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

Browsing by Author "Aguilera, J. M."

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Characterization and microstructure of films made from mucilage of Salvia hispanica and whey protein concentrate
(ELSEVIER SCI LTD, 2012) Munoz, L. A.; Aguilera, J. M.; Rodriguez Turienzo, L.; Cobos, A.; Diaz, O.
Microstructural, physical and functional properties of thin films (90-110 mu m) made from blends of the mucilage of Salvia hispanica (MC) and whey protein concentrate (WPC) were studied. Two proportions of MC:WPC were used (1:3; 1:4) at pH 7 and 10 in distilled water using glycerol as plasticizer. The effects of MC: WPC ratio and pH on colour, solubility, water vapor permeability, mechanical properties and microstructure were investigated. Transmission and scanning electron microscopy were used to investigate the microstructure of aggregates and films. Films produced at pH 10 and MC:WPC ratio of 1:3 has superior mechanical properties than the other films, with higher resistance and flexibility. Also, films produced at pH 10 demonstrated better water vapour barrier (0.620 +/- 0.08 g mm/kPa h m(2)) than films at pH 7. The pH and higher proportion of polysaccharide had a positive influence on mechanical and barrier properties achieving the highest value at pH 10 and higher proportion of polysaccharide. (c) 2012 Elsevier Ltd. All rights reserved.
Chia seeds: Microstructure, mucilage extraction and hydration
(ELSEVIER SCI LTD, 2012) Munoz, L. A.; Cobos, A.; Diaz, O.; Aguilera, J. M.
Microstructural features of the chia seeds (Salvia hispanica L.) were studied by light and scanning electron microscopy. The study reports the effect of temperature (4-80 degrees C), pH (4-8) and seed:water ratio (1:20 and 1:40) on extraction of the mucilage of chia seeds and the effect of temperature (20-80 degrees C), pH (3-9) and ionic strength (0-1%) on hydration of the extracted mucilage. The mucilage was localized in cellular structures in the first three layers of the seed coat and upon full hydration filaments (mucilage fibers) became apparent and conformed to a transparent "capsule" attached to the seed. During extraction, temperature and seed:water ratio were found to have a significant effect on yield. Hydration of the extracted mucilage was significantly increased at high pH values, and was higher when salt concentration decreased, being maximal when the temperature reached values close to 80 degrees C. (C) 2011 Elsevier Ltd. All rights reserved.
Determination of senescent spotting in banana (Musa cavendish) using fractal texture Fourier image
(ELSEVIER SCI LTD, 2008) Quevedo, R.; Mendoza, F.; Aguilera, J. M.; Chanona, J.; Gutierrez Lopez, G.
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 degrees 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. (c) 2007 Elsevier Ltd. All rights reserved.
Formation of O/W macroemulsions with a circular microfluidic device using saponin and potato starch
(ELSEVIER SCI LTD, 2009) Skurtys, O.; Aguilera, J. M.
The formation of O/W macroemulsions stabilized by a non-ionic surfactant (Quillaja saponin) and gelatinized starch was investigated using a flow focusing device consisting of circular microchannels. Droplets of hot oil (T(oil) = 338 K) were dispersed into an aqueous solution of saponin and potato starch granules. The oil fraction varied between 0.9% and 5% (dilute macroemulsions) while the starch-to-saponin concentration ratio, a, ranged between 0 and 187.5. The heat transfer from the hot oil droplet (340 to 725 mu m in diameter) induced the gelatinization of the adjacent starch granules to create a thin-shell around the oil droplet. In order to optimize the droplet generation, the physical properties of fluids were determined and the interactions between saponin and gelatinized starch granules were studied by measuring the specific conductivity. In particular, the onset, peak and end temperatures of starch gelatinization were determined. For various a, the monodispersed regime was determined by measuring the oil droplet volume V(drop). For all cases studied, Vdrop followed a power dependence with the flow rate of the aqueous phase but the exponents were different (0.65 < n < 0.9). The formation process, i.e. the dripping and jetting regime, and the generation time of oil droplets were also detailed. (C) 2009 Elsevier Ltd. All rights reserved.
Fracture properties and microstructure of low-moisture starch probes
(TAYLOR & FRANCIS INC, 2007) Castro, L.; Aguilera, J. M.
