DSpace Angular :: Browsing by Author "Aguilera, JM"

Browsing by Author "Aguilera, JM"

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Application of image analysis for classification of ripening bananas
(WILEY, 2004) Mendoza, F; Aguilera, JM
A computer vision system was implemented to identify the ripening stages of bananas based on color, development of brown spots, and image texture information. Nine simple features of appearance (L* a*, b* values; brown area percentage, number of brown spots per cm(2); and homogeneity, contrast, correlation: and entropy of image texture) extracted from images of bananas were used for classification purposes. Results show that in spite of variations in data for color and appearance, a simple classification technique is as good to identify the ripening stages of bananas as professional visual perception. Using L* a*, b* bands, brown area percentage, and contrast,it was possible to classify 49 banana samples in their 7 ripening stages with an accuracy of 98%. Computer vision shows promise for online prediction of ripening stages of bananas.
Applications of microprobe Raman spectroscopy in food science
(SAGE PUBLICATIONS LTD, 2002) Celedon, A; Aguilera, JM
The Raman microprobe combines the analytical properties of Raman spectroscopy and the visualization capabilities of a high quality microscope, allowing localization and identification of species and phases in time intervals of seconds to a few minutes with a spatial resolution down to 1 mum. This article describes the basic principles of operation of the Raman microprobe and some applications that are important in food technology: in situ differentiation between sucrose and lactose crystals and of amorphous and crystalline phases in sucrose; detection of semi-crystalline and gelatinized zones in starch granules, and phase transitions in cocoa butter after heating (melting)/cooling (crystallization) cycles. Extensions of these applications cover the entire range of food constituents.
Assessment of the quality of heated oils by differential scanning calorimetry
(AMER CHEMICAL SOC, 1998) Gloria, H; Aguilera, JM
Differential scanning calorimetry (DSC) was used to follow changes in the thermal characteristics of commercial frying oils (sunflower seed, colza, and groundnut) during heating at 180 degrees C for up to 10 h. DSC tracings of oils scanned from 10 to -80 degrees C were characterized by a single crystallization peak (CP) at -43 to -48 degrees C. Heating of oils resulted in a progressive shift of the CP to lower temperatures and reduced enthalpies of crystallization (EC). The temperature of the CP decreased as much as 27 degrees C, and the EC was reduced by almost 90% after heating for 10 h. These changes in thermal characteristics correlated well with the appearance of polar compounds, the increase in viscosity, and color changes of the oil. DSC is a fast method of analysis, requires small samples (15-60 mg) with minimal preparation, and may be implemented directly in fried products.
Characterization of food surface roughness using the glistening points method
(ELSEVIER SCI LTD, 2004) Quevedo, R; Aguilera, JM
Several properties of foods, most notably visual perception and color, depend on the complexity of their outer surface. The so-called glistening point method based on specular reflection of an incident light beam is a simple, non-invasive optical technique used to quantify the roughness of a surface. Assuming that a surface has a macroscopic random Gaussian roughness distribution, the method determines two parameters: the correlation length (L) and the rms amplitude (sigma). Rougher surfaces have higher L and sigma values. Results show that the glistening point method is suitable for analysing food surfaces at the microscopic scale and is also useful to quantitatively follow changes in food surface roughness as during chocolate blooming or after removal of the outer wax layer in fruits. (C) 2003 Elsevier Ltd. All rights reserved.
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.
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.
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%.
Description of food surfaces and microstructural changes using fractal image texture analysis
(ELSEVIER SCI LTD, 2002) Quevedo, R; Carlos, LG; Aguilera, JM; Cadoche, L
Images, particularly photomicrographs, provide qualitative information about surfaces of foods and cells. Methods to analyze the texture of images such as fractional Brownian motion (FBMM), box counting (BCM), and fractal dimension (FD) estimation from frequency domain (FDM), were used to numerically describe the surfaces of foods and the microstructure of potato cells. A FD was calculated for each image using the power-law scaling for self-similar fractals. The surface of analyzed foods had FD varying from 2.22 for chocolate to 2.44 for pumpkin shell. As reference, the FD of sandpaper having increasing grain size or roughness varied from 2.37 to 2.65. FD was also useful to numerically describe microstructural changes with time of an isolated potato cell during heating in oil and of the surface of chocolate undergoing crystallization of fats (blooming). (C) 2002 Elsevier Science Ltd. All rights reserved.
