The rheological behaviour and microstructural properties of rehydrated cell wall particle (CWP) d... more The rheological behaviour and microstructural properties of rehydrated cell wall particle (CWP) dispersions and CWPexanthan mixtures were investigated using small-deformation rheology and confocal laser scanning microscopy. Dispersions with two different CWP particle sizes were used. CWP dispersions were found to be elastic with a weak-gel type behaviour. The elastic modulus was a function of the CWP concentration c p and depended on the particle size of the CWP. The addition of xanthan to the CWP dispersions was found to affect the rheological behaviour of the CWPexanthan mixtures at low CWP concentration (c p 1 wt%), due to the increase in the viscoelastic properties of the continuous phase. At high CWP concentrations (c p ! 3%), the effect of xanthan on the rheological behaviour of the CWPexanthan mixtures was marginal, as the viscoelastic behaviour of the mixtures was dominated by the CWP particle network, with xanthan molecules entrapped in the interstitial voids. However, at intermediate CWP volume fractions (e.g. at a CWP concentration c p ¼ 2%) both xanthan and CWP phases contributed to the viscoelastic behaviour of the CWPexanthan mixtures.
The rheological behaviour of plant cell-wall particle dispersions was investigated using dynamic ... more The rheological behaviour of plant cell-wall particle dispersions was investigated using dynamic oscillatory measurements. Two starting plant materials, broccoli stem and carrot were used and two types of particles were obtained by mechanically shearing blanched (80 • C, 10 min) or cooked (100 • C, 15 min) plant tissues. Blanching resulted in cell-wall particles made up of a collection of clusters of cells with an average particles size of ∼200 m, while cooking generated nearly all single-cell particles with an average particle size of ∼80 m. The rheological measurements showed that in the range of weight concentrations considered (∼0.5% to ∼8%) the dispersions behaved as elastic materials with the elastic modulus G higher than G within the frequency range (0.01-10 Hz). This study shows that the behaviour of the complex modulus G* as a function of the effective volume fraction can be modelled using different theoretical equations. To do so, it is assumed that below a critical volume fraction c a network of plant cell-wall particles was formed and G* as a function of obeys a power-law relationship. However above c , where the particles were highly packed, G* could be modelled using theoretical equations developed for concentrated emulsions and elastic particle dispersions.
A purified water-soluble fraction (ICP5) of a polysaccharide, isolated from a local Maori mushroo... more A purified water-soluble fraction (ICP5) of a polysaccharide, isolated from a local Maori mushroom Iliodiction cibarium in New Zealand, was investigated for its structural properties. Size exclusion chromatography and dynamic light scattering showed that ICP5 had a large MW of 1.6×10(5) Da with a hydrodynamic diameter of 83±8 nm. Particle size measurements also displayed the tendency of ICP5 to aggregate when suspended in water. The results of GC-MS, FTIR and NMR analyses allowed some characteristics of the chemical structure of ICP5 to be determined. GC-MS results showed that ICP5 contained only glucose (81.61%), galactose (12.90%) and mannose (5.49%) monomers. The characterized fragment structures of ICP5 were found to be dominantly consisting of uronic acids, which formed a backbone containing 1,4-β-d-GlcpA. A small amount of unsaturated uronic acid also appeared to be present.
ABSTRACT The effects of added unmodified amylopectin starch, modified amylopectin starch and amyl... more ABSTRACT The effects of added unmodified amylopectin starch, modified amylopectin starch and amylose starch on the formation and properties of emulsions (4 wt.% corn oil) made with an extensively hydrolysed commercial whey protein (WPH) product under a range of conditions were examined. The rate of coalescence was calculated based on the changes in the droplet size of the emulsions during storage at 20 degrees C. The rates of creaming and coalescence in emulsions containing amylopectin starches were enhanced with increasing concentration of the starches during storage for up to 7 days. At a given starch concentration, the rate of coalescence was higher in the emulsions containing modified amylopectin starch than in those containing unmodified amylopectin starch, whereas it was lowest in the emulsions containing amylose starch. All emulsions containing unmodified and modified amylopectin starches showed flocculation of oil droplets by a depletion mechanism. However, flocculation was not observed in the emulsions containing amylose starch. The extent of flocculation was considered to correlate with the rate of coalescence of oil droplets. The different rates of coalescence could be explained on the basis of the strength of the depletion potential, which was dependent on the molecular weight and the radius of gyration of the starches. At high levels of starch addition (>1.5%), the rate of coalescence decreased gradually, apparently because of the high viscosity of the aqueous phase caused by the starch.