Different microstructures were induced in thin rectangular sheets of a pregelatinized starch gel by drying in an air oven at 5 different temperatures (range 65-105 degrees C) and by freeze drying. As drying temperature increased, air-dried probes (ADP) varied from thin, dense, and transparent to thick, cellular, and translucent, and the presence of larger air cells became more evident. Freeze-dried probes (FDP) were porous, white, and exhibited minimal shrinkage. Most samples exhibited a brittle-type fracture pattern in the range 0.0 < a(w) < 0.75. FDP had much higher fracture force (FF, three-point bending test) than ADP. FF increased sharply between a, 0.44 and 0.65 for ADP but not for FDP. Light and environmental electron scanning microscopy (ESEM) were used to study the morphology and microstructure of dried probes (thickness and air cells). This work suggests that drying conditions and the microstructural features derived thereof have a larger influence on fracture properties of the starchy material than the glass transition temperature.
Gloss and colour of dark chocolate during storage
(SAGE PUBLICATIONS LTD, 2007) Pastor, C.; Santamaria, J.; Chiralt, A.; Aguilera, J. M.
The appearance of chocolate is greatly affected by bloom, which occurs during storage under unfavourable conditions. This phenomenon develops due to different causes, such as poor tempering, addition of incompatible fats, incorrect cooling methods, warm or fluctuating storage temperature, etc. The effect of storage temperature (4, 20, 25 and 30 degrees C) on gloss (60 and 85 degrees angle) and colour (CIE L*a*b*) of dark chocolate bars was analysed throughout 30 days of storage. Three kinds of dark chocolate were studied: two from the same brand containing 99 and 70% cocoa, and a third one from another brand, containing 70% cocoa. Gloss change of chocolate throughout storage time followed a similar pattern in all cases: a decrease until an asymptotic value is reached, which is exacerbated at higher storage temperatures. The influence of temperature was related to the difference between storage temperature and the melting range of cocoa fat. Only when the visual fat bloom reaches a relevant level is the colour of the product affected. Changes in both optical parameters were highly-position dependant within the same sample.
Kinetics of Formation and Physicochemical Characterization of Thermally-Induced beta-Lactoglobulin Aggregates
(WILEY, 2010) Zuniga, R. N.; Tolkach, A.; Kulozik, U.; Aguilera, J. M.
The kinetics of heat denaturation and aggregation for beta-lactoglobulin dispersions (5% w/v) were studied at 3 pHs (6, 6.4, and 6.8) and at a heating temperature of 80 degrees C. Protein aggregates were characterized for hydrodynamic diameter, microstructure, and molecular weight by means of dynamic light scattering, transmission electron microscopy, and polyacrylamide gel electrophoresis, respectively. Concentration of native beta-lactoglobulin decreased with holding time and with a decrease in the pH. Apparent rate constants were calculated for beta-lactoglobulin denaturation applying the general kinetic equation solved for a reaction order of 1.5. Values of the apparent reaction rate constant k = 7.5, 6.3 and 5.6 x 10(-3) s(-1) were found for pH 6, 6.4, and 6.8, respectively. Decreasing the pH of the dispersions produced higher aggregate sizes. After a holding time of 900 s, average hydrodynamic diameters for beta-lactoglobulin aggregates at pH 6, 6.4, and 6.8 were 96, 49, and 42 nm, respectively. These results were confirmed by transmission electron microscopy images, where a shift in the size and morphology of aggregates was found, from large and spherical at pH 6 to smaller and linear aggregates at pH 6.8. beta-Lactoglobulin formed disulfide-linked intermediates (dimers, trimers, tetramers) and so on) which then formed high molecular weight aggregates. From the results obtained by DLS, TEM, and SDS-PAGE a mechanism for beta-lactoglobulin aggregation was proposed. This study shows that heat treatment can be used to produce protein aggregates with different sizes and morphologies to be utilized as ingredients in foods.
Microstructure analysis on pre-treated apple slices and its effect on water release during air drying
(ELSEVIER SCI LTD, 2011) Ramirez, C.; Troncoso, E.; Munoz, J.; Aguilera, J. M.
Microstructural studies have played an important role in the comprehensive understanding of some food phenomena that occur during drying processes. The aim of this work was to study the effect of four pre-treatments (immersion in boiling water, vacuum impregnation, freezing/thawing, and uni-axial compression) on apple microstructure characterized by cell cavities size parameter and how the changes induced by these pre-treatments can affect the water loss rate during air drying. The quantitative structure analysis showed that freezing/thawing and compression pre-treatments caused more damage on the apple structure, yielding larger cell cavities in comparison to vacuum impregnation and immersion in boiling water and control. Apple slices that were frozen/thawed, compressed and immersed in boiling water displayed the higher drying rates and diffusivity coefficients than the vacuum impregnated and control samples. These results allow concluding that disruption of the cell walls can be considered as a factor that affects the drying rate. (C) 2011 Elsevier Ltd. All rights reserved.
