Food Hydrocolloids

Published by Elsevier
Online ISSN: 0268-005X
Publications
Article
The effect of high pressure homogenization on the improvement of the stability hydroxypropyl cellulose (HPC) and micellar casein was investigated. HPC with two molecular weights (80 and 1150 kDa) and micellar casein were mixed in water to a concentration leading to phase separation (0.45% w/v HPC and 3% w/v casein) and immediately subjected to high pressure homogenization ranging from 0 to 300 MPa, in 100 MPa increments. The various dispersions were evaluated for stability, particle size, turbidity, protein content, and viscosity over a period of two weeks and Scanning Transmission Electron Microscopy (STEM) at the end of the storage period. The stability of casein-HPC complexes was enhanced with the increasing homogenization pressure, especially for the complex containing high molecular weight HPC. The apparent particle size of complexes was reduced from ~200nm to ~130nm when using 300 MPa, corresponding to the sharp decrease of absorbance when compared to the non-homogenized controls. High pressure homogenization reduced the viscosity of HPC-casein complexes regardless of the molecular weight of HPC and STEM imagines revealed aggregates consistent with nano-scale protein polysaccharide interactions.
 
Article
Polymethoxyflavones (PMFs) extracted from citrus peel exhibit potent anti-cancer activity, but are highly hydrophobic molecules with poor solubility in both water and oil at ambient and body temperature, which limits their bioavailability. The possibility of encapsulating PMFs within nanoemulsion-based delivery systems to facilitate their application in nutraceutical and pharmaceutical products was investigated. The influence of oil type (corn oil, MCT, orange oil), emulsifier type (β-lactoglobulin, lyso-lecithin, Tween, and DTAB), and neutral cosolvents (glycerol and ethanol) on the formation and stability of PMF-loaded nanoemulsions was examined. Nanoemulsions (r < 100 nm) could be formed using high pressure homogenization for all emulsifier types, except DTAB. Lipid droplet charge could be altered from highly cationic (DTAB), to near neutral (Tween), to highly anionic (β-lactoglobulin, lyso-lecithin) by varying emulsifier type. PMF crystals formed in all nanoemulsions after preparation, which had a tendency to sediment during storage. The size, morphology, and aggregation of PMF crystals depended on preparation method, emulsifier type, oil type, and cosolvent addition. These results have important implications for the development of delivery systems for bioactive components that have poor oil and water solubility at application temperatures.
 
Article
Nutraceuticals provide health benefits, especially for the prevention and treatment of chronic diseases such as diabetes, obesity, cardiovascular disease and cancer. Their incorporation in food supplements, functional foods and medicinal foods is a major technological challenge due to lower water solubility, instability during processing and storage conditions. Carriers that can effectively overcome these predicaments and protect them during product development, consumption and delivery are in high demand. Toward this end, our research approach is to entrap nutraceuticals in the ordered networks of hydrocolloids. We have examined the effect cations in regulating the encapsulated amounts and release characteristics. Iota-carrageenan and eugenol have been chosen as models of hydrocolloid and nutraceutical, respectively, in the presence of Na and Ca ions. The results suggest that carrageenan maintains its network organization even after encapsulating the eugenol molecules. Increased eugenol amounts are found in the Na carrageenan complex compared to the Ca complex, and the release rate is faster from the former but it is more controlled from the latter. These differences highlight the vital role of cations on the encapsulation efficiency and release profiles of hydrocolloid-based nutraceutical carriers. The outcome offers an elegant opportunity for developing novel and value-added food systems employing low-in-cost, nontoxic and heavily consumed food grade hydrocolloids.
 
Article
A particulate form of xanthan gum was prepared by extrusion cooking. The temperature dependence of the viscosity of this form shows similarities to starch with an increase in viscosity to a maximum with increasing temperature as a result of the swelling of the particles. The rheology and mixing behaviour with water of the particulate and conventional molecular forms of xanthan were compared with a modified starch. The particulate xanthan products mixed rapidly with water in a similar way to ungelatinised starch, whereas conventional molecular xanthan systems mixed poorly. Using an experienced sensory panel, model tomato products thickened with the three systems were compared at equal shear viscosities. The panel could not discriminate between the tomato flavour of the three products, but found that the xanthan products were perceived as being significantly thicker. These observations were consistent with previous work. Salt perception for both xanthan products was poorer than for the starch thickened systems. A hypothesis to explain why xanthan does not fit into the previously postulated link between mixing and perception is presented.
 
