschi, F
    In this paper, a robust algorithm to segmenting food image from a background is presented using colour images. The proposed method has three steps: (i) computation of a high contrast grey value image from an optimal linear combination of the RGB colour components; (ii) estimation of a global threshold using a statistical approach; and (iii) morphological operation in order to fill the possible holes presented in the segmented binary image. Although the suggested threshold separates the food image from the background very well, the user can modify it in order to achieve better results. The algorithm was implemented in Matlab and tested on 45 images taken in very different conditions. The segmentation performance was assessed by computing the area A(z) under the receiver operation characteristic (ROC) curve. The achieved performance was A(z) = 0.9982. (C) 2004 Elsevier Ltd. All rights reserved.
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    Some changes in potato chips during frying observed by confocal laser scanning microscopy (CLSM)
    (SAGE PUBLICATIONS LTD, 2002) Pedreschi, F; Aguilera, JM
    Confocal laser scanning microscopy (CLSM) was used in fluorescence mode for oil and cell wall detection, and in reflective mode to observe the surface morphology of potato chips. Oil distribution in chips fried at 170degreesC in oil mixed with the thermoresistant probe Nile Red was studied as the crust developed during frying. Oil was trapped only in intercellular spaces for short frying times while at longer times it was strongly linked to the developed crust microstructure (not only in intercellular spaces but also over some cells) and not easily extractable by hexane washing. Chips infiltrated with a solution of the dye Congo Red (CR) before frying revealed drastic changes in cell walls but no signs of rupture during frying at the magnification used in this research (20X). Topographical data acquired by CLSM in reflective mode confirmed that several cells are broken during the cutting operation. Image representation of the reconstructed surface of a fried chip (170 degreesC, 3 min) allowed observe oil location in potato surface after frying.
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    Textural characterization and kinetics of potato strips during frying
    (WILEY, 2001) Pedreschi, F; Aguilera, JM; Pyle, L
    A single puncture test (SPT) system was designed to determine textural changes in potato strips in situ during frying at 160, 175, and 190 degreesC. Puncture force changed drastically with time and depth in the strip during frying. Force-distance curves were expressed as representative textural parameters as CF (core force), RF (rupture force), and S (springiness). Normalized parameters CF* and S* for core force and springiness were used In modeling textural changes in the core during initial tissue softening and later crust development process, respectively. High frying temperatures accelerated the process, and the finished fried potato strip was a composite structure made of a hard crust and a soft core.