Phase transitions of dairy proteins, dextrans and their mixtures as a function of water interactions
(ELSEVIER SCI LTD, 2011) Hernandez, H. Gloria; Livings, S.; Aguilera, J. M.; Chiralt, A.
The water sorption behaviour and phase transitions of dairy proteins (beta-casein and beta-lactoglobulin), dextrans (dextran6 and dextran500) and their mixtures were studied at low water content. Freeze-dried polysaccharide samples containing between 20 and 80% dairy protein were equilibrated at different water activities (a(w)) between 0.11 and 0.75, at 25 degrees C. Water sorption isotherms of pure compounds and mixtures, as well as glass transition at different water activities were determined. Crystallization of polysaccharides was also investigated. BET and Gordon and Taylor equations were used to model water adsorption isotherms and glass transition temperature behaviour, respectively. Polysaccharides showed a higher water adsorption capacity than dairy proteins in the range of aw studied, which decreased with the addition of protein. The addition of beta-casein decreased the Tg values of dextran systems. This effect was attributed to water migration from beta-casein to the polysaccharide fraction following the formation of beta-casein hydrophobic interactions. Likewise, dairy proteins provoked an increase in the temperature of dextran crystallization and a decrease in the enthalpy. This effect did not reflect the increase of dextran molecular mobility in the presence of beta-casein but could be masked by other factors, like steric hindrance. The effect of dairy proteins, especially beta-casein, on the phase transitions of polysaccharides should be considered for controlling the Maillard reaction, as well as physical and chemical changes that occur during processing and storage of food systems. (C) 2011 Elsevier Ltd. All rights reserved.
Physical properties of emulsion-based hydroxypropyl methylcellulose films: Effect of their microstructure
(ELSEVIER SCI LTD, 2012) Zuniga, R. N.; Skurtys, O.; Osorio, F.; Aguilera, J. M.; Pedreschi, F.
The initial characteristics of emulsions and the rearrangement of the oil droplets in the film matrix during film drying, which defines its microstructure, has an important role in the physical properties of the emulsion-based films. The objective of this work was to study the effect of the microstructure (two droplet size distributions) and stability (with or without surfactant) of HPMC oil-in-water emulsions over physical properties of HPMC emulsion-based edible films. HPMC was used to prepare sunflower oil-in-water emulsions containing 0.3 or 1.0% (w/w) of oil with or without SOS, as surfactant, using an ultrasonic homogenizer. Microstructure, rheological properties and stability of emulsions (creaming) were measured. In addition, microstructure, coalescence of oil droplets, surface free energy, optical and mechanical properties and water vapor transfer of HPMC films were evaluated. Image analysis did not show differences among droplet size distributions of emulsions prepared at different oil contents: however, by using SOS the droplet size distributions were shifted to lower values. Volume mean diameters were 3.79 and 3.77 mu m for emulsions containing 0.3 and 1.0% without surfactant, respectively, and 2.72 and 2.71 mu m for emulsions with SOS. Emulsions formulated with 1.0% of oil presented higher stability, with almost no change during 5 and 3 days of storage, for emulsions with and without SOS, respectively. Internal and surface microstructure of emulsion-based films was influenced by the degree of coalescence and creaming of the oil droplets. No effect of microstructure over the surface free energy of films was found. The incorporation of oil impaired the optical properties of films due to light scattering of light. Addition of oil and SOS decreased the stress at break of the emulsion-based films. The replace of HPMC by oil and SOS produce a lower "amount" of network structure in the films, leading to a weakening of their structure. The oil content and SDS addition had an effect over the microstructure and physical properties of HPMC-based emulsions which lead to different microstructures during film formation. The way that oil droplets were structured into the film had an enormous influence over the physical properties of HPMC films. (C) 2012 Elsevier Ltd. All rights reserved.
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.
Structure-fracture relationships in gas-filled gelatin gels
(ELSEVIER SCI LTD, 2009) Zuniga, R. N.; Aguilera, J. M.
