Centre for Water Soluble Polymers

New starches: Physicochemical properties of sweetsop (Annona squamosa) and soursop (Annona muricata) starches

L M. Nwokocha et al. — Mon, 14 Feb 2011 07:50:39 PST

Starch from the fruits of sweetsop (Anonna squamosa) and soursop (Anonna muricata) were isolated and purified and the fat, ash, phosphorus and protein contents measured. The amount of amylose present was determined spectrophotometrically and found to be very similar ( 19%) for both starches. Scanning electron microscopy showed very small indented and spherical granules from both with an average granule size of 4.84 μm and 4.72 μm, respectively. The physicochemical properties, namely the swelling power, solubility, pasting characteristics, paste clarity and freeze–thaw stability were studied to assess the functionality of the starch pastes as hydrocolloids. The sweetsop starch showed higher swelling power and solubility compared to soursop starch and had a lower gelatinization temperature indicating a weaker granular structure. Sweetsop starch exhibited a lower pasting temperature, higher viscosity peak, higher viscosity breakdown and lower setback, higher paste clarity and freeze–thaw stability compared to soursop starch. The low gelatinization temperature and high freeze thaw stability of sweetsop starch are comparable to that of waxy corn. The properties of sweetsop indicate that it has potential for application as a thickener in frozen foods.

Electrostatic Interaction and Complex Formation between Gum Arabic and Bovine Serum Albumin

T Vinayahan et al. — Thu, 06 Jan 2011 08:15:42 PST

The interaction of gum arabic (GA) and bovine serum albumin (BSA) has been investigated through turbidity and light scattering intensity measurements and by the use of dynamic light scattering, laser Doppler velocimetry, and isothermal titration calorimetry. It has been shown that GA and BSA can form soluble and insoluble complexes depending on the solution pH and the mixing ratio and is a function of the net charge on the complex. Soluble complexes were obtained when the electrophoretic mobility was greater than ±1. 5 μm s−1 V−1 cm−1. Changes in the value of the isoelectric point of the complexes with mixing ratio and isothermal titration calorimetric data indicated that complexes formed at pHs 3 and 4 consisted of 60 BSA molecules for every GA molecule, while at pH 5 there were 10 BSA molecules per GA molecule. Calorimetric studies also indicated that the interaction occurred in two stages at both pH 3 and pH 4, but that the nature of the interaction at these two pH values was significantly different. This was attributed to differences in the relative magnitude of the positive and negative charges on the BSA and GA, respectively, and possibly due to changes in the BSA conformation. The fact that there is an interaction at pH 5, which is above the isoelectric point of the BSA, is due to the interaction of the carboxylate groups on the GA with positive patches on the BSA or to the charge regulation of the protein−polysaccharide system brought about by changes in dissociation equilibria. Complexation is reduced as the ionic strength of the solvent increases and is prevented at a NaCl concentration of 120 mM.

Electrostatic Interaction and Complex Formation between Gum Arabic and Bovine Serum Albumin

T Vinayahan et al. — Tue, 21 Dec 2010 06:34:23 PST

Determination of the calorific value of gum Arabic in rats using modified versions of the growth bioassay and the digestibility assay

Chris J. Smith et al. — Wed, 13 Oct 2010 06:41:36 PDT

Not available

Molecular interactions of plant and algal polysaccharides

Peter A. Williams — Wed, 03 Mar 2010 06:56:46 PST

This paper gives an overview of the interaction in solution of certain plant and algal polysaccharides with cations and also of their interaction in admixture with other polysaccharides and proteins. The mechanism of gelation of pectin and alginate in the presence of calcium ions is discussed together with the specific binding of potassium ions to kappa carrageenan and its influence on the coli-helix transition. The associative and segregative phase behaviour that is encountered in aqueous solutions of mixed polysaccharide systems is considered together with the formation of soluble and insoluble complexes in mixtures of polysaccharides and proteins.

