DSpace Angular :: Browsing by Author "Aguilera, JM"

Browsing by Author "Aguilera, JM"

Now showing 1 - 20 of 31

Antioxidant activity of crude extract, alkaloid fraction, and flavonoid fraction from boldo (Peumus boldus Molina) leaves
(2004) Quezada, N; Asencio, M; del Valle, JM; Aguilera, JM; Gómez, B
Boldo is an endemic plant from Chile widely used in folk medicine, whose biological (mainly antioxidant) activity has been attributed to the presence of the alkaloid boldine. The aim of this study was to determine the contribution of the flavonoid and other crude fractions from boldo leaves to the antioxidant activity of extracts. The main constituent in the flavonoid fraction was also isolated. The antioxidant activity and reducing power of crude boldo extract and fractions were measured and compared with natural and synthetic antioxidants. The antioxidant activity of boldo leaf extracts came mainly from the flavonoid fraction (44.1%) followed by the alkaloid fraction (15.6%), with catechin and boldine being the main contributors of the antioxidant activity of these 2 fractions (60.9% and 35.6% of the total activity, respectively). On the basis of these results, we propose to use catechin and boldline as markers for the antioxidant activity of boldo leaves. Tailor-made antioxidants to be used in foods can be prepared by enriching these 2 fractions.
Application of image analysis for classification of ripening bananas
(WILEY, 2004) Mendoza, F; Aguilera, JM
A computer vision system was implemented to identify the ripening stages of bananas based on color, development of brown spots, and image texture information. Nine simple features of appearance (L* a*, b* values; brown area percentage, number of brown spots per cm(2); and homogeneity, contrast, correlation: and entropy of image texture) extracted from images of bananas were used for classification purposes. Results show that in spite of variations in data for color and appearance, a simple classification technique is as good to identify the ripening stages of bananas as professional visual perception. Using L* a*, b* bands, brown area percentage, and contrast,it was possible to classify 49 banana samples in their 7 ripening stages with an accuracy of 98%. Computer vision shows promise for online prediction of ripening stages of bananas.
Applications of microprobe Raman spectroscopy in food science
(SAGE PUBLICATIONS LTD, 2002) Celedon, A; Aguilera, JM
The Raman microprobe combines the analytical properties of Raman spectroscopy and the visualization capabilities of a high quality microscope, allowing localization and identification of species and phases in time intervals of seconds to a few minutes with a spatial resolution down to 1 mum. This article describes the basic principles of operation of the Raman microprobe and some applications that are important in food technology: in situ differentiation between sucrose and lactose crystals and of amorphous and crystalline phases in sucrose; detection of semi-crystalline and gelatinized zones in starch granules, and phase transitions in cocoa butter after heating (melting)/cooling (crystallization) cycles. Extensions of these applications cover the entire range of food constituents.
Assessment of the quality of heated oils by differential scanning calorimetry
(AMER CHEMICAL SOC, 1998) Gloria, H; Aguilera, JM
Differential scanning calorimetry (DSC) was used to follow changes in the thermal characteristics of commercial frying oils (sunflower seed, colza, and groundnut) during heating at 180 degrees C for up to 10 h. DSC tracings of oils scanned from 10 to -80 degrees C were characterized by a single crystallization peak (CP) at -43 to -48 degrees C. Heating of oils resulted in a progressive shift of the CP to lower temperatures and reduced enthalpies of crystallization (EC). The temperature of the CP decreased as much as 27 degrees C, and the EC was reduced by almost 90% after heating for 10 h. These changes in thermal characteristics correlated well with the appearance of polar compounds, the increase in viscosity, and color changes of the oil. DSC is a fast method of analysis, requires small samples (15-60 mg) with minimal preparation, and may be implemented directly in fried products.
Characterization of food surface roughness using the glistening points method
(ELSEVIER SCI LTD, 2004) Quevedo, R; Aguilera, JM
Several properties of foods, most notably visual perception and color, depend on the complexity of their outer surface. The so-called 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 (sigma). Rougher surfaces have higher L and sigma 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. (C) 2003 Elsevier Ltd. All rights reserved.