Food aeration has become one of the fastest growing unit operations practiced in the food industry. Dispersed air (or other gases) provides an additional phase within the gel that may accommodate new textural and functional demands. This paper addresses the relationships between structural characteristics and fracture properties of gas-filled gelatin gels (GGG), and compare these properties with those of control gelatin gels (CGG). Three gases were used in the fabrication of GGG: air, nitrogen and helium. Experimental methods to determine density, gas hold-up, bubble sizes and bubble size distributions as well as fracture properties of GGG are presented. Increasing protein concentration produced higher density, lower gas hold-up and decreased polydispersity of bubbles due to its effect on increased solution viscosity. Type of gas affected density and gas hold-up due to the different diffusivities of gases and structures (bubble size, size distribution and number of bubbles per area) formed in GGG. Fracture values increased for both GGG and CGG with increasing protein concentration for the three gases used. GGG were weaker and less ductile than CGG, the decrease in stress and strain at fracture being between 70 and 80%, and 40 and 65%, respectively. A power law relationship (sigma(f)=2.73 x 10(rho G)(-12)(4.76)) was found between the fracture stress and gel density for the three gases studied. This study shows that the presence of bubbles in gel-based food products results in unique textural properties conferred by the additional gaseous phase. (C) 2008 Elsevier Ltd. All rights reserved.
Structuring bubbles and foams in gelatine solutions within a circular microchannel device
(ACADEMIC PRESS INC ELSEVIER SCIENCE, 2008) Skurtys, O.; Aguilera, J. M.
A flow-focusing device with circular cross-section to produce monodispersed air bubbles and foams in several gelatine solutions is presented. Four flow regimes were studied by varying the gas pressure: dripping, bi-disperse bubbly, bubbly and foam flows. Bubble formation at the flow-focusing exit is discussed in detail and compared with that in rectangular microchannels. The bubble volume was shown to depend on the viscosity of the gelatine solution but not on the surface tension. For the bubbly flow, the frequency of bubble formation in this geometry was similar to that found in rectangular microchannels. For the foam flow the frequency was independent of the pressure. Study in the outlet microchannel for the bubbly and foam flows showed that the gas flow followed a power law with the applied pressure. Finally, the viscous resistance was measured and a pressure drop law was determined for each regime. (C) 2007 Elsevier Inc. All rights reserved.
Study on image analysis application for identification Quinoa seeds (Chenopodium quinoa Willd) geographical provenance
(ELSEVIER SCIENCE BV, 2010) Medina, W.; Skurtys, O.; Aguilera, J. M.
In quality control procedures of biological materials, the geographical provenance is an important information to know. Image analysis is an accessible method that can provide this data. In this work, the geographical provenance of 25 varieties of quinoa seeds, cultivated in Europe and South America was identified from 38 averaged measurements as geometric dimensions, morphological features, fractal dimensions and color features. Principal component analysis (PCA) and hierarchical cluster analysis carried out with all of data allowed to distinguish the five varieties cultivated in Europe. They were located in one sector of the tridimensional PCA scatter plot, where 75% of the variability are expressed, and in one cluster of the UPGMA dendrogram with a cophenetic correlation coefficient of 0.7. (C) 2009 Elsevier Ltd. All rights reserved.
Ultrasonic generation of aerated gelatin gels stabilized by whey protein beta-lactoglobulin
(ELSEVIER SCI LTD, 2011) Zuniga, R. N.; Kulozik, U.; Aguilera, J. M.
Dispersed air provides an additional phase within gel-type foods may accommodate new textural and functional demands. This paper addresses the effect of using whey protein beta-lactoglobulin (beta-lg), with different degrees of denaturation, as stabilizing agent in the formation of aerated gelatin gels using ultrasound as a novel method to incorporate bubbles in model foods. The heat denaturation, aggregate formation and surface properties of beta-lg dispersions were studied at three pHs (6.0, 6.4 and 6.8) and at a heating temperature of 80 degrees C. beta-Lg dispersions with four degrees of denaturation (0%, 20%, 40% and 60%) were used to stabilize bubbles generated by high intensity ultrasound in aerated gelatin gels. Experimental methods to determine gas hold-up, bubble size distributions and fracture properties of aerated gelatin gels stabilized by beta-lg (AG), as well as control gels (CG), aerated gelatin gels without beta-lg, are presented. Gas hold-up of AG peaked at a degree of denaturation of 40% when AG were fabricated using beta-lg heated at pH 6.4 and 6.8, whereas using beta-lg heated at pH 6.0 gas hold-up decreased constantly with increasing degree of denaturation. The use of beta-lg as surfactant at pH 6.8 and 6.4 reduced the bubble sizes of AG compared with CG, but no effect was observed at pH 6.0. AG showed values of stress and strain at fracture lower than CG (5.86 kPa and 0.62), probably because of the lower gas hold-up of CG. However, both type of aerated gels were weaker and less ductile than non-aerated gels, with a decrease in stress and strain at fracture for AG between 56-71% and 33-43%, respectively. This study shows that the presence of bubbles in gel-based food products results in unique rheological properties conferred by the additional gaseous phase. (C) 2010 Elsevier Ltd. All rights reserved.

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