Effect of Polydispersity on Fluorescence Quenching in Micelles Formed by Telechelic Associative Polymers

Rob J. English et al. — Tue, 02 Feb 2010 02:33:12 PST

Time-resolved fluorescence quenching studies, using pyrene as a probe for micellar environments in solutions of a telechelic associating polymer based on PEG with n-C12 (dodecyl) hydrophobic end groups, have been carried out to determine the aggregation number(s) of the micelles. At low [pyrene]/[hydrophobe] values, η, quencher-average aggregation numbers, Nq, calculated from the fitting of the fluorescence decay curves to the Infelta equation were found to decrease rapidly as η increased. By fitting the Nq vs η plots to a cubic curve [Warr, G. G.; Grieser, F. J. Chem. Soc., Faraday Trans. 1 1986, 82, 1813], this observation was shown to be consistent with a highly skewed, polydisperse distribution of micelle aggregation numbers, described by a weight-average aggregation number of 75 and a standard deviation of 86. For a given polymer concentration in the range 1.0−2.5 g dL-1, the fluorescence decay curves did not produce parallel log(I/I0) vs time plots, as would be expected for a monodisperse array of micelles. Instead, the plots showed a characteristic intersection. Simulation of these curves using Infelta-type equations could not reproduce this behavior, indicating that a more refined model may be needed. This detailed study of the distribution of aggregation number in associative telechelic polymers is discussed in the context of recent investigations [Meng, X.-X.; Russel, W. B. Macromolecules 2005, 38, 593], from which it is suggested that polydispersity of micelle size is to be expected as a normal feature of such systems.

Hydrophobically Modified Associative Polymer Solutions: Rheology and Microstructure in the Presence of Nonionic Surfactants

Rob J. English et al. — Tue, 02 Feb 2010 02:15:21 PST

We report on the rheology and morphology of a hydrophobically modified alkali-swellable emulsion (HASE) polymer solubilized in alkaline media containing nonionic surfactants. The HASE polymer consists of complex alkylaryl hydrophobes composed of oligomeric nonylphenol condensates attached to a poly(ethyl acrylate-co-methacrylic acid) backbone. The complex linear viscoelastic response of the polymer in alkaline solution suggests an unentangled network with an appreciable fraction of microgel. The concentration and hydrophile−lipophile balance (HLB) of nonionic surfactants profoundly affect the solution rheology. A surfactant of high HLB inhibits the dynamic network connectivity of the HASE polymer, as demonstrated by reductions of both the steady-shear viscosity and the dynamic storage modulus. The shear-induced structuring previously reported for this polymer is also progressively diminished as the surfactant concentration is increased. In contrast, the addition of a low-HLB surfactant promotes system structuring, as evidenced by (i) increases in the shear viscosity and the high-frequency plateau modulus and (ii) retention of the ability to undergo shear-induced structuring. We also employ cryofracture-replication transmission electron microscopy for the first time with regard to HASE associative polymers to examine the morphological characteristics of selected systems. The morphology of the HASE polymer in both latex and solubilized form appears more complex than previously anticipated, and a reasonable interpretation of these new data is provided.

Interaction of Sodium Dodecyl Sulfate with Methacrylate−PEG Comb Copolymers

H Middleton et al. — Mon, 01 Feb 2010 08:48:53 PST

A series of sodium methacrylate and poly(ethylene glycol) (PEG) comb copolymers (MAA/PEG) with approximate PEG chain lengths of 7, 11, and 22 ethylene oxide units were synthesized by free radical polymerization. Their weight-average molecular mass was found to be 66000. A commercial sample of a PEG comb polymer with an acrylic backbone was also used in the studies (Sokalan HP 80). The interaction of the MAA/PEG comb polymers and pure sodium methacrylate (SPMA) with sodium dodecyl sulfate (SDS) was studied by ESR spectroscopy using 5-doxyl stearic acid (5-DSA) spin probe and by conductivity measurements. Surfactant aggregation in water occurred at SDS concentrations lower than the surfactant critical micelle concentration (cmc) and depended on the polymer concentration. The observations have been attributed to changes in the effective ionic strength of the systems due to the polymer itself, and it has been concluded that there is no interaction between the MAA/PEG comb copolymers or SPMA and SDS. This has been confirmed by the fact that the decrease in surfactant aggregation concentration is similar in magnitude to the decrease observed on adding NaCl when counterion ion condensation effects are taken into account. It is apparent that the electrostatic repulsions between the surfactant molecules and the methacrylate backbone of the MAA/PEG comb copolymers inhibit association of SDS with the PEG side chains.

