DSpace Angular :: Browsing by Author "Aguilera, Jose M."

Browsing by Author "Aguilera, Jose M."

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Biological indicators to estimate the prevalence of gray mold and hairline cracks on table grapes cv. Thompson Seedless after cold storage
(ELSEVIER SCIENCE BV, 2009) Pablo Zoffoli, Juan; Latorre, Bernardo A.; Rodriguez, Jessica; Aguilera, Jose M.
Gray mold caused by Botrytis cinerea and hairline cracks are the major cold storage deterioration problems of table grapes (Vitis vinifera). Currently. table grapes are treated with sulfur dioxide (SO2), but this treatment does not sufficiently and consistently control B. cinerea. This is probably associated with latent infections that are poorly controlled with SO2, and to the increased berry propensity to develop hairline cracks following SO2 treatment. Therefore, the objective of this work was to obtain an early biological indicator to segregate grape lots at harvest to later develop according to the potential gray mold and hairline cracks. In this study, it was possible to distinguish gray mold infections at the stylar end, cheek, and base of the berries. However, on commercial SO2-treated lots of 'Thompson Seedless' table grapes, the occurrence of gray mold after cold storage was best predicted (Y= 0.45X, R-2 = 0.84, P < 0.001) by the number of gray mold infections that developed at the base of the berry of surface-disinfected (100 mu L L-1 SO2 for 1 h) grapes that were incubated at harvest in humid chambers (100% relative humidity) for 2 d at 0 degrees C then 5 d at 20 degrees C. Similarly, the occurrence of hairline cracks after cold storage was best predicted (Y= 1.48 + 0.51X, R-2 = 0.66, P= 0.0002) by the number of hairline cracks induced at harvest by dipping berries in 0.1 mol L-1 citric acid, pH 2, for 3 h at 20 degrees C, and stained with 0.1 mol L-1 methylene blue for 30 s at 20 degrees C. At harvest, cuticle content and porosity also predicted the occurrence of hairline cracks after cold storage. However, the cuticle content at harvest did not significantly predict gray mold occurrence at the berry base after cold storage. The occurrence of gray mold in commercial SO2-treated lots after cold storage was predicted by the prevalence of gray mold at the berry base at harvest. Similarly, the occurrence of hairline cracks after cold storage was predicted by the ability to induce hairline cracks at harvest by acidic pH. Further refinement in this research is needed before using these biological indicators to segregate table grape lots commercially. (C) 2008 Elsevier B.V. All rights reserved.
Calibrated color measurements of agricultural foods using image analysis
(ELSEVIER, 2006) Mendoza, Fernando; Dejmek, Petr; Aguilera, Jose M.
A computer vision system (CVS) was implemented to quantify standard color of fruit and vegetables in sRGB, HSV and L*a*b* color spaces, and image capture conditions affecting the results were evaluated. These three color spaces are compared in terms of their suitability for color quantification in curved surfaces. The results show that sRGB standard (linear signals) was efficient to define the mapping between R'G'B' (no-linear signals) from the CCD camera and a device-independent system such as CIE XYZ. The CVS showed to be robust to changes in sample orientation, resolution, and zoom. However, the measured average color was shown to be significantly affected by the properties of the background and by the surface curvature and gloss. Thus all average color results should be interpreted with caution. L*a*b* system is suggested as the best color space for quantification in foods with curved surfaces. (C) 2006 Elsevier B.V. All rights reserved.
Colour and image texture analysis in classification of commercial potato chips
(ELSEVIER, 2007) Mendoza, Fernando; Dejmek, Petr; Aguilera, Jose M.
