Rheological characterization and electrokinetic phenomena of charged whey protein dispersions of defined sizes

A multi-step processing technique produced large colloidal particles from whey proteins, prompting instantaneous thickening upon hydration. Analysis of the rheological characteristics and zeta potential of the modified whey suspensions of defined particle sizes allowed investigation into the role of size on ingredient functionality. Preliminarily, the modified protein powders were sieved to achieve three size ranges, and analyzes were conducted on each of the three distributions and the non-sieved fractions. Following hydration, steady and oscillatory shear analyzes were performed using a controlled stress rheometer to determine rheological characteristics. Intrinsic viscosity was determined with a capillary viscometer and application of the Huggins equation. Zeta potential was calculated from colloidal electrophoretic mobility, measured with a ZetaPALS analyser. After thorough hydration, particle-size analysis revealed a size increase of >1.3 times for each fraction. When analysed on a protein basis, increasing particle size yielded an increase to intrinsic viscosity, flow behavior index, zero shear viscosity, and a decreased zeta potential and consistency coefficient. Knowledge of the interrelationship between zeta potential, rheological properties, and particle size of the modified whey ingredient will further advance an understanding of the functionality of this protein ingredient.     

Connection between rheological parameters and colloidal interactions of a soy protein suspension

The viscosity of a 9.1% (w/w) aqueous suspension of soy proteins at pH 7.5, which constitutes a colloidal dispersion of negatively charged and hydrated particles, is analyzed in relation to colloidal interactions. An experimental study is carried out through the classical shear rate rheometry, in the range 20–50°C. Viscosity data at different temperatures and shear rates are superimposed onto a master plot, which shows the characteristic shear-thinning behavior of colloidal suspensions. A microstructural model for the low shear limit viscosity is derived to establish a quantitative relationship between the viscosity and the interparticle forces in the suspension. Apart from the electrical forces, the hydration repulsive force must be considered in the calculation of the protein–protein interaction energy, in order to achieve a satisfactory prediction of the high viscosity values obtained experimentally. It is also observed that the relaxation time associated to small shear deformations differs from the characteristic relaxation time of the steady shear flow. The theoretical analysis carried out in this work explains the effect of colloidal interactions on rheological parameters of the soy protein suspension.     

Particle size effects in colloidal gelatin particle suspensions

This paper describes the effects of simple shear flow on the formation and properties of colloidal gelatin particle suspensions. Microscopy and light scattering show that simple shear flow of a phase-separating gelatin-dextran mixture gave smaller particles with a narrower size distribution. Upon gelation due to a temperature decrease, the viscosity of the gelatin increased, which altered the coalescence and break-up behaviour of the particles formed. The small particles obtained by a high shear during processing aggregated into larger particle clusters, once particle solidified upon gelation. The particle size can be predicted using correlation with droplet break-up and coalescence considering the properties before gelation. The sizes of the clusters can be predicted with the coalescence behaviour using the properties after gelation. Clusters originating from small particles resist more deformation, resulting in pronounced rheological effects (e.g. increase viscosity, increased strain softening point).     

Relation Between Particle Properties and Rheological Characteristics of Carrot-derived Suspensions

The effect of particle properties on the rheological behaviour of carrot-derived suspensions was investigated systematically. Hereto, a range of relatively monodisperse suspensions, with varying average particle sizes (～73, 176, 262 and 369 μm) and pulp contents (from 30 to 65 wt.%), was prepared by the reconstitution of carrot tissue particles in water. Suspensions with average particle size of ～73 μm consisted of cell fragments, whereas suspensions with larger particle sizes contained mainly cell clusters of which the cell number increased with increasing particle size. The rheological characteristics showed that the carrot-derived suspensions have a non-Newtonian behaviour with a yield stress, depending on particle concentration, size and type. The network structure of all suspensions could be described as a weak gel. Increase in yield stress and storage modulus with particle concentration could be fitted to a power law model. A unique linear relation was found between the yield stress and the plateau modulus, independent of the particle size and type. Particle concentration, size and type appeared to be key structural parameters controlling the rheology of these carrot-derived suspensions. When comparing the rheological behaviour of the reconstituted suspensions with the original carrot purée of similar average diameter and pulp content, the network structure (measured as yield stress or storage modulus) in carrot purée was weaker, which may be attributed to the broader particle size distribution.     