Article
The influence of high pressure (HP) treatment (200–600 MPa) on the emulsifying activity index (EAI) and emulsifying stability index (ESI) on the 7S and 11S globulins and soya protein isolate (SPI) at pHs 7.5 and 6.5, at different concentrations (0.25–0.75%) was studied. Solubility and surface hydrophobicity were used as indices of the degree of denaturation caused by HP. 7S showed the highest EAI and surface hydrophobicity after treatment at 400 MPa, whereas 11S showed its highest EAI and surface hydrophobicity after treatment at 200 MPa. No significant correlation (P>0.05) was found between solubility and EAI or hydrophobicity. SPI showed the optimum value of EAI after treatment at 400 MPa although its surface hydrophobicity was low. It is suggested that pressure at 400 MPa dissociated the 7S of the SPI into partially or totally denatured monomers that enhanced the surface activity but at the same time, the unfolding of the polypeptides of the 11S within the hexamer led to aggregation, negatively affecting the surface hydrophobicity of the SPI. The ESI values for the non-treated samples of SPI, 7S and 11S were higher at lower concentrations. At the same pH and concentration, the ESI decreased with increasing HP, except for the 7S at pH 7.5 and a protein concentration of 0.75%.
 
Article
The influence of dextran on the interfacial pressure of adsorbing layers of legumin (11S globulin vicia faba) at the planar n-decane/aqueous solution interface was studied under conditions of thermodynamic compatibility and incompatibility between these biopolymers. The thermodynamic incompatibility of legumin with dextran in the bulk aqueous solution leads to an increase in the interfacial pressure of the adsorbing layers of legumin. This effect may be caused by the excluded volume effect between molecules of the biopolymers in the bulk aqueous solution. Opposite effects are observed under conditions of thermodynamic compatibility between these biopolymers. In the latter case they may be related to the intensification of thermodynamically favourable interactions of legumin with dextran molecules in the bulk aqueous solution.
 
Article
The influence of ι-carrageenan (ι-CAR) on the solution, interfacial and emulsifying properties of 11S globulin Viciafaba at low ionic strength and pH 8 has been investigated before and after high-pressure processing at 200 MPa for 20 min. The total calorimetric enthalpy (ΔH) and size exclusion chromatography studies for the pure 11S indicate that there is subunit dissociation and extensive aggregation of the protein during or following treatment. Under the same treatment conditions, 1-anilinonaphthalene-8-sulphonate (ANS) data has shown increased protein surface hydrophobicity. Pressure treatment of 11S gives much lower values of the surface tension, and apparent surface shear rheology experiments show that the molecules in the film adsorbed from the pressurised 11S are much more strongly interacting than those adsorbed from the native 11S. However, emulsions prepared with pressure processed 11S give substantially bigger droplets than those made with the untreated pure protein. Addition of ι-CAR to 11S reduces the denaturation temperature (Tm), the ΔH value, and protein surface hydrophobicity. Size exclusion chromatography at low ionic strength is indicative of complex formation. Tension measurements at the air–water interface are also consistent with the presence of a complex. Emulsions made with the simple 1:0.33 mixture of 11S+ι-CAR give emulsions with smaller droplets and pressure processing of the biopolymer mixture leads to emulsions with even smaller droplets. The presence of ι-CAR at low ionic strength appears to protect the globulin against pressure-induced aggregation.
 
Article
Fourier transform infrared (FTIR) method was used to study the secondary structures of 7S and 11S globulins from soybean proteins using aqueous buffer and reverse micelles extraction method for the first time. The Fourier second derivative was applied to all spectra, revealing that the amideband of 7S and 11S globulins with two extraction methods consisted of eight bands. The I band frequencies were assigned to α-helix, β-sheet, unordered and turn structure. The second derivative spectra of 7S and 11S globulins had been shifted with reverse micellar extraction method compared with their spectra with aqueous buffer extraction method. The relative amount of different structure of 7S and 11S globulins could be estimated through accurate measurement of the band intensities. The results indicated that the percentage of 7S globulin α-helix and β-sheet, turn structures decreased with the reverse micelles extraction (7S globulin: 14.5% α-helix, 45.6% β-sheet, 14.4% unordered, 23.8% turn; 11S globulin: 17.0% α-helix, 47.3% β-sheet, 16.5% unordered, 19.3% turn), compared with 7S (16.5% α-helix, 47.6% β-sheet, 35.9% turn) and 11S (17.0% α-helix, 47.3% β-sheet, 35.8% turn) globulins by the aqueous buffer extraction, while the percentage of 11S globulin α-helix and β-sheet structures did not change. The percentage of unordered structure was 14.4 and 16.5, respectively. The amount change of these substructures might affect functional properties of 7S and 11S globulins.
 
