Browsing by Author "Diaz, Oscar"

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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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    Kinetic modeling of deterioration of frozen industrial burgers based on oxidative rancidity and color
    (2018) Quevedo, Roberto; Pedreschi Plasencia, Franco; Valencia, Emir; Diaz, Oscar; Bastias, Jose; Munoz, Ociel
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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 enzymatic browning kinetics in pear slices using non-homogenous L* color information from digital images
    (ELSEVIER SCIENCE BV, 2009) Quevedo, Roberto; Diaz, Oscar; Caqueo, Arnaldo; Ronceros, Betty; Aguilera, J. M.
    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 (BIP). 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. (C) 2009 Elsevier Ltd. All rights reserved.
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    Synthesis and coordination properties of chiral bidentate P,O-donor ligands
    (SOC CHILENA QUIMICA, 2006) Diaz, Oscar; Contreras, Raul; Valderrama, Mauricio
    Reaction of the chiral compound (S)-(+)-BrCH2CHMeCH2OH with Ph2PK in the presence of lithium diisopropylamide (LDA) and BH3/THF yields the monophosphine (S)-Ph2P(BH3)CH2CHMeCH2OH(1). The reaction of 1 with ClOSO2Me/Et2N or NaH/Mel gives rise to the formation of the general compound (S)-Ph2P(BH3)CH2CHMeCH2OR [R = SO2Me (2), Me (5)], which by treatrent with pyrrolidine affords (S)-Ph2PCH2CHMeCH2OR [R = SOMe (4), Me (6)). The monophophines 4, 6 and (S)-PPh2CH2CHMeCH2OH react with [{Cp*IrCl(mu-Cl)(2)] to give the neutral compounds [Cp*IrCl2(PPh2CH2CHMeCH2OR-P)], where only the compound with R - H (7) was fully characterized. Complex 7 reacts with AgBF4 yielding the cationic complex [Cp*IrCl(PPh2CH2CHMeCH2OH-PO)]BF4 (8) in which the ligand acts in its bidentate form. Similar synthetic results were obtained using [jCp*IrI(mu-I)(2)] as starting complex.
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    Synthesis and structure of dicarbonyldichloro{2-(diphenylphosphineoxide)pyridine}ruthenium(II)
    (SOC CHILENA QUIMICA, 2008) Diaz, Oscar; Medina, Soledad; Valderrama, Mauricio; Lahoz, Fernando J.; Martin, M. Luisa
    Reaction of the dinuclear complex [{Ru(CO)(3)Cl-2}(2)] with the ligand 2-(diphenylphosphineoxide)pyridine (PyPOPh2) in ethanol solution gave the neutral mononuclear complex [Ru(k(2)-PyPOPh2-N,O)(CO)(2)Cl-2]. The complex was characterized by elemental analysis, IR and RMN spectroscopy, and its molecular structure was determined by single-crystal X-ray diffraction.