Functional Characterization of Steam Jet-Cooked β-Glucan-Rich Barley Flour as an Oil Barrier in Frying Batters

ABSTRACT:  The effect of steam jet-cooking on the hydration, pasting, and rheological properties of barley flour was investigated. The thermo-mechanical shear during steam jet-cooking led to significant increases in the water absorption, water solubility, and swelling power of the barley flour. Also, the pasting profile showed elevated initial viscosity and reduced final viscosity. In addition, the suspensions of the steam jet-cooked barley flour demonstrated typical shear thinning and dynamic viscoelastic responses of random coil polysaccharides with entanglements. The steam jet-cooked barley flour was also evaluated as an oil barrier in fried foods. Its incorporation into frying batters increased batter pickup and viscosity while the moisture loss of fried batters was reduced. These combined effects significantly lowered the oil uptake of batters.     

Modifications in stability and structure of whey protein-coated o/w emulsions by interacting chitosan and gum arabic mixed dispersions

The influence of chitosan and gum arabic mixtures on the behaviour of o/w emulsions has been investigated at pH = 3.0. The emulsion behaviour, properties and microstructure were found to be greatly dependent on the precise gum arabic to chitosan ratio. Mixing of gum arabic with chitosan leads to the formation of coacervates of a size dependent on their ratio. Incorporation of low gum arabic to chitosan weight ratios into whey protein-coated emulsions causes depletion flocculation and gravity-induced phase separation. Increasing the polysaccharide weight ratio further, a droplet network with a rather high viscosity (at low shear stress) is generated, which prevents or even inhibits phase separation. At even higher gum arabic to chitosan ratios, the emulsion droplets were immobilised into clusters of an insoluble ternary matrix. Although the emulsion droplet charge had the same sign as that of the coacervates, clusters of oil droplets in a ternary matrix were generated. A mechanism to explain the behaviour of the whey protein-stabilised o/w emulsions is described on the basis of confocal and phase contrast microscopic observations, rheological data, zeta potential measurements, particle size analysis and visual assessment of the macroscopic phase separation events.     

Effect of freezing on the viscoelastic behaviour of whey protein concentrate suspensions

The effect of freezing on viscoelastic behaviour of whey protein concentrate (WPC) suspensions was studied. Suspensions with total protein content of 5% and 9% w/v were prepared from a commercial WPC (unheated suspensions). A group of unheated suspensions was treated at two temperatures (72.5 and 77.5 °C) during selected times to obtain 60% of soluble protein aggregates (heat-treated suspensions). Unheated suspensions and heat-treated suspensions were frozen at −25 °C (frozen unheated and frozen heat-treated suspensions). Frequency sweeps (0.01–10 Hz) were performed in the region of linear viscoelasticity at 10, 20, 30, 40, and 50 °C. Mechanical spectra of all studied suspensions at 20 °C were similar to viscoelastic fluids and complex viscosity increased with the frequency (ω). Elastic (G′) and viscous (G″) moduli were modelled using power law equations (G′ = aω^x, G″ = bω^y), using fitted parameters a, x, b, and y for statistical analysis. Exponent y was the most influenced by freezing, indicating the existence of a higher degree of arrangement in frozen unheated suspensions and a lower degree of arrangement in frozen heat-treated suspensions. Only characteristic relaxation times (inverse of the crossover frequency) of suspensions with 5% w/v of total protein content were significantly influenced by freezing. Time–temperature superposition was satisfactory applied in unheated whey protein concentrate suspensions only in the range of high temperatures (30–50 °C). However, this principle failed over the complete temperature range in most of the frozen suspensions. It is possible that freezing produced an increase in the susceptibility to morphological changes with temperature during the rheological measurements.     