The images of commercial potato chips were evaluated for various colour and textural features to characterize and classify the appearance and to model the quality preferences of a group of consumers. Features derived from the image texture contained better information than colour features to discriminate both the quality categories of chips and consumers' preferences. Entropy of a* and V and energy of b* from imaees of the total chip surface, average and variance of H and correlation of V from the images of spots and/or defects (if they are present). and average of L* from clean images (chips free of spots and/or defects) showed the best correspondence with the four proposed appearance quality groups (A: 'pale chips', B: 'slightly dark chips, C: 'chips with brown spots', and D: 'chips with natural defects'), giving classification rates of 95.8% for training data and 90% for validation data when linear discriminant analysis (LDA) was used as a selection criterion. The inclusion of independent colour and textural features from images of brown spots and/or defects and their clean regions of chips improved the resolution of the classification model and in particular to predict 'chips with natural defects'. Consumers' preferences showed that in spite of the 'moderate' agreement among raters (Kappa-value = 0.51), textural features have potential to model consumer behaviour in the respect of visual preferences of potato chips. A stepwise logistic regression model was able to explain 86.2% of the preferences variability when classified into acceptable and non-acccptable chips. (c) 2007 Elsevier Ltd. All rights reserved.
Determination of a representative area element (RAE) based on nonparametric statistics in bread
(ELSEVIER SCI LTD, 2011) Ramirez, Cristian; Aguilera, Jose M.
The concept of representative area element (RAE) was applied to quantify the air cell present in pre-sliced bread. Ten slices from bread were selected and each divided into nine subareas where 60 air cells were measured. To determine the RAE, one to nine sampling areas were considered and five positions in the image were randomly selected and compared by nonparametric statistic and the fluctuation of mean air cell area method. The RAE was attained when the air cell area size distribution curves for each sampling area did not present significant differences. Hence, the RAE size was 67% of the image using the nonparametric method (equivalent to six subareas of the nine subareas that form the image), whereas the RAE could not be estimated using the fluctuation of mean air cell area method. Therefore, nonparametric statistics are a useful tool to determine the RAE in structures with size distributions that do not fit a normal distribution. (C) 2010 Elsevier Ltd. All rights reserved.
Effect of native crystalline structure of isolated potato starch on gelatinization behavior and consequently on glycemic response
(ELSEVIER, 2012) Parada, Javier; Aguilera, Jose M.
Effect of crystalline structure of two isolated potato starches on gelatinization and glycemic response was studied. Both starches showed to possess different fine structures. Starch 1 exhibited a typical B-type X-ray diffraction pattern, while Starch 2 exhibited an X-ray diffraction pattern suggesting the presence of imperfections of the general B-type crystalline structure (peak at 5.5 degrees 2 theta was absent), hence disarraying the structure order. This difference was reflected in the gelatinization behavior and consequently in the glycemic response. Starch 2 started to melt at lower temperature than Starch 1 (e.g. T-o was 60.9 and 61.84 degrees C, respectively, to native starches), and residual gelatinization enthalpy (Delta H) of Starch 2 was always smaller than that of Starch 1 when heated at 54-65 degrees C for 10 min. Glycemic response was increased as gelatinization degree (DG) increased in starches independent from the native crystalline structure (area under curve = 2.59 x DG-75.83, R-2=0.986; maximum concentration of postprandial blood glucose=0.042 x DG-0.23, R-2=0.935). Results suggested that native crystalline structure of isolated potato starch affects the glycemic response of heated starches by affecting the gelatinization behavior. (C) 2011 Elsevier Ltd. All rights reserved.
Effect of surface topography on color and gloss of chocolate samples
(ELSEVIER SCI LTD, 2006) Briones, Vilbett; Aguilera, Jose M.; Brown, Christopher
Different surface roughnesses of six chocolate samples were produced by molding over sandpaper of different graininess. Surfaces were examined for roughness (laser scanning microscopy), color and image texture (digital vision system) and gloss (glossmeter). Samples exhibited significantly different roughness among them expressed by the two parameters used to characterize their surfaces: the statistical average roughness, ARa (mu m), and the area-scale fractal complexity (dimensionless), Asfc. Surfaces of sandpaper and chocolate samples were highly correlated with these two parameters. Surface elements related to roughness were in the order of 3-14 mu m. Gloss of chocolate surfaces diminished exponentially as roughness increased while color (L*, lightness and whiteness index) decreased linearly. Parameters describing image texture, entropy and homogeneity, varied linearly with Asfc values. The structure of the surface of chocolate bars seems to play a decisive role in visual quality appearance. (c) 2005 Elsevier Ltd. All rights reserved.
Gloss measurements of raw agricultural products using image analysis
(ELSEVIER, 2010) Mendoza, Fernando; Dejmek, Petr; Aguilera, Jose M.
