Browsing by Author "Zuniga, R. N."

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Comparative study of physical and sensory properties of pre-treated potato slices during vacuum and atmospheric frying
    (ELSEVIER, 2009) Troncoso, E.; Pedreschi, F.; Zuniga, R. N.
    The objective of this research was to study the effect of different processing conditions on physical and sensory properties of potato chips. Potato slices of Desiree and Panda varieties (diameter: 30 mm; thickness: 3 mm) were pre-treated in the following ways: (i) control or unblanched slices without pre-drying; (ii) blanched slices in hot water at 85 degrees C for 3.5 min and air-dried at 60 degrees C until a final moisture content of similar to 0.6 kg water/kg dry solid; (iii) control slices soaked in a 3.5 kg/m(3) sodium metabisulphite solution at 20 degrees C for 3 min and pH adjusted to 3. Pre-treated slices were fried at 120 and 140 degrees C under vacuum conditions (5.37 kPa, absolute pressure) and under atmospheric pressure until they reached a final moisture content of similar to 1.8 kg water/100 kg (wet basis). An experimental design (3 x 2(3)) was used to analyze the effect of pre-treatment, potato variety, type of frying and frying temperature over the following responses: oil content, instrumental color and texture and sensory evaluation. Vacuum frying increased significantly (p < 0.05) oil content and decreased instrumental color and textural parameters. Sensory attributes, flavor quality and overall quality, were significantly improved using vacuum frying. The higher frying temperature (140 degrees C) increased Delta E, maximum breaking force, hardness and crispness and decreased L* and b* values. On the other hand, Panda potato variety improved the color of the product. A great improvement on color parameters was obtained using sulphited potato slices instead of the other pre-treatments. Although, the better flavor was obtained for control potato chips, no significant differences were found for overall quality between control and sulphited potato chips. Significant correlations (p < 0.01) between sensory and instrumental responses were found. (C) 2008 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved.
  • Thumbnail Image
    Item
    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.
  • Thumbnail Image
    Item
    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.
  • Thumbnail Image
    Item
    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.
  • Thumbnail Image
    Item
    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.