Characterization of food surfaces using scale-sensitive fractal analysis
(FOOD NUTRITION PRESS INC, 2000) Pedreschi, F; Aguilera, JM; Brown, CA
Length-scale and area-scale analyses, two of the scale-sensitive fractal analyses performed by the software Surfrax www.surfract.com, were used to study food surfaces measured with a scanning laser microscope (SLM). The SLM measures surfaces, or textures (i.e., acquires topographical data as a collection of heights as a function of position), at a spatial and vertical resolution of 25 mu m. The measured textures are analyzed by using linear and areal tiling (length-scale and area-scale analysis) and by conventional statistical analyses. Area-scale and length-scale fractal complexities (Lsfc and Asfc) and the smooth-rough crossover (SRC) are derived from the scale-sensitive fractal analyses. Both measures proved adequate to quantify and differentiate surfaces of foods (e.g., chocolate and a slice of bread), which were smooth or porous to the naked eye. Surfaces generated after frying of potato products (e.g., potato chips and French fries) had similar values of Asfc and SRC, and larger (implying more complex and rougher surfaces) than those of the raw potato. Variability of surface texture characterization parameters as a function of the size of the measured region was used in selecting the size of the measured regions for further analysis. The length-scale method of profile analysis (also called the Richardson or compass method) was useful in determining the directionality or lay of the anisotropic texture on food surfaces.
Characterization of the surface properties of chocolate using scale-sensitive fractal analysis
(TAYLOR & FRANCIS INC, 2002) Pedreschi, F; Aguilera, JM; Brown, CA
A scanning laser microscope was used at its highest resolution (25 mum) to study the surface of three kinds of commercial chocolate. Data of measured surfaces were analyzed by scale-sensitive fractal analysis (SSFA) using linear and area tiling (length-scale and area-scale analysis) and by conventional statistical analyses for roughness. Area-scale and length-scale fractal complexities (Lsfc and Asfc) and the smooth-rough crossover (SRC) derived from SSFA proved adequate to characterize the surface roughness of chocolate and changes in topography as a result of bloom. The three chocolate surfaces analyzed had similar values of Asfc, Lsfc and ARa. Nestle milk chocolate presented significant higher values of SRC than those corresponding to the other two kinds of chocolate analyzed (e.g., 0.051 mm(2) vs. 0.038 and 0.037 mm(2) in the case of area-scale sensitive analysis) implying a rougher surface.
Classification of potato chips using pattern recognition
(WILEY, 2004) Pedreschi, F; Mery, D; Mendoza, F; Aguilera, JM
An approach to classify potato chips using pattern recognition from color digital images consists of 5 steps: (1) image acquisition, (2) preprocessing, (3) segmentation, (4) feature extraction, and (5) classification. Ten chips prepared for each of the following 6 conditions were examined: 2 pretreatments (blanched and unblanched) at 3 temperatures (120 degreesC, 150 degreesC, and 180 degreesC). More than 1500 features were extracted from each of the 60 images. Finally, 11 features were selected according to their classification attributes. Seven different classification cases (for example, classification of the 6 classes or distinction between blanched and unblanched samples) were analyzed using the selected features. Although samples were highly heterogeneous, using a simple classifier and a small number of features, it was possible to obtain a good performance value in all cases: classification of the 6 classes was in the confidence interval between 78% and 89% with a probability of 95%.
