Papers by Roberto Quevedo
Systematics Association Special Volumes, 2006
... An electronic version of this map can be obtained from the Museo Noel Kempff web site (http:/... more ... An electronic version of this map can be obtained from the Museo Noel Kempff web site (https://www. museonoelkempff. org). ... There are also Chiquitano species present in these plots, and a comparison of the floristic composition of the plots from the south-central Amazon ...
Food Science and Technology International
Food and Bioprocess Technology, 2008
Food and Bioprocess Technology, 2008
The computer vision and a stereoscopy technique were used to characterize and detect changes in t... more The computer vision and a stereoscopy technique were used to characterize and detect changes in the capacity of the salmon fillet surface to recover its original form after a constant weight was applied. A curvature index (associated to fillet firmness) calculated by means of 3D information data obtained with the stereoscopy technique from the fat stripe on the fillets was estimated over 6 months and was suggested as a characteristic of the recovery property of the fresh salmon fillet surface. Simultaneously, instrumental firmness using a LFRA1500 texture was measured. The values for the fresh salmon fillet measurement curvature index during a period of 6 months were established in the range of 0.05 and 0.10 (dimensionless), and this value was used in the experiments to represent fresh salmon fillets. Changes in the curvature index (associated with similar changes in firmness) for salmon fillet surface treated with enzymes (pepsin and papain) were registered on the second day during storage at 2°C. In general, stereoscopy is a technique that can be used on salmon fillets to detect changes in the recovery properties of the salmon fillet surface and to determine when salmon fillets can be classified as a fillet that has not been processed with enzymes.
Systematics Association Special Volumes, 2006
... An electronic version of this map can be obtained from the Museo Noel Kempff web site (http:/... more ... An electronic version of this map can be obtained from the Museo Noel Kempff web site (https://www. museonoelkempff. org). ... There are also Chiquitano species present in these plots, and a comparison of the floristic composition of the plots from the south-central Amazon ...
Food and Bioprocess Technology, 2011
This work was undertaken to analyze the ripening process of avocados variety Hass (Persea america... more This work was undertaken to analyze the ripening process of avocados variety Hass (Persea americana Mill.) by image processing (IP) methodology. A set of avocados (10 samples) was used to follow the changes in image features during ripening by applying a computer vision system, extracting color and textural parameters. Other 16 avocados were used to evaluate the firmness and mass loss. Three maturity stages of avocados were established, and a classification was obtained by applying principal component analysis and k-nearest neighbor algorithm. During the ripening process (12 days), avocado firmness decreased from 75.43 to 2.63 N, while skin color values kept invariable during 6 days; after that, a decrement in the peel green color (a*) was observed (−9.68 to 2.32). Image features showed that during ripening the color parameters (L*, a*, and b*), entropy (4.29 to 4.00), angular second moment (0.287 to 0.360), and fractal dimension (2.58 to 2.44) had a similar path as compared to mass loss, a*, and firmness ripening parameters, respectively. Relationships between image features and ripening parameters were obtained. The parameter a* was the most useful digital feature to establish an acceptable percentage of avocado classification (>80%) in three different maturity stages found. Results obtained by means of IP could be useful to evaluate, at laboratory level, the ripening process of the avocados.
Food and Bioprocess Technology, 2011
Your article is protected by copyright and all rights are held exclusively by Springer Science+Bu... more Your article is protected by copyright and all rights are held exclusively by Springer Science+Business Media, LLC. This e-offprint is for personal use only and shall not be selfarchived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".
LWT - Food Science and Technology, 2009
A ''fractal browning indicator'' (FBI) methodology is presented, describing enzymatic browning ba... more A ''fractal browning indicator'' (FBI) methodology is presented, describing enzymatic browning based on irregular color patterns from digital pear slice surface images. It uses the Fourier fractal texture images to calculate a fractal dimension (FD) value in a selected area of the image, which represents the complexity of color distribution (lightness or L * ) in the area analyzed. During the procedure, colors from digital images were first transformed to L * a * b * space color using a transformation function, in order to derivate a lightness color parameter (L * ). Experiments were carried out in three pear cultivars: Packham pear (PP); Hosui Asiatic pear (AP) and Berries Pear (BP). During the kinetics, the L * decreased when the FD increased, indicating a greater complexity in the distribution of the L * values in a selected analyzed area, during enzymatic browning kinetics, for all cultivars. The empirical power-law model was suitable for correlating enzymatic browning kinetics data both for the FBI and the traditional method (L * mean value is used). However, enzymatic browning rates for PP cultivars, using the FBI method, were 25 times higher than the rates obtained with the traditional method; and 4 times higher for other cultivars respectively. The empirical non first-order model was established for all cultivars for the FBI and traditional methods.