Conventional diffusing-wave spectroscopy (DWS) was combined with a CCD-camera based diffusing-wav... more Conventional diffusing-wave spectroscopy (DWS) was combined with a CCD-camera based diffusing-wave spectroscopy (MSDWS) to study acid induced skim milk gels. This allowed the measurement of intensity autocorrelation functions from 10-6 to 3×103 s, giving access to both fast and slow dynamic modes of these gels.
The effect of heat treatment on reconstituted 10 wt% skim milks containing up to 20 mM added CaCl... more The effect of heat treatment on reconstituted 10 wt% skim milks containing up to 20 mM added CaCl 2 at different pH values (pH 6.0-7.2), was investigated both in situ and after cooling of the heat treated milks. Measurements of pH in situ showed that pH decreased at high temperature, that the decrease in pH increases with the increase in the initial pH and that the magnitude of the decrease in pH was greater for milks with added CaCl 2 . Marked increases in the viscosity at 25 C of heated milks indicated that milks without added CaCl 2 with initial pH 6.2 and milks with 10 mM added CaCl 2 with initial pH 6.4, heated at 90 C were not heat stable. At a given heating temperature, it was possible to superimpose the measured viscosity of samples with or without added CaCl 2 on the same curve when these were plotted as a function of the pH at that temperature instead of the initial milk temperature. To further demonstrate this finding a DWS experimental set-up was built and in situ measurements were performed on the milk samples heated at 75 C for 10 min. The DWS measurements showed that ha, the product of the viscosity with particle size, can also be superimposed for all the measured samples, when plotted as a function of the pH at the heating temperatures. Both the viscosity and DWS data demonstrate the importance of the pH at the heating-temperatures in influencing heat-induced changes in milk.
ABSTRACT Single polysaccharide force spectroscopy has yielded particularly interesting data, the ... more ABSTRACT Single polysaccharide force spectroscopy has yielded particularly interesting data, the interpretation of which requires the marriage of statistical-mechanical theories of polymer physics to the complexities afforded by possible force-induced conformational transitions of the constituent sugar rings. However, the difficulty of designing handles for the specific attachment of the different ends of polysaccharide chains to substrates, such as piezoelectric scanners, cantilevers or microbeads has meant that the majority of studies to date have been carried out with the polymer physisorbed to the substrates between which it is stretched, or at best chemically attached via bonds formed at uncontrolled locations along the length of the molecule. This means that the lengths of obtained polysaccharide stretches, as well as the forces that can be placed on the molecule without generating detachment, are generally smaller than those obtainable for polymers that offer the ability to be covalently attached to substrates specifically at their ends. As a consequence it is troublesome and tedious to record a statistically significant number of force curves that extend chains to high enough forces to investigate certain conformational transitions, such as the boat-to-inverted chair, exhibited by polysaccharides such as pectin. Herein, single molecule force-extension curves have been measured for the several pectin samples using AFM. The results are compared when either (1) the polymers have been physisorbed between the cantilever and the surface of the piezo-electric scanner, under several different solvent conditions of pH and ionic strength, or (2) the polymer molecule has been chemically attached at one end to the piezo surface using a recently reported coupling procedure. In fact, using such a chemical attachment to tether the end of the polysaccharide, reduced the frequency of successful stretching events obtained in a particular location, confirming the role of surface diffusion in the physisorbed experiments. Nevertheless, when polymer stretches were successfully recorded, the force that could be applied before detachment was significantly increased, indicating that this methodology has great potential for improving the acquisition of data reporting on force-induced conformational transitions of the sugar ring that require the application of significant stresses.