Article
The effect of pH on the thermodynamic properties of the mixed solution of the two different globular proteins, oligomeric globular protein-11S globulin andmonomeric globular protein-ovalbumin, has been studied. Thermodynamic incompatibility of the proteins was observed at pH 7.0 and 7.8, which are above the proteins' isoelectric points. Thermodynamic properties of the system were studied by phase analysis from moderate to high concentration and by light scattering on dilute solutions below the separation threshold. The rise of the concentration region of the protein immiscibility in the mixed protein solution was observed under a pH change from pH 7.8 to 7.0. Comparison of the alteration of the character of the interactions between all components of the solution with pH variation shows that the basic reason for the rise in protein immiscibility with pH decrease (from 7.8 to 7.0) is intensification of the self-association of the mixed proteins, mainly of 11S globulin. It was established that the forces of electrostatic repulsion between both the similar and different protein molecules play a key role in the phase separation of the mixed protein solutions at pH 7.8. In contrast, the results obtained exhibit the determining role of the attractive forces acting between protein molecules and dictating features of the phase state of the mixed protein solution at pH 7.0.
 
Article
The influence of heat (up to 80°C for 2 min) and high-pressure (up to 250 MPa for 20 min) on the emulsifying properties of 11S globulin Vicia faba at pH 8.0 has been investigated for systems containing the sulphated polysaccharides ι-carrageenan (ι-CAR) and κ-carrageenan (κ-CAR). The emulsions (0.5 wt% 11S, 20 vol% n-tetradecane) made with heated or high-pressure treated 11S were found to give substantially larger droplets than those made with the native protein. Visual creaming behaviour has been monitored as a function of storage time. There was a consistent trend of decreasing emulsifying efficiency and emulsion stability with increase in treatment temperature or pressure. Addition of ι-CAR or κ-CAR (3:3–7:1 by weight) to the native protein at low ionic strength led to smaller droplets whose size decreased with increase in polysaccharide concentration and extent of high-pressure treatment (up to 200 MPa). Thermally treated biopolymer mixtures gave emulsions with droplets that did not significantly change with increase in temperature. In all cases, the presence of ι-CAR led to a significant improvement in creaming stability. However, the presence of κ-CAR in untreated and thermally treated (<75°C) mixtures gave rapid serum separation probably due to depletion flocculation. Of the two polysaccharides studied, ι-CAR gave the smallest droplets in fresh emulsions and the best stability with respect to visual creaming behaviour. The observations for 11S alone can be interpreted in terms of pressure or thermally induced unfolding of the protein, which results in a decrease in emulsion efficiency due to dissociation of subunits or protein aggregation. It appears that the strength of interaction of 11S with ι- or κ-CAR is dependent on the charge density on the polysaccharide. The presence of interacting polysaccharide in the heated and high-pressure processed samples seems to inhibit the formation of aggregates. High-pressure treatment of the mixed biopolymer solutions in the presence of sodium chloride (>0.01 M) destabilises the emulsion, and so the protective effect of polysaccharide is lost.
 
Article
This paper presents a study of the effect of aroma compound (hexyl acetate, HxAc) on thermodynamic properties of legumin (11S globulin from broad beans) in an aqueous medium (protein conformational stability and protein–protein interactions) by a combination of gas–liquid chromatography, differential scanning microcalorimetry, static light scattering and sedimentation velocity analysis. The aqueous phase at the ionic strength of 0.05 mol dm−3 was buffered at pH 7.2 and 3.0. The conformational stability of the native 11S globulin (pH 7.2) was maximum at the point of saturation of the protein molecules with the aroma ligand, which was determined from the binding isotherm. At pH 3.0, the protein conformational stability did not change over the same concentration range of HxAc, i.e. where the protein binding capacity for HxAc was studied. As a result of the binding of HxAc with 11S globulin the thermodynamic affinity between protein molecules in an aqueous medium increased in the case of the native protein, remained unchanged for the acid-denatured protein and reduced in the case of the heat-denatured protein at the same concentration of HxAc in the system. An excess of concentration of HxAc in the solutions above the saturation level for the protein, according to the binding isotherm, led to protein aggregation in an aqueous medium owing to spontaneous protein unfolding.
 
Article
Oil-in-water emulsions containing 30% soya oil and various concentrations of sodium caseinate were prepared in a two-stage valve homogenizer. The emulsions were sealed in glass bottles and then heated at 121°C for 15 min in an autoclave. In some experiments, the caseinate solutions were heated at 121°C for 15 min first, mixed with soya oil (to give 30% oil in the final emulsion) and then homogenized. Heat treatment (121°C for 15 min) of either sodium caseinate emulsions or sodium caseinate solutions prior to emulsion formation, at all caseinate concentrations used, resulted in an increase in surface coverage, an increase in creaming stability and a change in the proportions of individual caseins at the droplet surface. Heat treatment of sodium caseinate solutions resulted in the formation of several new peptides, due to protein degradation, as well as polymerization of casein molecules, as revealed by SDS–PAGE. Both the polymerized caseinate material and degradation products were adsorbed efficiently during emulsification; the degradation products were more readily adsorbed than the parent protein. Experiments on heated emulsions indicated that the adsorbed caseinate molecules were more susceptible to degradation during heating than those in solution.
 