Determination of kinetics of gelation of whey protein and cassava starch by oscillatory rheometry
(ELSEVIER SCIENCE BV, 1997) Aguilera, JM; Rojas, GV
Kinetics of heat-induced gelation of cassava starch (CS) suspensions, whey protein isolate (WPI) solutions and mixed blends at 10% total solids (TS) were followed by small deformation oscillatory shear rheometry in the temperature range 70-90 degrees C. Storage moduli (G') of WPI solutions (4-14% TS) increased steadily following simple first order kinetics. G' of CS suspensions (8-14% TS) increased rapidly to a peak and decayed steadily later. A model consisting of a two-step reaction with a reversible step was proposed for gelation of CS. G' of WPI gels were two orders of magnitude higher than those of CS. Mixed gels having a starch fraction = 0.2 had G' similar to those of pure WPI gels. (C) 1998 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd.
Determination of oil in fried potato products by differential scanning calorimetry
(AMER CHEMICAL SOC, 1997) Aguilera, JM; Gloria, H
Differential scanning calorimetry (DSC) was used to determine the oil uptake of commercial frozen par-fried potatoes after frying at 180 degrees C in colza/soybean oil. The enthalpy and temperature range of the crystallization peak for the pure frying oil were 47.2 J/g and -44 to -50 degrees C, respectively. DSC was performed by cooling samples of crust and core of fried potatoes from 10 to -60 degrees C at 1 degrees C/min and the oil content calculated from the peak area. The crust contained almost 6 times as much oil as the central core (23.6% vs 4%, dry weight basis), as visualized by light microscopy. Only 87% of the oil in the intact crust can be removed by solvent extraction, the rest being extractable only after grinding. Deviation between DSC and Soxtec extraction methods was less than 3%. The DSC method is fast, specific, and reliable, does not use solvents, requires smaller samples (<100 mg) than conventional solvent extraction methods, and can also detect freezable water.
Effect of kappa-carrageenan on the gelation of horse mackerel (T-murphyi) raw paste surimi-type
(SAGE PUBLICATIONS LTD, 2004) Ortiz, J; Aguilera, JM
Gelation of fresh (unfrozen) raw surimi-type paste (RS paste) from horse mackerel (T murphyi) was studied in the presence Of kappa-carrageenan (0.5, 1, 2% Ckappa) and KCl (0.5-2%) as a substitute for NaCl. Gelation was traced by measuring the storage modulus (G') during heating-cooling cycles. Variations in G' during the heating stage of the mixed system RS-Ckappa characterised the presence of a phase separation in this stage due to Ckappa solubilitation (at about 50degreesC) as well as to RS gelation (35-80degreesC) in the mixture. It was also observed that when Ckappa was added as a single ingredient. it inhibited RS gelation as a function of its concentration (>2%). Nevertheless, during the cooling stage, the final G' value for the RS-2% Ckappa mixed system was greatly increased. This reinforcing would be caused by further (cold) Ckappa gelation in the mixture. It is theorised that Ckappa might act by forming 'packed' microgels within the RS protein gel network, which is favoured upon application of a moderate (40degreesC, 60 min) thermal treatment rather than when an extreme (90degreesC, 20 min) treatment is applied. On the other hand, although KCl enhanced gelation of the 2% Ckappa solution, addition of this salt to the RS-2% Ckappa mixture did not improve its gelation. Rheological information was complemented with observation of the resulting structures by scanning electronic microscopy (SEM).
