Browsing by Author "Kulozik, U."

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    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.
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    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.