Article
The crystalline microstructure and polymorphism of C-type starch from Chinese yam were evaluated by scanning electron microscope (SEM), 13C cross-polarization magic-angle spinning NMR (13C CP/MAS NMR) and powder X-ray diffraction (XRD) technique and acid hydrolysis method. Morphological changes during acid hydrolysis showed that the amorphous or the less crystalline areas were essentially located at the center part of C-type starch granules whereas the semi-crystalline and amorphous growth rings were found mainly in the outer part of the granules. 13C CP/MAS NMR and XRD results revealed that B-type allomorph was hydrolyzed more rapidly than A-type one. The amorphous or less crystalline areas were predominantly composed of B-allomorph whereas the outer semi-crystalline and amorphous growth rings were mostly composed of A-type allomorph. The A- and B-type allomorph coexisted in the individual C-type starch granule. B-type allomorph basically existed at the center part of the granules which was surrounded by the A-type allomorph in the peripheral part of granules.
 
Article
A screening was made among 18 novel strains of Xanthomonas campestris pv pruni. Yields, viscosity and chromatographic patterns of the biopolymers synthesized in a conventional medium (PM II), were analyzed. Yields varied from 2.3 to 8.3 g l−1. Viscosities of 3% (w/v) aqueous solutions at 25, 45 and 65°C, were determined at 6, 12, 30 and 60 rpm. All biopolymers had pseudoplastic behavior. The biopolymers showed three distinct viscosity patterns when temperature increased: no variation, decrease and increase. Polymers that maintained or increased their viscosity had higher mannose concentrations. Strain 06 was chosen for further studies because it showed a higher viscosity at 6 rpm, 26,000 mPa s at 25°C and 27,000 mPa s at 65°C, and a yield of 4.0 g l−1. The influence of the concentration of biopolymer (1 and 2%) and temperature (25, 45 and 65°C) in the viscosity was also determined. A small increase in viscosity when the temperature was raised was observed at both concentrations. Finally, the influence of fermentation time (24–96 h) on yield, viscosity and chemical composition of the biopolymers, was determined. The biopolymer obtained after 24 h of fermentation showed the higher viscosity, but the highest yield was obtained at 72 h. The biopolymer produced by strain 06 after 48 h of incubation showed similar viscosity and rheological behavior to commercial xanthan.
 
Article
The emulsification properties of an isolate of β-lactoglobulin (β-LGI) and a whey protein fraction (WPF) of reconstituted skim milk were studied in a milk-based environment containing anhydrous milk fat at 4 and 18% by modifying protein concentration. At a similar protein-to-fat ratio, fat content per se was not associated with changes in initial particle size, but was related to stability during storage. In the more concentrated emulsions, creaming was inhibited and no longer affected time-dependent aggregation of fat globules, except under the most extreme conditions (i.e. in the presence of a higher proportion of α-lactalbumin, at high initial particle size and at high storage temperature). However, aggregation was enhanced by the presence of a higher proportion of α-lactalbumin, which was detrimental to physical stability.Using laser desorption mass spectroscopy, the molecular mass of a significant proportion of WPFs whey protein was observed to be increased, possibly as a result of lactolation. In addition, β-LGI contained some calcium, which slightly increased the concentration of calcium in emulsions made with β-LGI. These differences in molecular mass and calcium concentration did not enhance the stability of emulsions prepared with β-LGI over that of those prepared with WPF.
 
Article
The structure of a water soluble arabinogalactan isolated from gum ghatti (Gatifolia SD) was elucidated by methylation analysis and 2D NMR spectroscopy. The arabinogalactan fraction (F80) was obtained by a sequential ethanol precipitation of gum ghatti (Gatifolia SD). Methylation and GC–MS analysis indicated that F80 was a highly branched polysaccharide; the terminal sugar residues were about 40.8% of the total sugars. The majority of the terminal units were α-l-Araf, with small amounts of T-GlcpA, T-Arap, T-Rhap and T-Galp. About 14.2% of the total sugar residues were →6)-β-d-Galp-(1→ branched at 3rd and 4th positions. The linear portion of the arabinogalactan was composed of →4)-GlcpA(1→, →6)-Galp(1→ and →2)-l-Araf-(1→ linkages. Based on the results from methylation analysis, 1D (1H, 13C) and 2D (COSY, TOCSY, HMQC and HMBC) NMR spectroscopy, the structure of F80 was proposed as follows:R is one of the following groups: →3)-β-d-Galp-(1→, →5)-β-d-Araf-(1→, →2,3-Manp1→, T-α-l-Araf 1→, T-GlcpA1→ and T-l-Arap 1→. Galactose has the -β-D configuration, while the arabinose and rhamnose are in the α-l form.Graphical abstract
 