Gloss is considered one of the most important visual attributes of many foods, which is difficult to measure objectively. In this paper, a gloss imaging system (GIS) was implemented to evaluate the suitability of four indexes for measuring gloss from intensity images in flat and curved surfaces and to analyze gloss of some fruits and vegetables. Three indexes were computed from goniometric curves: maximum intensity (MI), width of the curve at 50% (WC), and area under the curve (AC). The fourth index was computed from the same intensity images as the average of the reflected luminance flux (LF) at the surface of the image. The results showed linear relationships (R-2 = 0.97) when values of MI, AC, LF for flat and curved gloss targets in the range of 4-90 units of gloss (GU) were compared with their standard gloss levels. However, the measured gloss was significantly affected by curvature and unevenness of the surface of fruits and vegetables. In spite of this, we concluded that a colour digital camera of moderate cost combined with simple image analysis procedure can yield parameters which correlate highly with the gloss appearance of fruits and vegetables and allow measurements over a very wide range of gloss with high sensitivity. (C) 2009 Elsevier Ltd. All rights reserved.
Identifying industrial food foam structures by 2D surface image analysis and pattern recognition
(ELSEVIER SCI LTD, 2012) Germain, Juan C.; Aguilera, Jose M.
Bubbles are fundamental structural elements in several food products modulating density, rheology, texture, appearance and mouthfeel. Foams and aerated structures are characterized by their gas content, stability, bubble size and distribution. However, these measures alone cannot fully describe the complexity of bubble-containing structures. We have used three image analysis methods (Euler characteristic, Minkowski fractal and image texture) to characterize foam structure, and canonical and Bayesian discriminant analysis to identify/classify different foam architectures. This work describes results of this methodology on liquid foams stabilized by proteins at varying concentration and pH levels. Results indicated that groups of three structural parameters (among the 57 calculated) could successfully identify foam structures with different characteristics but unfortunately no single set of features could be used ubiquitously. Additional foam structure information as determined in this work can help to better understand these systems and the impact of bubbles on the physical properties of aerated foods. (C) 2012 Elsevier Ltd. All rights reserved.
Image Analysis of Representative Food Structures: Application of the Bootstrap Method
(WILEY, 2009) Ramirez, Cristian; Germain, Juan C.; Aguilera, Jose M.
Images (for example, photomicrographs) are routinely used as qualitative evidence of the microstructure of foods. In quantitative image analysis it is important to estimate the area (or volume) to be sampled, the field of view, and the resolution. The bootstrap method is proposed to estimate the size of the sampling area as a function of the coefficient of variation (CVBn) and standard error (SEBn) of the bootstrap taking sub-areas of different sizes. The bootstrap method was applied to simulated and real structures (apple tissue). For simulated structures, 10 computer-generated images were constructed containing 225 black circles (elements) and different coefficient of variation (CVimage). For apple tissue, 8 images of apple tissue containing cellular cavities with different CVimage were analyzed. Results confirmed that for simulated and real structures, increasing the size of the sampling area decreased the CVBn and SEBn. Furthermore, there was a linear relationship between the CVimage and CVBn. For example, to obtain a CVBn = 0.10 in an image with CVimage = 0.60, a sampling area of 400 x 400 pixels (11% of whole image) was required, whereas if CVimage = 1.46, a sampling area of 1000 x 100 pixels (69% of whole image) became necessary. This suggests that a large-size dispersion of element sizes in an image requires increasingly larger sampling areas or a larger number of images.
In vitro Digestibility and Glycemic Response of Potato Starch is Related to Granule Size and Degree of Gelatinization
(WILEY, 2009) Parada, Javier; Aguilera, Jose M.
Starch granule microstructure affects the digestion of starch and its nutritional impact; however, the exact relationship between both factors is not clear. This study reports quantitative relationships between granule size (length and polygonal area), degree of gelatinization (DG), in vitro digestibility (by enzymatic methods), and glycemic response of potato starch granules gelatinized to various extents by heating at several constant temperatures in the range of 55 to 65 degrees C. DG measured by differential scanning calorimetry was closely related with heating temperature (R-2 = 0.997), size parameters of granules (measured by image analysis), in vitro digestion, and in vivo glycemic response (R-2 of adjusted models > 0.9); shape parameters of granules (measured by image analysis) were not related with DG. Results demonstrate that DG of starch strongly affects its digestibility in vitro, and may influence the postpandrial glycemic response. Future studies should be performed to investigate the effect of potato starch gelatinization on the nutritional impact at other temperatures and in more complex matrices.