Journal of Plant Nutrition, 2008
Effect of foliar application of calcium (0.78 g, 4.68 g, and 7.8 g Ca) in pre-harvest, at three d... more Effect of foliar application of calcium (0.78 g, 4.68 g, and 7.8 g Ca) in pre-harvest, at three different growing conditions (tunnel, mesh, and ambient), on texture and pectin in blueberries (Vaccinium corymbosum) was studied. Calcium contents in leaves as well in fruits were different (P ≤ 0.05), affected by growing conditions and time. Differences (P ≤ 0.05) in calcium
Journal of Plant Nutrition, 2008
... a & Viviana Sepúlveda a pages 849-866. ... Proceedings of the Eighth International Congre... more ... a & Viviana Sepúlveda a pages 849-866. ... Proceedings of the Eighth International Congress on Engineering and Food. April 9 to 13 2000 , Puebla City, Mexico. Edited by: Welti-Chanes, J., Barbosa-Cánovas, G. and V y Aguilera, JM pp.16381642. Techn. Publ. Co. Inc. ...
Journal of Food Engineering, 2009
A new approach (FBI) describing the enzymatic browning kinetics for three apple cultivars, is pre... more A new approach (FBI) describing the enzymatic browning kinetics for three apple cultivars, is presented. It is based on quantification of the irregular color patterns that emerge from the apple surface during enzymatic browning, rather than using the color average in the same area analyzed. In the experiments, three apple cultivars slices were placed under a computer vision system and color digital images were captured. The images were transformed to Lab space color using a quadratic transformation function and the Fourier fractal texture image was used to calculate a fractal dimension value (FD), in order to represent the complexity of lightness intensity distribution (L) over the surface. FD (proposed method) and the mean L value (traditional method) were used indistinctly (as a fractional conversion) to model the enzymatic kinetic using the power-law model. The results showed that the fractal theory can be used to describe the browning kinetic and to distinguish apple cultivars, based on their browning sensitivity under the same experimental conditions. Enzymatic browning rates derived using the fractal kinetic method, were between 14.3 and 23.2 times (in absolute value) higher than the rates calculated with the traditional method. The fractional first-order model was established only for kinetics calculated using the traditional method.
Journal of Food Engineering, 2002
Images, particularly photomicrographs, provide qualitative information about surfaces of foods an... more 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). Ó
Journal of Food Engineering, 2008
The analysis of fractal texture reflects a change in pixel intensity, and this might contain info... more The analysis of fractal texture reflects a change in pixel intensity, and this might contain information about the structure of objects since a great change in intensity might usually indicate changes in the object. In the images of banana surfaces, the texture image can, to some extent, reflect changes and thus it can be used as an indicator of the last stage during the ripening process (over-ripening). In this experiment, bananas (Musa cavendish) were stored during 10 days at 20°C. Images of banana surfaces were recorded using a computational vision system. The over-ripening process of bananas was represented by an increment in the fractal value derived from texture fractal Fourier analysis. The result shows that fractal texture derived from the spectral Fourier analysis increased monotonically and it can be used as an indicator of the senescence process also called ''senescent spotting" of the banana peel.
Journal of Food Engineering, 2011
Modelling of browning is essential to evaluate the effectiveness of the processes applied to obta... more Modelling of browning is essential to evaluate the effectiveness of the processes applied to obtain fresh-appearance foods and also to determine their shelf life. Computer vision and the fractal kinetic method were used to quantify browning in three avocado cultivars. Samples (avocado slices and purée) were stored at 4°C and surface images were captured in the tiff format. Browning kinetic
Journal of Food Engineering, 2004
Several properties of foods, most notably visual perception and color, depend on the complexity o... more Several properties of foods, most notably visual perception and color, depend on the complexity of their outer surface. The socalled 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 (r). Rougher surfaces have higher L and r 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.