Article
The gelling properties of pectins are known not only to be closely related to the degree of esterification (DE), but also to the distribution of the ester groups. In this study we have examined an experimentally designed series of pectins originating from the same mother pectin and deesterified using combinations of two different enzymatic mechanisms. The DE and distribution patterns of methyl ester groups have been analyzed using high-resolution (HR) 1H nuclear magnetic resonance (NMR) spectroscopy on pectin solutions. Quantitative calibration models using partial least squares (PLS) regression were developed with the ability to predict DE as well as the specific enzyme treatment, expressed as amount of ester groups removed with random and block enzyme, respectively. NMR spectroscopy was able to distinguish between enzyme treatments in simple classification by principal component analysis (PCA). This was due to the spatial structure of pectin together with the methyl ester distribution. Nuclear Overhauser effect spectroscopy (NOESY) experiments confirmed all the general assignments with the expected nuclear Overhauser effect (NOE) correlations. Degree of random deesterification (R) was better predicted than the degree of block deesterification (B). The calibration models for prediction of R obtained on extended inverted signal correction (EISC) processed data gave a root mean square error (RMSE) of cross-validation (CV) of 2%p with 4 PLS components (latent variables, LV) and a correlation coefficient (r) of 0.98. Spectral variable selection using interval PLS (iPLS) was shown to be valuable, as all the calibration models were improved.
 
Article
It was demonstrated that macroscopic structural changes of polysaccharide chains, such as random coil–helix transition and aggregation of helices, accompanied with the sol–gel and the gel–sol transition can be monitored by numerically analyzing the temperature dependence of the observed water proton spin–spin relaxation time (T2obs) modified by the chemical exchange between water proton and labile proton on the chain. According to the numerical analysis of T2obs, typical profiles of T2obs against the temperature were simulated with various parameters of the relaxation time (T2i) and the mean residence time (τi) of water and the labile protons on the random coil and the ordered chain as well as the activation energy (Ei,Eex,i) for the motion and the chemical exchange of the respective proton. The difference of structural change of kappa- , iota- , and lambda-carrageenan aqueous systems in the cooling and the heating process was analyzed. In conclusion, (1) the characteristic profile of the temperature dependence of T2obs, commonly observed in the temperature-induced gelling process, is attributable to the variation of fraction of the ordered chain and the relative rate of chemical exchange to the relaxation rate of labile protons on polysaccharide (1/T2p); (2) the loose aggregated or associated structure is detected for iota-carrageenan system; and (3) the thermally stable junction zones formed by well aggregated helices of kappa-carrageenan in the gel state provokes a thermal hysteresis in the temperature-induced structural change (experimentally, in T2obs). It is clarified by the numerical simulation that the aggregated helices formed during further cooling down to the temperature below Tsg results in the T2obs shifts to a longer value in the heating process as compared with that in the cooling process.
 
Article
23Na NMR molecular mobility studies were performed to investigate the interaction between sodium ions and various hydrocolloid—water systems as affected by the nature of the hydrocolloid (ionic and non-ionic) and the concentration of added NaCl (0–5000 mg/100 ml). At low amounts of added NaCl (20–100 mg/100 ml) the transverse relaxation rates (R2) for the ionic gums, kappa-carrageenan and xanthan, rapidly decreased and were larger than those for the non-ionic gums, guar and locust bean. At higher concentrations of added NaCl (>100 mg/100 ml), R2 for the ionic gums gradually levelled off, approaching the R2 values for the non-ionic gums. For the xanthan-water system, the R2 for the endogenous Na+ concentration and very low added NaCl concentrations (<15 mg/100 ml) were also measured. This research suggests that gum type, NaCl and endogenous cation concentrations affect the binding of Na+ to the gums.
 
Article
Gelatinization behavior of starch in an aqueous system was studied in the presence or absence of various guar gum samples with different molecular weights in order to clarify the difference in functions of each guar to starch. Some native corn starches with different amylose/amylopectin ratios were used to clarify which fraction of starch the gums act on. Weight-average molecular weight Mw of the guar samples ranged from 4.7×105 to 34.6×105 g/mol, whereas z-average root-mean-square radius of gyration Rg ranged between 82 and 233 nm from static light-scattering technique. Relationship between Mw and Rg was expressed by the Flory exponent of 0.503. Also, intrinsic viscosity [η] of the guar samples in aqueous solution was in good agreement with Mw determined, and relationship between Mw and [η] was expressed by the Mark–Houwink–Sakurada exponent of 0.517. Gelatinization behavior of starch/guar system was investigated from its viscosity profiles. Guars with Mw values higher than 12.2×105 g/mol shifted the onset of viscosity increase for the system to lower temperatures and increased its peak viscosity upon heating at a relatively low starch concentration (e.g. 5 w/v%). The earlier onset of viscosity increase was independent of Mw of guar, while the increase in peak viscosity was dependent on its Mw. These guars shifted the onset of viscosity increase for the system upward, on the contrary, at a relatively high starch concentration (e.g. 15%). Interaction between guar and starch components, amylose and amylopectin, was hypothesized as one of the factors to govern the gelatinization behavior of starch.
 