Rheology of Concentrated Tomato-Derived Suspensions: Effects of Particle Characteristics

In the present work, the effect of particle properties on the rheological behaviour of tomato-derived suspensions was investigated systematically. Hereto, a range of relatively monodisperse suspensions, containing either cell fragments or single cells with varying average particle size (～148, 267, 303 and 393 μm) and pulp content (from 25 to 60 wt.%), was prepared by the reconstitution of tomato tissue-based particles in water. The effect of the presence of a serum phase on the rheological properties of tomato-derived suspensions was investigated by the comparison of the rheology of reconstituted tomato purées in water with those in serum. All the tomato-derived suspensions were non-Newtonian liquids exhibiting a yield stress. The flow behaviour could be described well by the Herschel–Bulkley model. The undisrupted network structure of all suspensions could be classified as a weak gel with a rather low critical strain. Particle concentration, size and morphology (surface/shape) turned out to be key structural properties controlling the rheological parameters of these tomato-derived suspensions. Increase in yield stress and storage modulus with particle concentration could be fitted to a power law model. The ratio of static yield stress to dynamic yield stress turned out to be larger for particles with a more irregular, less intact surface, showing the enhanced tendency of the latter particles to build up structure in rest conditions. A unique linear relation was found between the static yield stress and the maximal elastic stress in oscillatory tests, independent of the particle properties. Finally, replacing the serum phase by water led to a substantial decrease in network strength, especially in quiescent conditions.     

Textural properties of agarose gels. I. Rheological and fracture properties

Small- and large-strain rheological methods were used to develop rheological profiles of agarose gels, including linear, non-linear, and fracture properties. Gel properties were examined under conditions of varying agarose concentration (0.5–2.5% w/w), glycerol concentration (0–60% w/w), and strain rate (0.0017–0.17 s⁻¹). Small-strain behaviors were primarily elastic with only slight frequency dependence. Large-strain behaviors and fracture properties were dependent upon strain rate, agarose and glycerol concentration. Increasing concentrations of agarose produced an increasingly stronger, more brittle network, while increasing concentrations of glycerol produced an increasingly stronger, more deformable network. All fracture properties and non-linear behaviors increased with increasing strain rate in a similar manner, suggesting a general mechanism responsible for strain rate effects that is similar for non-linear and fracture behavior. Increasing concentrations of agarose and glycerol, respectively, increased and decreased the strain rate dependence of non-linear behavior. Phenomenological models were evaluated for describing non-linear behavior. A second-order polynomial equation was determined to describe the data more accurately than the commonly used BST equation [Blatz, P. J., Sharda, S. C., & Tschoegl, N. W. (1974). Strain energy function for rubberlike materials based on a generalized measure of strain. Transactions of the Society of Rheology, 18 (1) 145–161.], providing an estimated parameter that allowed relative non-linear behavior to be reliably quantified.     

APPLICATION OF AN IN-LINE RHEOLOGICAL CHARACTERIZATION METHOD TO CHEMICALLY MODIFIED AND NATIVE CORN STARCH

The application of an in‐line ultrasonics‐based rheological characterization method for measuring the rheological properties of 6% (w/v) acid‐thinned and native corn starch suspensions and gels was studied. The measurements were performed in steady, laminar pipe flow using a 5 MHz frequency transducer to determine the radial shear rate distribution. Two pressure transducers were used to measure the pressure drop allowing the shear stress distribution to be calculated through the conservation of linear momentum. It was possible to obtain shear viscosity over a range of shear rates, 1–50 1/s, from a single velocity profile. A comparison of the shear viscosity function at different flow rates showed that this method could be a valid method of process rheometry during the manufacturing of starch‐based products. Both ultrasonics and rotational rheometry results showed that acid‐thinned and native corn starch suspensions exhibited Newtonian behavior before heat treatment and non‐Newtonian behavior after heating. Power law consistency index and flow behavior index of the acid‐thinned corn starch gel at 39°C were 0.60 Pa.s ^0.68 and 0.68, respectively; whereas those of the native corn starch were 5.90 Pa.s ^0.37 and 0.37 at 38C. Their consistency index increased and flow behavior index decreased with cooling and a thermoreversible change in the flow behavior index was observed in the native corn starch after storage.     