SANS and Rheology Study of Aqueous Solutions and Gels Containing Highly Swollen Diblock Copolymer Micelles

V Catelletto et al. — Mon, 01 Feb 2010 08:31:57 PST

Aqueous micellar solutions and gels of the diblock copolymer E398B19 (E = oxyethylene, B = oxybutylene) have been investigated by rheology and small-angle neutron scattering (SANS) in the liquid, soft gel, and hard gel phases. Rheology experiments were used to confirm the microstructure and flow behavior of the system in the vicinity of the liquid−soft gel boundary previously located, as well as to identify a new liquid−hard gel transition at low temperatures. The dimensions of the micelles in the liquid phase were obtained from the micellar form factor described by a core/shell model. The parameters extracted from the modeling were in good agreement with previous results for the same system from light scattering. The micellar radius was found to decrease with temperature in the liquid phase, as a consequence of the contraction of the corona chains, caused by a decrease in solvent quality for poly(oxyethylene) at high temperature. The shape of the corona as a whole was preserved on increasing temperature, only undergoing a reduction in width. The equilibrium phase is fluid at volume fractions lower than the volume fraction for freezing of hard spheres, φf = 0.494, in good agreement with a system of hard spheres. In the hard gel, the micelles are arranged in a bcc structure, as expected for micelles with lengthy E blocks.

New Insights into the Mechanism of Gelation of Alginate and Pectin: Charge Annihilation and Reversal Mechanism

C K. Siew et al. — Wed, 20 Jan 2010 06:13:50 PST

Studies have been undertaken on the binding of Mn2+ ions to two alginate samples of different mannuronate:guluronate ratios (M:G), a sample of low-ester amidated pectin and poly(acrylic acid) (PAA). The binding of Ca2+ ions has also been included for the latter for comparison. The binding curves showed an initial steep rise at low additions of Mn2+ or Ca2+ indicating that all of the ions were bound to the polymer chains with none remaining in solution. At higher additions, the binding curves showed a plateau region and the maximum amount bound, θ, was found to be 0.2, 0.2, 0.25, and 0.33 mol M2+/mol COO- for high M:G alginate, low M:G alginate, pectin, and PAA, respectively. The binding curves for Mn2+ and Ca2+ with PAA were superimposable. In all cases, θ was less than the stoichiometric equivalent and also less than predicted by Manning counterion condensation theory. The linear charge density, ξ, for the polymers is 1.49, 1.55, 1.62, and 2.85, and it was found that at maximum binding the effective linear charge density, ξeffective, decreased to a value close to 1 in each case and not 0.5 as predicted from Manning's two-variable theory. The mobility of the PAA chains has been followed by electron spin resonance spectroscopy using nitroxide spin labels covalently attached to the polymer, and the gelation of the pectin and alginate samples has been monitored using small deformation oscillatory experiments. For PAA at maximum binding, it was noted that there was a loss of chain mobility and precipitation. For pectin and alginate, gelation occurred and the stoichiometric ratio for maximum binding corresponded to the stoichiometric ratio for the maximum in G‘. Precipitation and gelation are attributed to the formation of polymer−metal complexes involving one or two carboxylate groups resulting in charge reversal or charge annihilation.

Dilute Polyacrylamide Solutions under Uniaxial Extensional Flow

E Pelletier et al. — Wed, 20 Jan 2010 05:59:07 PST

The shear and extensional viscosities, dynamic viscosities, and normal forces of a series of polyacrylamide solutions of varying molar mass have been determined in a Boger fluid at varying concentrations. The critical strain rate under extensional flow that can be defined from the departure from Newtonian behavior, εc, was found to be independent of the concentration and varied in the same way as the critical coil−stretch strain rate with the molar mass. A quantitative comparison indicated that εc is a decade lower than the strain rate predicted to characterize the coil−stretch transition. This difference indicates that εc reflects the average deformation of the chains over the range of strain rates.

Inhibition of Protein Adsorption onto Silica by Polyvinylpyrrolidone

S Robinson et al. — Wed, 20 Jan 2010 05:45:41 PST

Isotherms for the adsorption of poly(vinylpyrrolidone) (PVP) and bovine serum albumin (BSA) onto silica have been determined. The adsorption capacity for PVP increased with increasing molecular mass but was independent of pH and ionic strength. The adsorbed layer thickness, δ, was determined from ζ potential measurements. δ was found to increase with increasing surface coverage but was significantly less than the polymer radius of gyration even at the adsorption plateau, indicating that the polymer coils flattened at the surface. BSA did not adsorb onto silica from water at pH 7 because of electrostatic repulsions, but adsorption did occur in the presence of electrolyte. The amount of BSA adsorbed at plateau coverage increased from 0.1 mg/m2 in 0.001 M NaCl to 1.0 mg/m2 in 0.5 M NaCl. BSA adsorption was significantly inhibited but not completely prevented, by precoating the silica particles with PVP. Even at low PVP surface coverages, where δ had very low values, some inhibition occurred. Furthermore, PVP was able to desorb most but not all BSA molecules from the silica particles.