Journal of the American Oil Chemists' Society, 2005
Laser scanning microscopy and fractal analysis were used to determine roughness in the surface of... more Laser scanning microscopy and fractal analysis were used to determine roughness in the surface of chocolate samples stored under cycling temperature conditions (16 to 26°C) for 24 d. The four samples varied in the source of fat: 100% cocoa butter (CB), lauric and nonlauric fat replacers, and CB with 2% of nonlauric fat replacer. The response variable was the area-scale fractal complexity (Asfc), equivalent to a fractal dimension. Asfc increased with time to an asymptotic value (AV) in much the same way as whiteness index, both being accepted proxies of surface bloom. Images produced from topographical data revealed clearly the increase in roughness. Chocolate samples prepared with CB replacers exhibited an induction period and a slower rate of change in surface roughness than chocolate containing only CB. A linear relationship between a normalized roughness and the square root of time was followed by CB chocolate samples for the period before reaching AV. This result suggests that either diffusion or capillary flow may be the mechanism involved in fat migration to the surface.
Información tecnológica, 2007
El pretratamiento químico usado en la elaboración de pasas de arándano incrementa la velocidad de... more El pretratamiento químico usado en la elaboración de pasas de arándano incrementa la velocidad de secado. El arándano al igual que la uva posee una piel muy impermeable que no permite la transferencia de masa.
Food Science and Technology International, 2003
A slab-shaped model food prepared using glucose solutions and agar as jellifying agent was subjec... more A slab-shaped model food prepared using glucose solutions and agar as jellifying agent was subjected to drying in an experimental drier. Drying kinetics and surface temperature (ST) distribution along drying were evaluated. When fractal analysis was applied to ST distributions it was possible to observe three stages: the first one, at the beginning of the process, was very short and could not be associated with a fractal dimension. The second one, by far the longest, had a constant value of the fractal dimension of the ST distribution and towards the end of the process, as temperature of the surface of the material tended to homogenise, a final linear stage was found which corresponded to equilibrium conditions. Images of the slab along drying were recorded and showed an increasing heterogeneous appearance as drying proceeds. Grey level intensity plots corresponding to these images also showed an increasing irregularity (higher values of fractal dimension) with drying time. Fractal analysis probed to be a useful tool for describing drying kinetics and for characterising images of samples subjected to dehydration.
Food Research International, 2009
A novel methodology ''fractal browning indicator" (FBI) is presented, that describes the enzymati... more A novel methodology ''fractal browning indicator" (FBI) is presented, that describes the enzymatic browning kinetic based on the use of irregular color patterns from banana slice images. It uses the fractal Fourier texture image value in a selected area, to calculate a fractal dimension (FD), which represents the complexity of color distribution. During the procedure, colors from digital images were first transformed to L à a à b à space color using a transformation function (quadratic model), in order to derivate three color channels, lightness (L à ), redness (a à ), and yellowness (b à ). In the results, lightness and yellowness parameters decreased during the browning kinetic, when their respective FD values increased, indicating major color distribution complexity in a selected area analyzed during the kinetic. The redness color (a à ) did not show any statistical variation. The empirical power law model was suitable to correlate enzymatic browning kinetic data both for FBI and for the traditional method (when an L à mean was used). However, enzymatic browning rates using the FBI method, were between 8.5 and 35 times higher than rates calculated with the traditional method.
… proceedings from The …, 2003
In the tropical lowlands of Bolivia, indigenous peoples claim formal and official recognition of ... more In the tropical lowlands of Bolivia, indigenous peoples claim formal and official recognition of their rights to 24 million ha, and during the last decade, they have experienced considerable success. Commercial forestry is a potential on 8.3 million ha, and local indigenous communities are increasingly engaged in forest operations. Three scenarios are outlined for commercial forestry in indigenous territories: (i) sale of standing timber, (ii) own extraction of timber, (iii) own extraction and sawing of timber. Economic assessment and strategic analysis indicate increasing income and employment possibilities for the local communities if they embark on integrated commercial timber production. However, they face barriers: little competence at such production, lack of capital, and difficulties in market positioning. Formation of networks with other communities or actors in the sector may constitute a viable strategy to overcome these barriers, and a typology for different cooperative ventures is presented.
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Papers by Roberto Quevedo