Characterization of chitosan–oleic acid composite films

Edible films based on high molecular weight chitosan (CH) and different concentrations of oleic acid (OA) were prepared. Film-forming dispersions (FFD) were characterized in terms of rheological properties, surface tension, particle size distribution and ζ-potential. In order to study the impact of the incorporation of OA into the CH matrix, the water sorption isotherms, water vapour permeability (WVP), mechanical properties, and optical properties of the dry films were evaluated. Results showed that the increase in OA promoted changes in the size and surface charge of the FFD particles, which had an impact on the rheological properties of the FFD. As regards the film properties, the higher the OA content, the lower the WVP and the moisture sorption capacity. In general, the addition of OA into the CH matrix leads to a significant increase in gloss and translucency and a decrease in the tensile strength, elongation at break and elastic modulus of the composite films. The mechanical and optical properties of the films were related with their microstructure, which was observed by SEM.     

Effect of hydrocolloids on the pasting and rheological characteristics of resistant starch (type 4)

The pasting and rheological properties of resistant starch-type 4 (RS4) and hydrocolloid mixtures were characterized at 2 different concentrations (0.1 and 0.5%, w/v). When RS4 was mixed with 2 hydrocolloids (pectin and xanthan gum), there was the overall tendency that both swelling power and solubility of the RS4 suspensions significantly increased. Steady shear measurements showed that the RS4 and hydrocolloid samples exhibited shear-thinning behaviors which could be well characterized by the Power law model. A dramatic increase in the viscosity by xanthan gum was also observed, compared to pectin. In addition, dynamic oscillatory tests indicated that the RS4 and hydrocolloid mixtures exhibited more elastic properties with less frequency dependence, compared to RS4 alone. Also, the viscosities of the RS4 suspensions during pasting increased with increasing concentrations of the hydrocolloids used and these effects became significantly dominant when xanthan gum was incorporated.     

胀果甘草细胞悬浮培养流变特性分析

流变特性是发酵过程的重要数据之一,影响着整个过程的质量、动量和能量的传递。利用旋转黏度计测定甘草细胞悬浮培养液的流变特性及其随发酵周期的变化,结果表明,甘草细胞悬浮液在发酵初期近似于牛顿流体,随着细胞浓度的逐渐增大,悬浮液呈假塑性非牛顿流体特性,稠度系数k增大,流变指数n减小,且各流变学参数之间有一定的函数关系,根据发酵液不同时期的流变特性进行合理控制可以得到更高的发酵效率。     

In situ tensile deformation of zein films with plasticizers and filler materials

Material deformation is a dynamic process. Visualisation of this deformation can help to understand the local deformation and fracture behaviour. Zein (the prolamin protein from maize) films with different amount of plasticizers (0–25%) and different filler materials (maize oil, Dimodan^®, Vestosint^®, at 25% (w/w) to protein) were deformed under tension and observed at micron scale in real time by a confocal laser scanning microscope (CLSM). The addition of plasticizers increased strain and decreased stress of zein films. At low level of plasticizers (6.25% and 12%), zein films deformed and fracture through micro-crack formation and propagation normal the tensile axis. At high Plasticization, only micro-pores were observed during tensile deformation. The filler material oil and Dimodan^® increased, but Vestosint^® decreased tensile strain in comparison to the control. This shows that the fracture dynamic is affected by the filler materials and is indeed observed by the CLSM. Analysis of local strain by Fluospheres^® as particle tracking showed a good linear correlation with the tensile strain of the plasticized zein films. The local strains of filler materials and zein matrix in the films were different from the overall tensile strain. The combination of CLSM with a fluospheres^® as particle tracking is a good method to study local deformation in biomaterials to understand the deformation and fracture behaviour of biomaterials.     