Characterization of the Surface-Active Components of Sugar Beet Pectin and the Hydrodynamic Thickness of the Adsorbed Pectin Layer

C K. Siew et al. — Wed, 20 Jan 2010 05:26:13 PST

The fraction of sugar beet pectin (SBP) adsorbed onto limonene oil droplets during emulsification has been isolated, and its chemical and physicochemical characteristics have been determined. While the SBP sample itself was found to contain 2.67 and 1.06% protein and ferulic acid, respectively, the adsorbed fraction contained 11.10% protein and 2.16% ferulic acid. The adsorbed fraction was also found to have a higher degree of acetylation, notably at the C2 position on the galacturonic acid residues, and was also found to contain a higher proportion of neutral sugars, which are present in the ramified side chains of the pectin molecules. The thickness of the layer of SBP adsorbed onto polystyrene latex particles was studied by dynamic light scattering and was found to increase with increasing surface coverage. It was found to have a value of 140 nm at plateau coverage, which closely corresponded to the hydrodynamic diameter of the pectin chains. The adsorbed layer thickness was found to be sensitive to pH and the presence of electrolyte. The thickness at a surface coverage of 20 mg/m2 in the absence of electrolyte at pH 4 was 107 nm and at pH 8.8 was 70 nm, while at pH 4 in the presence of 10 mM NaCl the thickness was found to be 70 nm. It was concluded that the SBP molecules form multilayers at the surface due to electrostatic interaction between the positively charged protein moieties and the galacturonic acid residues. The removal of calcium from the SBP had no effect on the adsorbed layer thickness; hence, multilayer formation due to calcium ion cross-linking was considered unlikely.

Elucidation of the Emulsification Properties of Sugar Beet Pectin

Peter A. Williams et al. — Tue, 19 Jan 2010 08:38:58 PST

A protocol has been developed to fractionate sugar beet pectin using hydrophobic affinity chromatography. Three samples eluted from the column using 4 M NaCl as solvent (fractions 1A, 1B, and 1C), two fractions eluted using 2 M NaCl (fractions 2A and 2B), and one fraction eluted using water (fraction 3). The fractions were shown to be very polydisperse, and differences between the GPC refractive index and UV absorbance (214 nm) elution profiles demonstrated chemical heterogeneity. They were found to contain significantly different proportions of protein (1A, 2.79%; 1B, 0.97%; 1C, 0.77%; 2A, 1.41%; 2B, 5.09%; and 3, 5.89%) and ferulic acid (approximately 1A, 0.5%; 1B, 0.5%; 1C, 0.9%; 2B, 1.5%; and 3, 2%). The weight-average molecular mass, Mw, of the fractions also varied (1A, 153 kDa; 1B, 155 kDa; 1C, 306 kDa; 2A, 562 kDa; 2B, 470 kDa; 3, 282 kDa). Three fractions, that is, 1A, 1B, and 3, produced orange oil emulsions with a relatively small droplet size that were stable over a period of weeks. The other three fractions (1C, 2A, and 2B with higher Mw values) produced emulsions with an initially larger droplet size, and the droplet size increased considerably over time. The increased droplet size may be influenced by the viscosity of the aqueous continuous phase. There was no simple relationship between protein or ferulic acid content and emulsification ability. For example, fraction 1B, which contained the lowest proportion of both protein and ferulic acid, produced stable emulsions of similar droplet size to fraction 3, which contained the largest proportion of protein and ferulic acid. The role of protein in the emulsification process was investigated by measuring the amount of protein in the aqueous phase before and after emulsification. It was clearly demonstrated that proteinaceous material adsorbed at the oil−water interface. It is evident that the emulsification properties of sugar beet pectin are influenced by the accessibility of the protein and ferulic acid groups to the surface of the oil droplets, the proportion of ester groups, and the molecular mass distribution of the fractions.