Glass transition temperature (T-g) and water activity (a(w)) of dehydrated apple products
(WILEY-BLACKWELL, 1999) Welti Chanes, J; Guerrero, JA; Barcenas, ME; Aguilera, JM; Vergara, F; Barbosa Canovas, GV
The onset glass transition temperature (T-go) of Granny Smith apple products was evaluated as a function of drying conditions (air drying and freeze-drying) and moisture and water activity (a(w)) levels. T-go was determined in the 0-0.75 a(w) range, and it was found to have a maximum value at a(w) = 0 (T-go = 4.5 +/- 1.6C) for freeze-dried apple and a minimum value at a(w) = 0.75 (T-go = -81.4 rt 0.1C) for freeze-dried apple juice. A linear relationship between T-go and a(w) was obtained in all cases. Theoretical T-go values at a(w) = 0 were calculated using these equations, and were within the range of 3.0C (freeze-dried apple) and 10.5C (apple dehydrated at 30C). When Gordon and Taylor's linear model was applied to the experimental data of all the apple products, K values within the range 2.4 (freeze-dried apple juice) and 3.6 (apple dehydrated at 60C), and the theoretical T-g of solids values at a(w) = 0 between the range -16.3C (freeze-dried apple juice) and -1.9C (apple dehydrated at 60C) were obtained. No effect of the type of drying on the value of T-g was detected.
Glass transitions and shrinkage during drying and storage of osmosed apple pieces
(ELSEVIER SCIENCE BV, 1998) del Valle, JM; Cuadros, TRM; Aguilera, JM
The relationship between shrinkage during drying and 'glass'-'rubber' transitions of apple tissue was studied. Our results did not indicate that structural collapse of apple pieces can be reduced by diminishing the difference Delta T between drying temperature and glass transition temperature (T-g) of the fruit matrix. Apple shrinkage was not consistently depressed by reducing drying temperature, infusing larger amounts of T-g-depressing agents (sucrose, maltose, lactose) or infusing similar amounts of solutes with higher anhydrous T(g)s. However, sugars added during osmotic dehydration pretreatments help decreasing structural collapse during subsequent air drying, which was reflected by a 20-65% increase in final volume of samples treated with 50% sucrose and maltose solutions as compared to an air-dried, control sample. Dried samples remained in the "rubbery" state after drying and shrunk during subsequent storage. (C) 1999 Published by Elsevier Science Ltd on behalf of the Canadian Institute of Food Science and Technology. All rights reserved.
Limpness of fried potato slabs during post-frying period
(WILEY, 2005) Miranda, ML; Aguilera, JM; Beriestain, CI
The rupture stress (RS) of fried potato slices (1.60 mm thick) and of the crust of fried potato slabs (FPS) having lengths of 60 mm and sides of 8, 10 and 12 mm, was determined during the post-frying period by a puncture test. The RS of fried potato slices decreased as water activity increased from 0.22 to 0.85. The RS of FPS diminished in the first 5-6 min when exposed to ambient conditions and remained almost constant thereafter A novel videotape technique and image analysis were used to follow deflection of FPS in the post-frying period. An apparent modulus based on the composite structure of FPS and calculated from beam mechanics decreased with time in a trend similar to that of the textural parameters. We concluded that changes in physical properties of the crust because of moisture accumulation are the major causes of loss of texture (limpness) in FPS during the post-frying period.
Microstructural changes of potato cells and starch granules heated in oil
(ELSEVIER SCIENCE BV, 2001) Aguilera, JM; Cadoche, L; Lopez, C; Gutierrez, G
A method that mimics the frying operation was implemented to observe microstructural changes in potato cells and starch. Isolated cells were obtained by successive treatments of potato tissue with acid and alkali solutions. Potato cells were heated in oil at a rate of 40 degreesC/min or directly in hot oil (180 degreesC) using a hot stage attached to a light microscope and studied by video-microscopy. Starch granules in cells underwent rapid gelatinization, deformation and compaction into one mass that occupied the whole volume of the cell. After dehydration cells showed a distinctive outer zone and a homogeneous core. Cell walls showed no signs of disruption but at temperatures > 100 degreesC a reduction in cell area occurred. Immersion of cells in hot oil resulted in rapid swelling of starch. Relative projected area increased by 12% after 45 s of heating. Wet isolated starch granules began to expand and gelatinize at 65 degreesC and became disrupted at 120 degreesC. No changes were observed in dry starch granules subjected to a similar treatment. (C) 2001 Elsevier Science Ltd. All rights reserved.