Article
Retrogradation behavior of corn starch in an aqueous system was studied in the presence or absence of various guar gum samples with different molecular weights. Dynamic mechanical loss tangent for starch system with 26% amylose (5 w/v%) was increased by the addition of guar (0.5%) after storage at 4 °C for 24 h, which indicated the reduction of gelled fraction in the system, leading to the retardation of short-term retrogradation of starch. This rheological change of the system related to the amount of amylose leached out the starch granules during gelatinization. The higher the molecular weight of guar, the lower the amount of amylose leached, but this effect of guar became less dependent on its molecular weight at above 15.0×105 g/mol. The rate constant determined from the relationship between storage time (for 14 days at 4 °C) and creep compliance for the starch system (15% starch) was decreased in the presence of guar (0.5%), suggesting the retardation of long-term retrogradation of starch. This effect of guar became marked at above 30.0×105 g/mol, which was apparently higher than the critical molecular weight value determined from short-term retrogradation. Syneresis for the starch system (5% starch) was increased adversely by the addition of guar (0.5%) with relatively low molecular weight values (e.g. <5.0×105 g/mol) after storage at 4 °C for 14 days, suggesting the promotion of long-term retrogradation. Functions of guar on the retrogradation behavior of starch were hypothesized considering interactions between guar and starch components; amylose and amylopectin.
 
Article
Generalized 2D correlation spectroscopy (COS) has been applied to FTIR spectra of porcine plasma proteins to elucidate the sequence of events leading to pH- and/or thermal-induced protein unfolding and aggregation. Changes in the amide I′ region of the infrared spectra (in the pH range between 7.5 and 4.5, at 0.5 pH intervals) at 30 °C were especially evident as the pH approached the pI of serum albumin (4.8), with the globulin fraction in the plasma proteins undergoing denaturation prior to serum albumin. The effect of increasing temperature (from 30 to 90 °C, in increments of 5 °C) on the secondary structure of the plasma proteins at pHs in the range of 7.5–6.0 revealed that a decrease in alpha-helical structures is taken place previously to diminish native beta-sheets. So, the overall results of this study demonstrate that serum albumin and the globulin fraction differ in their sensitivity to pH and temperature.
 
Article
Deuterium-labelled (methyl-d3) pectin was prepared by esterifying a lemon peel pectin with methanol-d4. A pure powder sample and multicomponent model confectioneries containing the labelled pectin and various amounts of water were studied by solid-state 2H NMR spectroscopy. In the pure sample the broad 2H NMR lineshape indicates that the only fast motion occurring on the NMR timescale is reorientation of the methyl-d3 group about its C3 axis. In contrast, in systems of 50% water content the 2H NMR lineshape is much narrower, indicating significant motional averaging. As the percentage water in the confectionery systems is reduced to <40% the main effect is the appearance of a broad component in the spectrum associated with a more static motional environment. As the water content decreases further the proportion of labelled pectin in this region increases and the amplitude of the motions decreases, until for systems of <10% water content motions are now slow on the NMR timescale, except for the methyl-d3 group reorientation about its C3 axis, and 2H NMR lineshapes are identical to those observed in the pure powder sample. The evolution of the two component lineshape indicates that the removal of successive amounts of water does not simply ‘stiffen’ the entire system but rather initially restricts motion in certain regions and eventually ‘crystallizes’ distinct domains within the sample.
 
Article
Oat and barley β-glucans were isolated from their respective concentrates that were prepared through a novel technology, containing total phosphorus at 0.920 and 0.170%, w/w, respectively. The highest purity of oat and barley β-glucans achieved was 97 and 90%, w/w (db), respectively. Purified oat and barley β-glucans contained 21.8 and 54.1%, w/w, respectively, of the total phosphorus present in the corresponding β-glucan concentrates. On a weight basis, the total phosphorus content in purified oat and barley β-glucans was 0.201 (degree of substitution (DS)=0.011) and 0.092% (DS=0.005), respectively. 31P NMR of both types of β-glucans showed the presence of inner C-6 carbon bound phosphomonoesters and an unknown form of phosphorus, possibly phospholipids and/or phosphoproteins. In addition to these phosphorus forms, barley β-glucan sample contained pyrophosphate for which the origin was unknown. Although a substantial amount of phytate phosphorus (0.745 and 0.103%, w/w, for oat and barley, respectively) was present in both types of β-glucan concentrates, this form of phosphorus was absent in the purified β-glucan as evidenced by 31P NMR data. Aqueous extractability of oat β-glucan from purified sample at 37 °C was 6.6-fold higher than that of barley β-glucan at the same temperature. This may partly be attributed to the presence of more (46%) negatively charged phosphorus substitution in oat β-glucan than in barley.
 
