Esra İbanoğlu

Rheological behaviour of whey protein stabilized emulsions in the presence of gum arabic

Abstract The rheological behaviour of whey protein isolate-stabilized emulsions was investigated in the presence of gum arabic (0–15 wt%). The flow behaviour of the emulsion was observed to be pseudoplastic at all gum concentrations. The increase in ionic strength reduced the magnitude of the apparent viscosity indicating that electrostatic interactions between the high molecular weight polysaccharide molecules influenced the rheology of the system. The viscosity changed with particle size and the concentration of unbound polysaccharide in the emulsion. The apparent viscosity data was described with the empirical power law equation. Temperature dependency of the viscosity was given with an Arrhenius type relationship. An empirical equation was developed for the prediction of activation energy as a function of shear rate.

Foaming behaviour of liquorice (Glycyrrhiza glabra) extract

Abstract The foaming behaviour of liquorice extract was investigated using response surface methodology with concentration (0.1–0.3 w/v%) and whipping time (5–25 s) being the independent variables. A first-order kinetics was applied for the kinetic analyses of the foam collapse and foam decay rate constants were calculated. Regression equations for predicting overrun ( O ) and foam decay rate constant ( k ) were developed. Results suggest that concentration had a significant effect ( P ⩽0.01) on overrun and foam stability. The overrun increased with concentration and whipping time. However, the effect of whipping time on O was less pronounced. Foam stability was enhanced with the increase in concentration. The foam decay rate was observed to be mainly dependent on the concentration of sample ( P ⩽0.01) and decreased with the increase in concentration. The effect of whipping time on foam stability was observed to be insignificant ( P ⩽0.01) compared with concentration. The magnitude of changes with whipping time were observed to be more pronounced for the overrun than for the stability of liquorice extract foam.

Rheological characterization of some traditional Turkish soups

Abstract The rheological behaviour of three traditional Turkish soups was studied at different temperatures (15–70 °C), using a Brookfield viscometer. Results showed that an increase in shear rate resulted in a decrease in apparent viscosity, suggesting pseudoplastic behaviour with flow indices, n, between 0.30 and 0.43. Viscosity decreased with temperature and was described by the Arrhenius equation with activation energies between 15039 and 20160 kJ mol−1.

Effects of ozone on functional properties of proteins.

The present study investigates whether the ozone treatment could be an alternative to improve some functional properties of proteins. Ozone treatment was applied on whey protein isolate and egg white proteins which have been extensively used in food products to improve textural, functional and sensory attributes. Ozone treatment of proteins was performed either in aqueous solutions or as gas ozonation of pure protein powders. Foam formation and foam stability of proteins were enhanced extensively. The solubility of proteins were reduced as influenced from the aqueous and gas ozonation medium. The reduction was more pronounced in egg white proteins. Ozone treatment affected emulsion activity of whey protein isolate negatively and reduced the emulsion stability.

Foaming behaviour of EDTA-treated α-lactalbumin

The foaming properties of partially denatured α-lactalbumin was investigated. The partially denatured state was produced by removing bound Ca2+ by treatment with ethylenediaminetetraacetic acid (EDTA) at pH 8.0 and 25°C. Surface tension measurements showed that partially denatured α-lactalbumin unfolds easily at liquid interfaces compared with the native protein. The results of foam volume and stability measurements were consistent with the results of surface tension measurements. In the presence of EDTA a considerable amount of foam was obtained at low concentrations, such as 0.1 mg/ml, and the foam stability was improved. This indicates the importance of the protein structure on the adsorption of molecules at liquid interfaces. The presence of Ca2+ also resulted in an increase in the foamability and foam stability of α-lactalbumin compared with native protein, due to the saturation of the surface charges. This shows the binding affinity of protein to Ca2+. The investigation of the effect of Ca2+ on the surface behaviour of β-lactoglobulin, another whey protein, also showed an improvement in the foaming properties of protein.