Crystallization kinetics of lactose in sytems co-lyofilized with trehalose. Analysis by differential scanning calorimetry
(2001) Mazzobre, MF; Soto, G; Aguilera, JM; Buera, MP
The objective of the present work was to study by differential scanning calorimetry phase/state transitions in model systems of amorphous lactose and lactose co-lyophilized with trehalose. The obtained parameters, such as glass transition temperatures (T-g) and enthalpies of crystallization were employed to test the applicability of different proposed models to predict the behavior of these systems. Thermograms of low moisture lactose-trehalose mixtures showed only one glass transition temperature indicating that compatibility exists between both sugars. The increase of trehalose concentration in the mixture promoted a delay of lactose crystallization in isothermal runs, and of the crystallization temperature (T-cr) in dynamic experiments. The presence of trehalose delayed lactose crystallization, without affecting the T-g value. Several factors (thermodynamic, geometric, kinetics) may modify the molecular environment in the combined systems, affecting nucleation and/or crystal growth. Three models [Arrhenius, Williams-Landel-Ferry (WLF) and Vogel-Tamman-Fulcher (VTF)] were used to study the temperature dependence of the crystallization time. Although experimental points were fitted fairly well by all these models in the range of temperature from 14 to 59 degreesC above T-g value, the VTF equation appears to apply better for sugars. (C) 2001 Elsevier Science Ltd. All rights reserved.
Description of food surfaces and microstructural changes using fractal image texture analysis
(ELSEVIER SCI LTD, 2002) Quevedo, R; Carlos, LG; Aguilera, JM; Cadoche, L
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). (C) 2002 Elsevier Science Ltd. All rights reserved.
Determination of kinetics of gelation of whey protein and cassava starch by oscillatory rheometry
(ELSEVIER SCIENCE BV, 1997) Aguilera, JM; Rojas, GV
Kinetics of heat-induced gelation of cassava starch (CS) suspensions, whey protein isolate (WPI) solutions and mixed blends at 10% total solids (TS) were followed by small deformation oscillatory shear rheometry in the temperature range 70-90 degrees C. Storage moduli (G') of WPI solutions (4-14% TS) increased steadily following simple first order kinetics. G' of CS suspensions (8-14% TS) increased rapidly to a peak and decayed steadily later. A model consisting of a two-step reaction with a reversible step was proposed for gelation of CS. G' of WPI gels were two orders of magnitude higher than those of CS. Mixed gels having a starch fraction = 0.2 had G' similar to those of pure WPI gels. (C) 1998 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd.
Determination of oil in fried potato products by differential scanning calorimetry
(AMER CHEMICAL SOC, 1997) Aguilera, JM; Gloria, H
Differential scanning calorimetry (DSC) was used to determine the oil uptake of commercial frozen par-fried potatoes after frying at 180 degrees C in colza/soybean oil. The enthalpy and temperature range of the crystallization peak for the pure frying oil were 47.2 J/g and -44 to -50 degrees C, respectively. DSC was performed by cooling samples of crust and core of fried potatoes from 10 to -60 degrees C at 1 degrees C/min and the oil content calculated from the peak area. The crust contained almost 6 times as much oil as the central core (23.6% vs 4%, dry weight basis), as visualized by light microscopy. Only 87% of the oil in the intact crust can be removed by solvent extraction, the rest being extractable only after grinding. Deviation between DSC and Soxtec extraction methods was less than 3%. The DSC method is fast, specific, and reliable, does not use solvents, requires smaller samples (<100 mg) than conventional solvent extraction methods, and can also detect freezable water.
Differential scanning calorimetry of low-moisture apple products
(1998) Aguilera, JM; Cuadros, TR; del Valle, JM
Differential scanning calorimetry (DSC) was used to detect thermal phase transitions in low-moisture apple products, cell walls and related materials. Freeze-dried (FD) apple tissue equilibrated over P2O5 exhibited a T-g around 11 degrees C, similar to that of FD apple juice and slightly higher than the predicted value for the sugar mixture in juice (7 degrees C). Samples also showed an endothermic peak around 50-70 degrees C. Cell wall (CW) material from apple prepared by five different methods and dried over P2O5 showed an endothermic peak (onset around 120 degrees C and peak between 130-160 degrees C) caused by water evaporation. No glass transition was detected in CW preparations for any water activity. The same behavior was observed for microcrystalline cellulose, apple pectin, pine wood and walnut leaves equilibrated over P2O5 Low-moisture CW exhibited a more hydrophobic behavior than apple tissue as revealed by adsorption isotherms. (C) 1998 Elsevier Science Ltd. All rights reserved.