肌肉胶原蛋白特性对嫩度的影响

本试验对不同月龄苏尼特羊不同部位的肌肉胶原蛋白特性进行了分析。其结果表明,随着月龄的增加,总胶原蛋白、可溶性胶原蛋白、不溶性胶原蛋白的含量都呈增加的趋势,而可溶性胶原蛋白的溶解度却在随月龄的增加呈下降的趋势。相关分析表明,肌肉的剪切值与总胶原蛋白、可溶性胶原蛋白为极显著正相关(P<0.01),胶原蛋白溶解度与剪切值成极显著(P<0.01)负相关。这些结果表明,通过测定肌肉胶原蛋白的含量可以较客观的评价肉的嫩度。     

Effect of Tomato Paste on Rheological Properties and Particle Size Distribution of Model Oil-in-Water Emulsions

The role of tomato paste in stabilizing model o/w salad dressing formulations pre-stabilized with xanthan and propylene glycol alginate was studied at levels of tomato paste ranging from 3 to 12% using creep measurements, steady shear measurements and particle size measurements. The addition of tomato paste shifted the particle size distribution to lower values; this distribution was a function of aging time. Creep and steady shear measurements showed an increase in rheological parameters and an increase in viscosity, respectively, suggesting that at higher or equal levels of 6% tomato paste the stability of the o/w emulsion was enhanced significantly.     

Microstructure of highly concentrated tomato suspensions on homogenisation and subsequent shearing

The changes in the microstructure of tomato paste suspensions have been investigated during homogenisation and subsequent shearing in suspensions with similar composition, at three tomato paste concentrations 10, 30 and 40%. The suspensions were characterised by the particle size distribution (PSD), volume fraction (ø), and dynamic rheological properties (G′, G″). All suspensions exhibit a solid-like behaviour with G′ > G″. Micrographs indicate that the process of homogenisation creates a smooth network of finer particles, that is easily disrupted by prolonged shearing, giving rise to the formation of densely packed flocs that become clearly oriented in the direction of the shearing. At high concentrations, these changes in the microstructure on homogenisation and subsequent shearing were better reflected by differences in ø than in G′. The rheological behaviour of the suspensions exhibits a power-law dependence on ø, over a large range of PSD and for 0.05 < ø < 0.55. Finally, an experimental equation, including ø and the size of the coarse particles in the surface-weighted PSD, is found to accurately estimate G′ (R² > 99.3%, p < 0.001).     

RHEOLOGY OF LIQUID FOODS - A REVIEW1

Liquid foods are classified and their properties discussed under various types of rheological behavior: Newtonian, pseudoplastic, shear thickening, thixotropic, and viscoelastic. Rheological data on selected liquid foods are summarized in either tabular form or in the form of equations. Wherever possible the influence of temperature, constituents, and structure on the rheological behavior is detailed. Because many foods are suspensions, the measurement of flow properties of suspensions and factors influencing their rheological behavior are also covered. Finally, the relationship between the flow behavior and the sensory evaluation of mouth feel and viscosity is discussed.     

Separating the Role of Particles and the Suspending Fluid for the Flow of Soy Milks

The paper describes a model and a simple experimental method to determine suspension transport properties, separating the role of particles from the suspending fluid. Shear stresses are described as consisting of 2 components: 1st, a shear stress caused by the flow of the suspending fluid and 2nd, a shear stress caused by direct interaction between suspended particles. We show that the determination of these shear stresses of a complex (food) suspension is largely independent of the definition of its suspending fluid. The rheological behavior of soy milks at low and intermediate moisture contents was studied, and results are compared with those obtained previously. The method evidences that the high viscosity of soy milks is predominantly caused by direct particle interaction.     

Giant squid skin gelatin: Chemical composition and biophysical characterization

Gelatin was extracted from the skin of giant squid (Dosidicus gigas) with a yield of 7.5% on a wet weight basis through a novel cold maturation process and it was chemical, physicochemical and structurally characterized. Squid skin gelatin (SSG) had high protein content (89%) with an amino acid profile similar to that of interstitial collagen. Infrared spectroscopy and circular dichroism confirmed the existence of specific bands of collagen and gelatin which are modified during their thermal transition. Amino acids present in SSG were revealed by NMR signals. Fluorescence spectroscopy revealed emission due to pyridinoline cross-links. Differential scanning calorimetry confirmed that SSG is a weak thermo-reversible gel. Scanning electron microscopy showed porous components within the SSG structure which agree with the viscosity and water holding capacity values obtained. These results led to a better understanding on the molecular structure of SSG which accounts for its well known rheological and physicochemical properties.