Browsing by Author "Creamer, Lawrence K."

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    Factors Affecting Rheological Characteristics of Fibril Gels: The Case of β-Lactoglobulin and α-Lactalbumin
    (Wiley-Blackwell, 2009) Loveday, SM; Rao, M..A.; Singh, Harjinder; Creamer, Lawrence K.
    Some of the factors that affect the rheological characteristics of fibril gels are discussed. Fibrils with nanoscale diameters from β-lactoglobulin (β-lg) and α-lactalbumin (α-la) have been used to create gels with different rheological characteristics. Values of the gelation time, tc, the critical gel concentration, c0, and the equilibrium value of the storage modulus, G, such as G'inf at long gelation times, derived from experimental rheological data, are discussed. Fibrils created from β-lg using solvent-incubation and heating result in gels with different rheological properties, probably because of different microstructures and fibril densities. Partial hydrolysis of α-la with a serine proteinase from Bacillus licheniformis results in fibrils that are tubes about 20 nm in diameter. Such a fibril gel from a 10.0% w/v α-la solution has a higher modulus than a heat-set gel from a 10% w/w β-lg, pH 2.5 solution; it is suggested that one reason for the higher modulus might be the greater stiffness of α-la fibrils. However, the gelation times of α-la fibrils are longer than those of β-lg fibrils.
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    Phase and Rheological Behavior of High-Concentration Colloidal Hard-Sphere and Protein Dispersions
    (Wiley-Blackwell, 2007) Loveday, SM; Creamer, Lawrence K.; Singh, Harjinder; Rao, M. A.
    Colloidal hard-sphere particles of narrow-size distribution exhibit crystalline and glassy states beginning at the particle volume fractions φ=0.494 and φG=0.58, respectively. Dynamic rheological data on the dispersions was strongly modified to solid-like behavior as φ approached φG. In addition, cooperative motion in structural relaxation has been observed microscopically in the colloidal dispersions near the glassy state. Very high viscosities and glassy states were also found in high-concentration dispersions of sodium caseinate, and the globular proteins: bovine serum albumin and β-lactoglobulin. Viscosity models developed for hard-sphere dispersions provided reasonable predictions of relative viscosities of colloidal protein dispersions. Dispersions of food colloidal particles may be employed in studies, in which volume fraction is the thermodynamic variable, for understanding the relaxation and transport processes related to first-order and colloidal glass transitions
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    Physicochemical changes in intermediate-moisture protein bars made with whey protein or calcium caseinate.
    (Elsevier, 2010) Loveday, SM; Creamer, Lawrence K.; Singh, Harjinder; Hindmarsh, Jason P.
    This study examined model protein bars made with whey protein isolate (WPI) or calcium caseinate and stored at 20 °C for 50 days. WPI bars remained very soft and, throughout storage, confocal micrographs showed a continuous matrix containing soluble protein and increasing quantities of glucose crystals. In contrast, calcium caseinate bars had a firm texture within 1−5 days of manufacture (fracture stress 199 ± 16 Pa) and hardened progressively during storage (final fracture stress 301 ± 18 Pa). Electrophoresis showed no evidence of covalent protein aggregation, but there were substantial changes in microstructure over the first day of storage, resulting in segregation of a protein phase from a water−glucose−glycerol phase. Proton nuclear magnetic resonance (1H-NMR) relaxometry and nuclear Overhauser effect spectroscopy (NOESY) experiments showed that water migration away from protein towards glucose and glycerol occurred 10−18 h after manufacture, lowering the molecular mobility of protein. Phase separation was probably driven by the high osmotic pressure generated by the glucose and glycerol. These results confirm that the hardening of protein bars is driven by migration of water from protein to glucose and glycerol, and microstructural phase separation of aggregated protein.
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    Rheological Behavior of High-concentration Sodium Caseinate Dispersions
    (Wiley-Blackwell, 2010) Loveday, SM; Rao, M. A.; Creamer, Lawrence K.; Singh, Harjinder
    Apparent viscosity and frequency sweep (G’, G”) data for sodium caseinate dispersions with concentrations of approximately 18−40% w/w were obtained at 20°C; colloidal glass behavior was exhibited by dispersions with concentration ≥ 23% w/w. The G’−G” crossover seen in temperature scans between 60 and 5°C was thought to indicate gelation (low-temperature crossover). Temperature scans from 5 to 90°C revealed gradual decrease in G’, followed by plateau values. The gelation and end of softening temperatures of the dispersions increased with the concentration of sodium caseinate. From an Eldridge−Ferry plot, the enthalpy of softening was estimated to be 29.6 kJ mol−1.
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    Tuning the properties of b-lactoglobulin nanofibrils with pH, NaCl and CaCl2
    (Elsevier, 2010) Loveday, SM; Creamer, Lawrence K.; Singh, Harjinder; Rao, M. A.; Wang, X. L.; Anema, S. G.
    We investigated the effects of pH (1.6 – 2.4), NaCl and CaCl2 (0 – 100mM) on the kinetics of β-lactoglobulin fibril formation during heating at 80°C. The morphology of fibrils was also examined. At pH 1.8 - 2.4 fibril formation occurred slightly faster with decreasing pH. At pH 1.6 fibril formation during the growth phase occurred much faster than at any other pH. Fibril morphology was unchanged between pH 1.6 and pH 2.0. Addition of NaCl or CaCl2 accelerated fibril formation during the growth phase, and CaCl2 shortened the lag phase as well. Worm-like fibrils were seen at ≥ 60 mM NaCl or ≥ 33 mM CaCl2, and these had a persistence length which was much shorter than the long semi-flexible fibrils formed without salts. The efficiency of fibril formation can be substantially enhanced by varying pH and salt concentration.