Journal Articles
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Item Formation of nano-fibrils from the A, B and C variants of bovine beta-lactoglobulin(ELSEVIER SCI LTD, 1/02/2015) Dave, AC; Loveday, SM; Anema, SG; Jameson, GB; Singh, HItem Tuning heat-‐induced colloidal aggregation of whey proteins, sodium caseinate and gum arabic: effect of protein composition, preheating and gum arabic level(ELSEVIER SCI LTD, 2014) Loveday, SM; Ye, Aiqian; Anema, Skelte G; Singh, HarjinderHeating can drive the colloidal complexation of negatively-‐charged proteins and polysaccharides by strengthening hydrophobic interactions and denaturing proteins, thereby exposing reactive sites for covalent and noncovalent bonding. We have previously shown that stable colloidal aggregates comprising whey protein, sodium caseinate and gum arabic can be produced by careful selection of heat treatment, pH and protein type. Here we tested how the size, composition, charge and morphology of colloidal aggregates are affected by the amounts of whey protein, sodium caseinate and gum arabic, as well as the thermal history of the proteins. Increasing amounts of whey protein resulted in larger particles, which were more prone to precipitate. Preheating whey protein slightly enhanced aggregation, and this effect was mitigated when sodium caseinate was present during preheating (chaperone effect). Increasing amounts of gum arabic produced larger particles with less charge, but the gum arabic effect was statistically confounded with ionic strength. We believe that both covalent (disulphide) and noncovalent interactions among protein molecules are required to overcome electrostatic repulsion at pH 7 and form stable aggregates.Item Innovative yoghurts: novel processing technologies for improving acid milk gel texture(Elsevier, 2013) Loveday, SM; Singh, Harjinder; Sarkar, AnweshaConsumers are demanding low-fat yoghurts without hydrocolloid stabilisers, but they are unwilling to compromise on texture for the sake of a ‘clean label’. Producing high quality low-fat yoghurt without stabilisers is challenging, and there is a need for new processing technologies to address consumer demand. Here we examine four technologies that can potentially improve the texture of yoghurt: high-pressure processing (HPP), high-pressure homogenisation (HPH), ultrasonic processing (USP) and protein crosslinking with the enzyme transglutaminase (TG). The benefits of HPH and USP depend on fat content, whilst HPP and TG work best in combination with other processes, and have strong potential for improving protein ingredients.Item In vitro gastric digestion of heat-induced aggregates of β-lg(Elsevier Inc., 2012) Loveday, SM; Singh, Harjinder; Ye, Aiqian; Peram, Malleswara R.An in vitro gastric digestion of heat-induced aggregates of β-lactoglobulin (β-lg) in simulated gastric fluid was investigated using sodium dodecyl sulfate-PAGE under nonreducing and reducing conditions, native-PAGE, 2-dimensional electrophoresis, and size exclusion chromatography. Heating at 90ºC significantly increased the digestibility of β-lg, with a high initial digestion rate followed by a relatively constant rate of digestion at a high enzyme:substrate (E:S) ratio of 3:1. At a low E:S ratio (1:6), the rate of digestion of β-lg was slower, and intermediate and low molecular weight species could be seen. The high molecular weight nonnative aggregates (pentamers, tetramers, trimers, etc.) were digested relatively rapidly, whereas some of the nonnative dimers were resistant to digestion and others were digested rapidly. The intermediate molecular weight species (21 to 23 kDa) were digested slowly. These results indicated that the digestibility of nonnative β-lg aggregates varied significantly depending on the E:S ratio and the types of aggregate. Further investigation is necessary to identify and characterize slowly digested dimers and intermediate molecular weight species.Item Whey protein nanofibrils: kinetic, rheological and morphological effects of group IA and IIA cations(International Dairy Journal, 2012) Loveday, SM; Su, Jiahong; Rao, M. Anandha; Anema, Skelte G.; Singh, HarjinderSelf-assembly of whey proteins into amyloid-like fibrils during heating at pH 2 and low ionic strength is sensitive to the presence of NaCl and CaCl2. Our earlier work established that at 10 - 120 mM of these salts speeds up self-assembly and favours short, flexible fibrils over long semiflexible fibrils in a way that depends on cation concentration and cation type. Here we explored how other mono- and divalent salts affected fibril morphology and the rheology of fibril dispersions. Divalent salts (MgCl2, CaCl2, BaCl2) had much stronger effects than monovalent salts (LiCl, NaCl, KCl) on gelation kinetics, and differences between salts of the same type were not large. No marked effects of salt type on fibril morphology were evident, but there were subtle differences in the size and extent of fibril networks with mono- vs. divalent salts, which may explain differences in bulk rheology.Item 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.Item 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.Item 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.Item Rheological Behavior of High-concentration Sodium Caseinate Dispersions(Wiley-Blackwell, 2010) Loveday, SM; Rao, M. A.; Creamer, Lawrence K.; Singh, HarjinderApparent 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.Item 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