Mechanical properties of calcium alginate fibers produced with a microfluidic device
(ELSEVIER SCI LTD, 2012) Cuadros, Teresa R.; Skurtys, Olivier; Aguilera, Jose M.
Fibers are important microstructural elements in many foods. The main objective of this research was to produce calcium alginate fibers with uniform diameters (about 300 and 550 mu m) using a microfluidic device (MFD) and to study the effect of concentration of sodium alginate [Alg] and calcium chloride [CaCl2] on their mechanical properties (MP). Moisture content (MO) and MP as maximum tensile stress (sigma(max)), tensile strain at break (Delta L/L-0) and apparent Young's modulus (E) of fibers were determined and a statistical model and surface responses were developed as a function of [Alg] and [CaCl2]. As [CaCl2] increased first a strengthening and then a weakening of fibers were observed. Furthermore, sigma(max) increased with the addition of Ca2+ and a maximum of sigma(max) was obtained for a [CaCl2] around 1.4% (exceeding several times the stoichiometric requirements of the carboxylate groups of the polymer). Such behavior prompted a molecular explanation of what happens during gelation based on the "egg-box model" and this model is tried to complete. Moreover, fibers with [Alg] >= 1.8% showed high extensibility (Delta L/L-0 around 100%) and low values of MO. High values of E (similar to 0.5 MPa) were obtained for [CaCl2] close to 1.4%. A greater understanding is needed of the interaction between cation-polysaccharide-water, taking into account [Alg] and [CaCl2] to predict the mechanical behavior of fibers. Calcium alginate fibers are important in food engineering as texture and microencapsulation agents. (C) 2012 Elsevier Ltd. All rights reserved.
Microstructure affects the rate of chemical, physical and color changes during storage of dried apple discs
(ELSEVIER SCI LTD, 2008) Acevedo, Nuria C.; Briones, Vilbett; Buera, Pilar; Aguilera, Jose M.
Blanching, freezing and drying induce major changes in the physical properties of processed foods. Microstructural changes induced by these processes in apple discs were related to the degree and kinetics of browning and to fracture mechanics after drying and later storage at 70 degrees C under a wide range of relative humidity (RH). Blanched and unblanched apple discs were dehydrated by vacuum drying or freeze-drying to induce the formation of different structures, then equilibrated from 33% to 75% RH and stored at 70 degrees C in order to promote browning. Color changes on the surface of apple discs were analyzed non-invasively by image analysis using a computerized vision system. Pre-treatments and drying conditions modified the structural characteristics of apple discs, which in turn, changed sorption properties, texture hardness and browning development. Microstructural changes (e.g., loss of cellular integrity) promoted higher browning rates, the rate and degree of browning was analyzed. (c) 2007 Elsevier Ltd. All rights reserved.
Microstructure, mechanical properties, and starch digestibility of a cooked dough made with potato starch and wheat gluten
(ELSEVIER, 2011) Parada, Javier; Aguilera, Jose M.
Processed starch-protein foods may exhibit a variety of microstructures, hence different mechanical properties and starch digestibility but the relation between these parameters is yet to be resolved. This paper reports on the effect of three processing factors (extent of mixing, cooking temperature and cooking time) on the microstructure of a model dough system consisting of potato starch, wheat gluten and water, and the in vitro digestibility of starch in the matrix as well as the relationship between microstructure and starch digestibility. Samples subjected to a high mixing level showed lower rupture stress and rupture strain (decreased by 54% and 46%, respectively), a higher residual gelatinization enthalpy of starch (Delta H), and a higher amount of birefringent starch granules (increased by 25%). Additionally, at higher mixing level the in vitro starch digestibility resulted in 24% less slowly available glucose whereas the rapidly available glucose increased by 25%. These findings were related to the original microstructure of the dough examined by confocal scanning laser microscopy. (C) 2011 Elsevier Ltd. All tights reserved.