The rheological behaviour and microstructural properties of rehydrated cell wall particle (CWP) d... more The rheological behaviour and microstructural properties of rehydrated cell wall particle (CWP) dispersions and CWPexanthan mixtures were investigated using small-deformation rheology and confocal laser scanning microscopy. Dispersions with two different CWP particle sizes were used. CWP dispersions were found to be elastic with a weak-gel type behaviour. The elastic modulus was a function of the CWP concentration c p and depended on the particle size of the CWP. The addition of xanthan to the CWP dispersions was found to affect the rheological behaviour of the CWPexanthan mixtures at low CWP concentration (c p 1 wt%), due to the increase in the viscoelastic properties of the continuous phase. At high CWP concentrations (c p ! 3%), the effect of xanthan on the rheological behaviour of the CWPexanthan mixtures was marginal, as the viscoelastic behaviour of the mixtures was dominated by the CWP particle network, with xanthan molecules entrapped in the interstitial voids. However, at intermediate CWP volume fractions (e.g. at a CWP concentration c p ¼ 2%) both xanthan and CWP phases contributed to the viscoelastic behaviour of the CWPexanthan mixtures.
The rheological behaviour of plant cell-wall particle dispersions was investigated using dynamic ... more The rheological behaviour of plant cell-wall particle dispersions was investigated using dynamic oscillatory measurements. Two starting plant materials, broccoli stem and carrot were used and two types of particles were obtained by mechanically shearing blanched (80 • C, 10 min) or cooked (100 • C, 15 min) plant tissues. Blanching resulted in cell-wall particles made up of a collection of clusters of cells with an average particles size of ∼200 m, while cooking generated nearly all single-cell particles with an average particle size of ∼80 m. The rheological measurements showed that in the range of weight concentrations considered (∼0.5% to ∼8%) the dispersions behaved as elastic materials with the elastic modulus G higher than G within the frequency range (0.01-10 Hz). This study shows that the behaviour of the complex modulus G* as a function of the effective volume fraction can be modelled using different theoretical equations. To do so, it is assumed that below a critical volume fraction c a network of plant cell-wall particles was formed and G* as a function of obeys a power-law relationship. However above c , where the particles were highly packed, G* could be modelled using theoretical equations developed for concentrated emulsions and elastic particle dispersions.
A purified water-soluble fraction (ICP5) of a polysaccharide, isolated from a local Maori mushroo... more A purified water-soluble fraction (ICP5) of a polysaccharide, isolated from a local Maori mushroom Iliodiction cibarium in New Zealand, was investigated for its structural properties. Size exclusion chromatography and dynamic light scattering showed that ICP5 had a large MW of 1.6×10(5) Da with a hydrodynamic diameter of 83±8 nm. Particle size measurements also displayed the tendency of ICP5 to aggregate when suspended in water. The results of GC-MS, FTIR and NMR analyses allowed some characteristics of the chemical structure of ICP5 to be determined. GC-MS results showed that ICP5 contained only glucose (81.61%), galactose (12.90%) and mannose (5.49%) monomers. The characterized fragment structures of ICP5 were found to be dominantly consisting of uronic acids, which formed a backbone containing 1,4-β-d-GlcpA. A small amount of unsaturated uronic acid also appeared to be present.
ABSTRACT The effects of added unmodified amylopectin starch, modified amylopectin starch and amyl... more ABSTRACT The effects of added unmodified amylopectin starch, modified amylopectin starch and amylose starch on the formation and properties of emulsions (4 wt.% corn oil) made with an extensively hydrolysed commercial whey protein (WPH) product under a range of conditions were examined. The rate of coalescence was calculated based on the changes in the droplet size of the emulsions during storage at 20 degrees C. The rates of creaming and coalescence in emulsions containing amylopectin starches were enhanced with increasing concentration of the starches during storage for up to 7 days. At a given starch concentration, the rate of coalescence was higher in the emulsions containing modified amylopectin starch than in those containing unmodified amylopectin starch, whereas it was lowest in the emulsions containing amylose starch. All emulsions containing unmodified and modified amylopectin starches showed flocculation of oil droplets by a depletion mechanism. However, flocculation was not observed in the emulsions containing amylose starch. The extent of flocculation was considered to correlate with the rate of coalescence of oil droplets. The different rates of coalescence could be explained on the basis of the strength of the depletion potential, which was dependent on the molecular weight and the radius of gyration of the starches. At high levels of starch addition (>1.5%), the rate of coalescence decreased gradually, apparently because of the high viscosity of the aqueous phase caused by the starch.