Adsorption of Gum Arabic, Egg White Protein, and Their Mixtures at the Oil−Water Interface in Limonene Oil-in-Water Emulsions

S R. Padala et al. — Tue, 19 Jan 2010 08:20:18 PST

The adsorption behavior of gum Arabic, egg white protein, and their mixtures at the oil−water interface for 20% limonene oil emulsions has been investigated at pH 3.5 and 7.5. It has been shown that protein-rich fractions of gum Arabic adsorb onto limonene oil droplets and that there is no significant molecular mass dependence. The amount adsorbed was determined from differences in the intensities of the gel permeation chromatography elution profiles of the gum before and after preparing emulsions and was found to be 6.5 and 5 mg/m2 at pH 3.5 and 7.5, respectively. These values are greater than might be expected for monolayer coverage. The amount of protein associated with the gum Arabic adsorbed was about 0.25 mg/m2, which corresponds to 26% of the total protein present in the gum. In comparison, the amount of egg white protein adsorbed was found to be 1.2 and 0.8 mg/m2, respectively, at pH 3.5 and 7.5, which are typical values for monolayer coverage. For gum Arabic−egg white protein mixtures (1:0.05 w/w corresponding to 1:1 on a molar basis) at pH 7.5, both species are negatively charged, and there is no interaction between them. On formation of emulsions, they compete with each other for surface sites, and egg white protein molecules are adsorbed preferentially, although not exclusively. At pH 3.5, the molecules have opposite charge and interact and at this ratio form soluble electrostatic complexes, which are adsorbed at the interface during emulsification. The droplet size of emulsions prepared with gum Arabic was significantly less than for egg white protein over the concentration range studied. Gum Arabic−egg white protein mixtures (1: 0.05 w/w) at pH 3.5 produced emulsions with a droplet size similar to gum Arabic alone, while those prepared at pH 7.5 produced emulsions with a significantly larger droplet size.

A comparative study of some properties of cassava (Manihot esculenta, Crantz) and cocoyam (Colocasia esculenta, Linn) starches

Peter A. Williams et al. — Mon, 02 Nov 2009 06:56:45 PST

Some properties of cassava and cocoyam starches were studied and compared with a view to determining the functional applications in food systems for which they are suitable. The starches were compared in terms of their microscopic, thermal, physicochemical and rheological properties. Microscopy revealed smaller granule sizes of cocoyam starch compared with cassava. The amylose content was higher in cocoyam starch (33.3%) than in cassava starch (29.3%). Gelatinization in cassava starch occurred at a lower temperature range (60.11 o -72.67oC) compared with cocoyam (72.96o – 80.25oC) with the endothermic gelatinization enthalpy higher in cocoyam. The swelling power and solubility patterns indicated lower relaxation temperature, higher swelling and solubilization rates in cassava starch compared with cocoyam starch. The pasting characteristics of 8% (db, dry basis) starch slurry showed that cassava had higher peak viscosity but lower stability and setback ratios compared with cocoyam. This indicates that cocoyam starch paste is better in withstanding processing conditions and would present a superior thickening characteristic than cassava starch paste. The flow properties of both starch pastes showed non-Newtonian behaviour and could be best described by the Herschel-Bulkley model. The rate index and yield stress of cocoyam starch paste was higher than that of cassava. The storage modulus of cocoyam starch paste was higher than that of cassava indicating that cocoyam starch paste was more rigid than cassava starch paste. Cassava starch paste exhibited higher paste clarity and freeze-thaw stability than cocoyam starch paste. The properties of cassava and cocoyam starches dictate their food applications.

Isolation and Rheological Characterization of Mucuna flagellipes Seed Gum

Louis M. Nwokocha et al. — Mon, 02 Nov 2009 06:56:16 PST

The gum from M. flagellipes seed endosperm has been isolated and characterised using capillary viscometry and steady shear and small deformation oscillatory rheometry. The endosperm was found to constitute 67.15% of the whole seed and yielded 32.6% of gum. The Huggins and Kraemer plots obtained by capillary viscometry gave an intrinsic viscosity of 7.9 dL/g and viscosity average molecular mass was calculated to be 2.1 x 106 using the Mark Houwink relationship. The zero shear viscosity was plotted against the coil overlap parameter, C[ç], and the slopes of the lines in the dilute and semi-dilute regions were found to be ~ 1.0 and 4.6 respectively. The curves were fitted to the Tuinier and Martin equations and showed only qualitative agreement. The shear flow viscosity profiles indicated that M. flagellipes gum did not exhibit significant shear thinning at polymer concentrations less than 0.5%, however, at higher concentrations, pronounced shear thinning was observed with the relaxation time (ô) increasing with increase in polymer concentration. The dynamic viscosity profiles showed that at all polymer concentrations examined, a Newtonian plateau was obtained at low frequencies indicating that the loss modulus was the dominant response. Plots of log ç versus log ﻵ and log ç* versus log ù were not superimposible and hence did not obey the Cox-Merz rule.