Stability and Rheological Properties of Egg Yolk Granule Stabilized Emulsions with Pectin and Guar Gum

The effects of pectin and guar gum on rheology, microstructure and creaming stability of 1% (w/v) egg yolk granule stabilized emulsions were investigated. While the addition of low amount of pectin (0.1% (w/v)) had no effect on the emulsion viscosity, the addition of 0.5% (w/v) pectin greatly increased the viscosity. Granule-stabilized emulsion without hydrocolloids reflects the pseudoplastic behavior (shear-thinning behavior with flow behavior index, n < 1.0). Hydrocolloids, especially at high concentrations, affected the viscoelastic behavior of the emulsions and both storage (G′) and loss modulus (G′′) were regarded as frequency dependent. Emulsions behaved like a liquid with G′′ > G′ at lower frequencies, and like an elastic solid with G′ > G′′ at higher frequencies. Emulsion microstructure indicated that the presence of hydrocolloids induced flocculation. Creaming stability of emulsions was enhanced by the presence of hydrocolloids and increasing hydrocolloid concentration decreased the creaming by restricting the movement of oil droplets.

Heteroprotein Complex Formation of Bovine Lactoferrin and Pea Protein Isolate: A Multiscale Structural Analysis

Associative electrostatic interactions between two oppositely charged globular proteins, lactoferrin (LF) and pea protein isolate (PPI), the latter being a mixture of vicilin, legumin, and convicilin, was studied with a specific PPI/LF molar ratio at room temperature. Structural aspects of the electrostatic complexes probed at different length scales were investigated as a function of pH by means of different complementary techniques, namely, with dynamic light scattering, small-angle X-ray scattering (SAXS), turbidity measurements, and atomic force microscopy (AFM). Irrespective of the applied techniques, the results consistently displayed that complexation between LF and PPI did occur. In an optimum narrow range of pH 5.0-5.8, a viscous liquid phase of complex coacervate was obtained upon mild centrifugation of the turbid LF-PPI mixture with a maximum Rh, turbidity and the ζ-potential being close to zero observed at pH 5.4. In particular, the SAXS data demonstrated that the coacervates were densely assembled with a roughly spherical size distribution exhibiting a maximum extension of ∼80 nm at pH 5.4. Equally, AFM image analysis showed size distributions containing most frequent cluster sizes around 40-80 nm with spherical to elliptical shapes (axis aspect ratio ≤ 2) as well as less frequent elongated to chainlike structures. The most frequently observed compact complexes, we identify as mainly leading to LF-PPI coacervation, whereas for the less frequent chain-like aggregates, we hypothesize that additionally PPI-PPI facilitated complexes exist.

Effects of Ultrasonication and Aqueous Ozonation on Gelatinization and Flow Properties of Potato Starch

ABSTRACT Ultrasonication and aqueous ozonation were applied to potato starch simultaneously. Flow properties (i.e., flow behavior index, n; consistency index, K; and apparent viscosity, ηapp) of samples were determined using a rheometer. A differential scanning calorimeter (DSC) was used to measure the gelatinization properties of samples (onset, peak and conclusion gelatinization temperatures and enthalpy of gelatinization). Results showed that ozonation caused a significant increase (p < 0.05) in onset gelatinization temperature (from 54.9 to 59.1 °C) and a significant decrease (p < 0.05) in enthalpy of gelatinization (from 14.6 to 12.2 J/g). There were no significant differences (p < 0.05) between the consistency index (ranged from 4.57 to 4.87 Pas) and apparent viscosity (ranged from 0.10 to 0.13 Pas) of samples treated with ozonation and ultrasonication with no regards of treating sequence. This showed that the order of treatment (i.e., ozonation and ultrasonication) does not have any significant effect on the flow properties of potato starch studied under the conditions applied in this research.

Combined effect ozonation and ultrasonication on rheological and thermal properties of rice starch in aqueous phase

A combination of ozonation and ultrasonication was applied to rice starch in aqueous phase. A Bohlin rheometer was used to obtain flow behaviour and consistency indices. A differential scanning calorimeter was used to measure the gelatinisation properties (onset, peak and conclusion gelatinisation temperatures and enthalpy of gelatinisation). It was observed that all starch samples exhibited non-Newtonian behaviour (i.e. n<1). The highest viscosity values (i.e. 0.5 Pa.s) and the highest shear-thinning effect (i.e. n=0.4) were observed for ultrasonicated starch sample. The consistency index for native rice starch increased after ultrasonication. There were no significant differences (P<0.05) between the consistency index and apparent viscosity of samples treated with ozonation and ultrasonication with no regards of treating sequence. This showed that the order of treatment (i.e. ozonation and ultrasonication) does not have any significant effect on the flow properties of rice starch studied under the condi...