Physical Properties and Microstructural Changes during Soaking of Individual Corn and Quinoa Breakfast Flakes
(WILEY, 2011) Medina, Wenceslao T.; de la Llera, Andres A.; Condori, Juan L.; Aguilera, Jose M.
The importance of breakfast cereal flakes (BCF) in Western diets deserves an understanding of changes in their mechanical properties and microstructure that occur during soaking in a liquid (that is, milk or water) prior to consumption. The maximum rupture force (RF) of 2 types of breakfast flaked products (BFP)-corn flakes (CF) and quinoa flakes (QF)-were measured directly while immersed in milk with 2% of fat content (milk 2%) or distilled water for different periods of time between 5 and 300 s. Under similar soaking conditions, QF presented higher RF values than CF. Soaked flakes were freeze-dried and their cross section and surface examined by scanning electron microscopy. Three consecutive periods (fast, gradual, and slow reduction of RF) were associated with changes in the microstructure of flakes. These changes were more pronounced in distilled water than in milk 2%, probably because the fat and other solids in milk become deposited on the flakes' surface hindering liquid infiltration. Structural and textural modifications were primarily ascribable to the plasticizing effect of water that softened the carbohydrate/protein matrix, inducing partial collapse of the porous structure and eventually disintegration of the whole piece through deep cracks.
Rheological and microstructural characterization of WPI-stabilized O/W emulsions exhibiting time-dependent flow behavior
(ELSEVIER SCIENCE BV, 2012) Bellalta, Pablo; Troncoso, Elizabeth; Zuniga, Rommy N.; Aguilera, Jose M.
The theological behavior of oil-in-water (O/W) emulsions stabilized by whey protein isolate (WPI) and its relationship with the microstructural changes caused by shearing was studied. O/W emulsions (50, 55, and 60 g oil/100 g) were made using ultrasound and their theological properties were determined by: flow curve test, constant shear rate test, and hysteresis loop test. Microstructural changes were evaluated in terms of droplet size and droplet size distribution. Emulsions containing 50 and 55 g oil/100 g showed a Newtonian behavior, whereas those with 60 g oil/100 g exhibited shear-thinning behavior. Under constant deformation, the apparent viscosity of the emulsions decreased with time. The hysteresis loop test revealed that increasing oil content increased the degree of thixotropy of the emulsions. Moreover, before and after the constant deformation test droplet size distributions did not show differences, indicating that the decrease in the apparent viscosity may be promoted by breakdown and further deformation and/or reorganization of oil droplets flocs. In turn, experimental data obtained from the constant shear rate test was fitted to a structural kinetic model. The rate constant values showed no particular trend with oil content and shear rate, implying that probably wall slip occurred at high shear rates and high oil contents. (C) 2011 Elsevier Ltd. All rights reserved.
Scale-sensitive Fractal Analysis of the Surface Roughness of Bloomed Chocolate
(WILEY, 2006) Briones, Vilbett; Brown, Christopher A.; Aguilera, Jose M.
The surface roughness of stored chocolate bars was studied by scanning laser microscopy and area-scale fractal analysis. Topographic data were expressed by the statistical average roughness (Sa), by two parameters from area-scale analyses-the fractal complexity (Asfc) and the scale of the rough-to-smooth transition (SRC)-and by the relative area as a function of scale. The roughness measured with Asfc showed extremely low correlation with the SRC, indicating that these two, parameters can be considered to be independent. Asfc appeared to have some correlation (R-2 = 0.82) with the Sa, indicating that for these data Asfc and Sa are somewhat related. As surface roughness (Asfc) increased during storage, gloss decreased in a linear fashion (R-2 = 0.96), which is consistent with the proposal that surface roughness is intimately related to gloss. The scales of observation from about 0.5 to 100 mu m(2) were characteristic of the fat bloom interaction with chocolate surface and with the gloss. Fractal analysis provides parameters (Asfc and relative area) that are better than conventional arithmetic mean roughness for describing the surface changes during storage of chocolate. Both the complexity (Asfc) and the relative areas showed strong correlations with gloss (0.96 and 0.94, respectively), which is consistent with a facet-based scattering model.

Browsing by Author "Aguilera, Jose M."

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