Conventional diffusing-wave spectroscopy (DWS) was combined with a CCD-camera based diffusing-wav... more Conventional diffusing-wave spectroscopy (DWS) was combined with a CCD-camera based diffusing-wave spectroscopy (MSDWS) to study acid induced skim milk gels. This allowed the measurement of intensity autocorrelation functions from 10-6 to 3×103 s, giving access to both fast and slow dynamic modes of these gels.
The effect of heat treatment on reconstituted 10 wt% skim milks containing up to 20 mM added CaCl... more The effect of heat treatment on reconstituted 10 wt% skim milks containing up to 20 mM added CaCl 2 at different pH values (pH 6.0-7.2), was investigated both in situ and after cooling of the heat treated milks. Measurements of pH in situ showed that pH decreased at high temperature, that the decrease in pH increases with the increase in the initial pH and that the magnitude of the decrease in pH was greater for milks with added CaCl 2 . Marked increases in the viscosity at 25 C of heated milks indicated that milks without added CaCl 2 with initial pH 6.2 and milks with 10 mM added CaCl 2 with initial pH 6.4, heated at 90 C were not heat stable. At a given heating temperature, it was possible to superimpose the measured viscosity of samples with or without added CaCl 2 on the same curve when these were plotted as a function of the pH at that temperature instead of the initial milk temperature. To further demonstrate this finding a DWS experimental set-up was built and in situ measurements were performed on the milk samples heated at 75 C for 10 min. The DWS measurements showed that ha, the product of the viscosity with particle size, can also be superimposed for all the measured samples, when plotted as a function of the pH at the heating temperatures. Both the viscosity and DWS data demonstrate the importance of the pH at the heating-temperatures in influencing heat-induced changes in milk.
ABSTRACT Single polysaccharide force spectroscopy has yielded particularly interesting data, the ... more ABSTRACT Single polysaccharide force spectroscopy has yielded particularly interesting data, the interpretation of which requires the marriage of statistical-mechanical theories of polymer physics to the complexities afforded by possible force-induced conformational transitions of the constituent sugar rings. However, the difficulty of designing handles for the specific attachment of the different ends of polysaccharide chains to substrates, such as piezoelectric scanners, cantilevers or microbeads has meant that the majority of studies to date have been carried out with the polymer physisorbed to the substrates between which it is stretched, or at best chemically attached via bonds formed at uncontrolled locations along the length of the molecule. This means that the lengths of obtained polysaccharide stretches, as well as the forces that can be placed on the molecule without generating detachment, are generally smaller than those obtainable for polymers that offer the ability to be covalently attached to substrates specifically at their ends. As a consequence it is troublesome and tedious to record a statistically significant number of force curves that extend chains to high enough forces to investigate certain conformational transitions, such as the boat-to-inverted chair, exhibited by polysaccharides such as pectin. Herein, single molecule force-extension curves have been measured for the several pectin samples using AFM. The results are compared when either (1) the polymers have been physisorbed between the cantilever and the surface of the piezo-electric scanner, under several different solvent conditions of pH and ionic strength, or (2) the polymer molecule has been chemically attached at one end to the piezo surface using a recently reported coupling procedure. In fact, using such a chemical attachment to tether the end of the polysaccharide, reduced the frequency of successful stretching events obtained in a particular location, confirming the role of surface diffusion in the physisorbed experiments. Nevertheless, when polymer stretches were successfully recorded, the force that could be applied before detachment was significantly increased, indicating that this methodology has great potential for improving the acquisition of data reporting on force-induced conformational transitions of the sugar ring that require the application of significant stresses.
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Papers by Yacine Hemar