Effect of kappa-carrageenan on the gelation of horse mackerel (T-murphyi) raw paste surimi-type
(SAGE PUBLICATIONS LTD, 2004) Ortiz, J; Aguilera, JM
Gelation of fresh (unfrozen) raw surimi-type paste (RS paste) from horse mackerel (T murphyi) was studied in the presence Of kappa-carrageenan (0.5, 1, 2% Ckappa) and KCl (0.5-2%) as a substitute for NaCl. Gelation was traced by measuring the storage modulus (G') during heating-cooling cycles. Variations in G' during the heating stage of the mixed system RS-Ckappa characterised the presence of a phase separation in this stage due to Ckappa solubilitation (at about 50degreesC) as well as to RS gelation (35-80degreesC) in the mixture. It was also observed that when Ckappa was added as a single ingredient. it inhibited RS gelation as a function of its concentration (>2%). Nevertheless, during the cooling stage, the final G' value for the RS-2% Ckappa mixed system was greatly increased. This reinforcing would be caused by further (cold) Ckappa gelation in the mixture. It is theorised that Ckappa might act by forming 'packed' microgels within the RS protein gel network, which is favoured upon application of a moderate (40degreesC, 60 min) thermal treatment rather than when an extreme (90degreesC, 20 min) treatment is applied. On the other hand, although KCl enhanced gelation of the 2% Ckappa solution, addition of this salt to the RS-2% Ckappa mixture did not improve its gelation. Rheological information was complemented with observation of the resulting structures by scanning electronic microscopy (SEM).
Glass transition temperature (T-g) and water activity (a(w)) of dehydrated apple products
(WILEY-BLACKWELL, 1999) Welti Chanes, J; Guerrero, JA; Barcenas, ME; Aguilera, JM; Vergara, F; Barbosa Canovas, GV
The onset glass transition temperature (T-go) of Granny Smith apple products was evaluated as a function of drying conditions (air drying and freeze-drying) and moisture and water activity (a(w)) levels. T-go was determined in the 0-0.75 a(w) range, and it was found to have a maximum value at a(w) = 0 (T-go = 4.5 +/- 1.6C) for freeze-dried apple and a minimum value at a(w) = 0.75 (T-go = -81.4 rt 0.1C) for freeze-dried apple juice. A linear relationship between T-go and a(w) was obtained in all cases. Theoretical T-go values at a(w) = 0 were calculated using these equations, and were within the range of 3.0C (freeze-dried apple) and 10.5C (apple dehydrated at 30C). When Gordon and Taylor's linear model was applied to the experimental data of all the apple products, K values within the range 2.4 (freeze-dried apple juice) and 3.6 (apple dehydrated at 60C), and the theoretical T-g of solids values at a(w) = 0 between the range -16.3C (freeze-dried apple juice) and -1.9C (apple dehydrated at 60C) were obtained. No effect of the type of drying on the value of T-g was detected.
Glass transitions and shrinkage during drying and storage of osmosed apple pieces
(ELSEVIER SCIENCE BV, 1998) del Valle, JM; Cuadros, TRM; Aguilera, JM
The relationship between shrinkage during drying and 'glass'-'rubber' transitions of apple tissue was studied. Our results did not indicate that structural collapse of apple pieces can be reduced by diminishing the difference Delta T between drying temperature and glass transition temperature (T-g) of the fruit matrix. Apple shrinkage was not consistently depressed by reducing drying temperature, infusing larger amounts of T-g-depressing agents (sucrose, maltose, lactose) or infusing similar amounts of solutes with higher anhydrous T(g)s. However, sugars added during osmotic dehydration pretreatments help decreasing structural collapse during subsequent air drying, which was reflected by a 20-65% increase in final volume of samples treated with 50% sucrose and maltose solutions as compared to an air-dried, control sample. Dried samples remained in the "rubbery" state after drying and shrunk during subsequent storage. (C) 1999 Published by Elsevier Science Ltd on behalf of the Canadian Institute of Food Science and Technology. All rights reserved.