Article
The heat denaturation and aggregation behaviour of β-lactoglobulin (β-LG) enriched WPI was investigated at pH 4.0 and 7.0 in the presence of arginine HCl, NaCl and GdnHCl using differential scanning calorimetry (DSC) and dynamic light scattering (DLS). Beside the classical endothermic signal attributed to protein heat denaturation, DSC thermograms displayed appearance of an additional exothermic peak in the presence of cosolute. Using in situ DLS, it was shown that the appearance of the exothermic peaks is linked to protein aggregation, in particular to a strong increase in aggregate size. Upon increased cosolute concentration at pH 4.0 the exothermic peak occurred at temperatures lower than the actual denaturation peak (∼85 °C). At this pH, negatively charged chloride anions interact with β-LG leading to charge screening and physical aggregation. At pH 7.0, exothermic peaks appeared at higher temperatures than the denaturation peak (∼75 °C). Upon increased cosolute concentration the exothermic peak was shifted to lower temperatures, indicating protein destabilisation in the presence of cosolutes. Charge screening of β-LG by the positively charged cations (arginine, Na and guanidinium) reduced repulsion forces and promoted aggregation.
 
Article
The influence of protein aggregates on complex coacervation between β-lactoglobulin (β-lg) and acacia gum (AG) has been studied at pH 4.2 using phase diagrams, electrophoretic mobility measurements, laser light scattering and phase contrast optical microscopy. Removal of protein aggregates by centrifugation (pH 4.75, 1 h, 10,000g) led to an aggregate-free β-lg dispersion (AF-BLG) exhibiting a narrow polydispersity in molecular masses (Mw∼18,500 and 64,500) and hydrodynamic radii as determined by GPC and QELS measurements, respectively. Phase diagram determination for the AF-BLG system revealed a two-phase region located in the water-reach corner. In addition, the highest total biopolymer concentration leading to phase separation (4.5 wt%) and the tie-lines shape typically accounted for complex coacervation. The position and extend of the two-phase region differed from that obtained using BLG dispersions (containing protein aggregates). This was partly due to the lowest Mw and Rh polydispersity of the AF-BLG, but also to the decrease of the electrophoretic mobility (μE) of the AF-BLG induced by the protein aggregates elimination (loss of cations in the dispersion). The variation of the μE of the AF-BLG/AG complexes with pH was similar to that of the BLG/AG ones, but of lower intensity due to the decrease of cations in the system. The size distribution of the BLG/AG complexes obtained at pH 4.2 was mainly governed by the presence of large-sized aggregates (10–50 μm). By contrast, AF-BLG/AG coacervates exhibited a volume average diameter (d43) that reached 220 μm for the 2:1 Pr:Ps ratio at pH 4.2, revealing less stability of particles in the system. These results were in agreement with phase contrast optical microscopy that revealed marked differences in the structure of BLG/AG complexes and microparticles as compared to that of AF-BLG/AG coacervates.
 
The effect of temperature on the equilibrium constant for b-lactoglobulin denaturation. Graph were drawn from the 1st-order (A) or 2ndorder (B) Van't Hoff plots (see text for detail).
Thermal stability curves for b-lactoglobulin. Graphs show the effect of temperature on the Gibbs free energy change for stabilisation. Protein concentration was 0.4 mg/ml (dotted lines), 4.0 mg/ml (thin±continuous lines). Average results are shown as continuous line.
Article
The thermal stability of β-lactoglobulin (β-Lg) dimer was reassessed based on a three-state denaturation process involving dissociation and unfolding (dimer⇌monomer⇌unfolded state). The stabilisation Gibbs free energy change for β-Lg dissociation unfolding (ΔGDCUO) was 57.6 kJ mol−1 compared with an estimated 14 kJ mol−1 with β-Lg monomer as the reference native state. The standard enthalpy (ΔHO) and entropy (Delta;SO) change for heat denaturing β-Lg dimer are reported. The new stability parameters are discussed in terms of protein stability function relations.
 