Microstructure and food product engineering
(INST FOOD TECHNOLOGISTS, 2000) Aguilera, JM
Modeling the effect of microstructure on food extraction
(FOOD NUTRITION PRESS INC, 2001) Crossley, JI; Aguilera, JM
Several cases of extraction of food components were analyzed applying the diffusion theory and Fick's second law to different microstructural architectures. A mathematical algorithm was developed for a two-dimensional heterogeneous system and programmed in MATLAB. Architectures examined include: (1) structure with straight pores, (2) flake with impermeable platelets, (3) matrix with impermeable dispersed particles and, (4) cellular material. Results show that the architecture of phases in the solid matrix is more important than parameters normally used to correct the diffusivity for structural effects (tortuosity, porosity, volume fraction, etc.). Simulated extraction curves were similar to those obtained from experimental data where an empirical effective diffusivity was calculated. These results suggest a more fundamental approach to modeling of extraction in foodstuffs based on the microstructure and local architecture.
Note. Effect of thermal history on the gelation of horse mackerel (T-murphyi) raw paste surimi-type
(ASPEN PUBL INC, 2000) Aguilera, JM; Ortiz, J
Fresh paste from horse mackerel (T. murphyi) surimi-type, was processed during setting using (2%) KCl. The paste was subjected to different heating and cooling cycles. The salt produced an improvement in kamaboko-type gel formation. The heating and cooling cycles enhanced the setting process and improved textural quality of the resulting gel, mainly when the heating before cooling was slow. The setting process was characterized by several physical parameters: storage module (G'), using an oscillatory rheological technique, and apparent Young module (E), by means of mechanical compression tests. The enthalpic changes for gelification of the paste were determined using differential scanning calorimetry.
Oil absorption during frying of frozen parfried potatoes
(INST FOOD TECHNOLOGISTS, 2000) Aguilera, JM; Gloria Hernandez, H
A tracer method was used to assess the uptake of oil by commercial frozen parfried potatoes fried (180 degrees C, 150 s) in colza oil (CO) involving a short post-frying immersion in hot coconut fat (CF), CO and CF were determined directly in the crust by differential scanning calorimetry (crystallization temperature and enthalpy -42.7 degrees C/50 J/g and 10 degrees C/71 J/g, respectively). Oil uptake by the crust during frying in CO or CF was similar (average 25.3%). Potato samples transferred immediately after frying in CO to the CF bath had most of the CO absorbed replaced by CF after a 10 s post-frying, meaning that CO was readily accessible in the crust structure. Samples fried in CO and cooled for up to 60 s before transfer to hot CF showed only partial replacement of CO. Oil wetting the surface of the sample at the end of frying was estimated as 70 to 80% of the total oil uptake. Formation of the crust (frying time > 1 min) was required for oil to migrate into intercellular spaces that are dynamically formed during frying and thus accessible to CF and solvents.
Quantification of microstructural changes during first stage air drying of grape tissue
(ELSEVIER SCI LTD, 2004) Ramos, IN; Silva, CLM; Sereno, AM; Aguilera, JM
Microstructural changes in cells of Ruby grape (Vitis vinifera) quarters were monitored during first stage of convective air drying, under a stereo-microscope. A gradual overall shrinkage of grape cells was observed during the process. The cellular parameters: area, perimeter, major and minor axis length, Feret diameter, elongation, roundness and compactness, were quantified by image analysis. It was verified that cell dimensions suffered modifications during drying, but their shape remained unchanged. These microstructural changes showed a smooth exponential decrease with time, and a first-order kinetic model was satisfactorily fitted to the data. Temperature increased the rate of cellular shrinkage and this effect followed an Arrhenius type behaviour. Increasing temperature from 20 to 60 degreesC resulted in a 350% increase of the area change rate. For the parameters related to cellular dimensions, the magnitude of the values were 10(-3) min(-1) for the rate of change at 40 degreesC and 3 kJ/mol for the activation energy. (C) 2003 Elsevier Ltd. All rights reserved.

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