Browsing by Author "Quevedo, Roberto"

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    Characterizing the Variability of Enzymatic Browning in Fresh-Cut Apple Slices
    (2014) Quevedo, Roberto; Valencia, Emir; Lopez, Patricia; Gunckel, Erna; Pedreschi, Franco; Bastias, Jos
    Browning reaction variability in apple slices was characterized using a new procedure denominating the differential pixel method. Using this method, a kinetic rate and an empirical order of reaction were derived for each pixel in an image corresponding to a sliced apple surface undergoing browning; each pixel in the image can be seen as a small portion of the fruit. In the experiments, 40 samples of fresh-cut apple slice were put on a computer vision system and images recorded over time at a room temperature of 5 A degrees C. Data was fitted to the Weibullian model kinetic. Results confirmed strong heterogeneity in the values of enzymatic browning kinetic rate on the apple surface; this variability was characterized as a normal logarithmical distribution, with a mean rate kinetic value of the -0.0117 A +/- 0.0036 units of L* decayed per minute. The empirical order of reaction was distributed on the surface following a normal statistical distribution with a mean equal to 0.451 A +/- 0.046. No statistical differences were established in the kinetic rate and in the empirical order when the differential pixel method was compared with the traditional method (where a mean of the L* intensity value was used).
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    Description of the kinetic enzymatic browning in banana (Musa cavendish) slices using non-uniform color information from digital images
    (ELSEVIER, 2009) Quevedo, Roberto; Diaz, Oscar; Ronceros, Betty; Pedreschi, Franco; Miguel Aguilera, Jose
    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*a*b* space color using a transformation function (quadratic model), in order to derivate three color channels, lightness (L*), redness (a*), and yellowness (b*). 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*) 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* 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. (C) 2009 Elsevier Ltd. All rights reserved.
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    Quantification of enzymatic browning in apple slices applying the fractal texture Fourier image
    (ELSEVIER SCI LTD, 2009) Quevedo, Roberto; Jaramillo, Marcela; Diaz, Oscar; Pedreschi, Franco; Miguel Aguilera, Jose
    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. (c) 2009 Elsevier Ltd. All rights reserved.
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    Quantification of the Browning Kinetic on Pita Bread Using Fractal Method
    (2018) Quevedo, Roberto; Rojas, Richard; Pedreschi Plasencia, Franco; Bastías, José Miguel; Siché, Raúl; Uquiche, Edgar; Silva, David; Díaz, Oscar