Induction of trehalose in spores of the biocontrol agent Trichoderma harazianum
(1997) Pedreschi, F; Aguilera, JM; Agosin, E; SanMartin, R
Spores of the biocontrol agent Trichoderma harzianum P1 produced in liquid media and harvested in the stationary sporulation stage SSS (after 60 h), had higher viability after slow (>4x) and fast drying (>12x) than their counterparts harvested in the exponential sporulation stage, ESS (after 30 h). The trehalose content of SSS spores was almost 20x higher than that of ESS spores (0.16 vs. 3.4 mg/100 mg, respectively). Heat shock (40 degrees C x 90 min) effectively increased the trehalose content 2.5x with respect to untreated SSS spores. The trehalose content achieved in heat-treated SSS spores was almost 60% higher than the maximum reached by holding the spores under water-stress at 97% relative humidity prior to drying.
Limpness of fried potato slabs during post-frying period
(WILEY, 2005) Miranda, ML; Aguilera, JM; Beriestain, CI
The rupture stress (RS) of fried potato slices (1.60 mm thick) and of the crust of fried potato slabs (FPS) having lengths of 60 mm and sides of 8, 10 and 12 mm, was determined during the post-frying period by a puncture test. The RS of fried potato slices decreased as water activity increased from 0.22 to 0.85. The RS of FPS diminished in the first 5-6 min when exposed to ambient conditions and remained almost constant thereafter A novel videotape technique and image analysis were used to follow deflection of FPS in the post-frying period. An apparent modulus based on the composite structure of FPS and calculated from beam mechanics decreased with time in a trend similar to that of the textural parameters. We concluded that changes in physical properties of the crust because of moisture accumulation are the major causes of loss of texture (limpness) in FPS during the post-frying period.
Microscopy and calorimetry as complementary techniques to analyze sugar crystallization from amorphous systems
(2003) Mazzobre, MF; Aguilera, JM; Buera, MP
A comparison of microscopic and macroscopic techniques to evaluate sugar crystallization kinetics is presented using amorphous lactose and lactose-trehalose mixtures. Polarized light video microscopy (PLV) and differential scanning calorimetry (DSC) were applied to measure crystallization kinetics, induction times and time for complete sugar crystallization at different storage temperatures (60-95 degreesC). DSC was also employed to measure the glass transition temperature (T-ag) of the systems. PLV permitted direct observation, in real time, of growth of individual crystals and morphological aspects at a scale not detected by DSC. Taking the average of several microscopic observations, the results for temperature dependence of crystallization rate and time to complete lactose crystallization were similar to those obtained by DSC. Both PLV and DSC techniques showed that the presence of trehalose delayed lactose crystallization, without affecting the T;,g value. For the analysis of sugar crystallization in amorphous systems, PLV and DSC proved to be complementary techniques. Validation of results obtained by PLV with results from DSC opens a new area of microstructural analysis of crystallizing systems. (C) 2003 Elsevier Science Ltd. All rights reserved.
Microstructural changes of potato cells and starch granules heated in oil
(ELSEVIER SCIENCE BV, 2001) Aguilera, JM; Cadoche, L; Lopez, C; Gutierrez, G
A method that mimics the frying operation was implemented to observe microstructural changes in potato cells and starch. Isolated cells were obtained by successive treatments of potato tissue with acid and alkali solutions. Potato cells were heated in oil at a rate of 40 degreesC/min or directly in hot oil (180 degreesC) using a hot stage attached to a light microscope and studied by video-microscopy. Starch granules in cells underwent rapid gelatinization, deformation and compaction into one mass that occupied the whole volume of the cell. After dehydration cells showed a distinctive outer zone and a homogeneous core. Cell walls showed no signs of disruption but at temperatures > 100 degreesC a reduction in cell area occurred. Immersion of cells in hot oil resulted in rapid swelling of starch. Relative projected area increased by 12% after 45 s of heating. Wet isolated starch granules began to expand and gelatinize at 65 degreesC and became disrupted at 120 degreesC. No changes were observed in dry starch granules subjected to a similar treatment. (C) 2001 Elsevier Science Ltd. All rights reserved.

Browsing by Author "Aguilera, JM"

Results Per Page

Sort Options