Article
In this study, the amount, size, calcium sensibility, and composition of heat-induced protein particles in the mixture of beta-conglycinin (7S) and whey soybean protein (WSP) dispersion are compared with those of 7S and WSP dispersion to investigate the interactions between WSP and 7S during heating. The addition of 7S prevents WSP from forming large protein particles which can be precipitated by centrifugation at 10,000g for 10 min. The protein in the heated mixture of 7S and WSP (7S/WSP = 1/1) coagulates at higher calcium concentrations than that in the mixture of heated 7S and heated WSP at a ratio of 1/1. This result strongly indicates that 7S and WSP interact with each other during heating and form complex protein particles which have special surface properties that are different from individual 7S and WSP protein particles. Particle size distribution analysis has also shown that 7S prevents WSP from forming larger protein particles during heating. SDS-PAGE analysis shows that lipoxygenase (LOX), beta-amylase, and lectin of WSP and the beta subunit of 7S tend to form a particulate fraction, while the KTI, alpha, and alpha′ subunits tend to form a soluble fraction. WSP, 7S, and their mixture have been heated at 60, 65, 70, 75, 80, 85, 90, and 95 °C for 10 min, and ultracentrifugation analysis shows that about 77–85% of the protein particles were formed at 65–75 °C in all three dispersions. SDS-PAGE analysis indicates that LOX and β-amylase have been denatured and that they have participated in the formation of protein particles when heated within 65–75 °C, while lectin has begun to participate in particle formation at above 85 °C. It is concluded that WSP plays an evident role in the formation of protein particles in soymilk during heating.
 
Article
Association properties of β-lactoglobulin AB (β-Lg) fractionated by gel permeation chromatography (GPC) was studied using dynamic light scattering (DLS) at a concentration of 5% w/v and pH 7.0 from 25 to 70°C. β-Lg fraction with a molecular weight of 18.4 kDa by GPC (monomeric) showed self-association at 25°C. At 25°C ~58% of the protein had an apparent mean diameter <10 nm and the rest between 10 and 100 nm. On heating to 35°C all the protein existed as monomers and dimers. With further heating association increased; large particles with an apparent size of 100–599 nm were seen >45°C indicating that some degree of denaturation occurs even at 45°C. The amount of aggregate <10 nm in size decreased sharply >65°C. Data indicate that β-Lg that was monomeric during GPC, where a linear velocity gradient may exist, was associated even at 25°C under quiescent conditions of the DLS experiments. Association increased progressively with temperature and denaturation, as observed by the formation of large aggregation, starting at 45°C.
 
Article
Gelatinization and retrogradation behaviors of the aqueous starch/iota-carrageenan composite system (0.5 w/v% starch and 0.2% carrageenan) were investigated. Purified iota-carrageenan in sodium form was mixed with corn starch in the presence or absence of various salts. Functions of iota-carrageenan on starch depended on salts added. During gelatinization, the addition of iota-carrageenan lowered the incipient swelling temperature of the composite system with decreased peak viscosity in the absence of added salts and in the presence of monovalent cations, while the temperature increased in the presence of divalent cations. It also increased the rate constant for short-term (<24 h) retrogradation of the composite system with depressed gel-like characters in the presence or absence of salts. The effect of iota-carrageenan to increase the rate constant was the greatest in the absence of added salts and was greater in the presence of monovalent cations than divalent cations. The effect of the polysaccharide to depress gel-like characters was the greatest in the presence of LiCl and NaCl. The molecular mechanism was deduced from microscopy to explain these rheological behaviors mainly from the structural similarity between iota-carrageenan and amylose. Thermodynamic incompatibility between these two substances may explain the early onset of viscosity increase during gelatinization (i.e., upon heating) and the acceleration of subsequent short-term retrogradation due to increased effective concentration of starch or amylose, whereas physical interactions (both molecular complexes and steric hindrance) between the substances may explain the retardation of structural ordering during retrogradation (i.e., upon cooling) due to inhibited amylose aggregation.
 
Article
Influence of microscopic molecular structure imaged using atomic force microscopy (AFM) on macroscopic rheological behavior of carrageenan was investigated in an aqueous system. Two types of carrageenan (iota and kappa) with equivalent average molecular weights, purified by alcohol precipitation and subsequently transformed to the sodium type, were subjected to the investigations at concentrations to form molecular assemblies; gel precursors or microgels (local networks and aggregates) in the presence or absence of cations.AFM observations elucidated the difference in the effect of cations on the (super-) molecular structure of carrageenan. In the case of iota, the addition of K+ increased the stiffness of the strands (composed of helices) and aligned them to a definite direction with some degree of branching, whereas that of Ca2+ mediated the associations between the strands into network-like structures (both of which might be an artifact during drying in preparing the AFM specimens). Each structural change involved, however, no or very low level of side-by-side aggregation between helices, which was in good agreement with rheological data, showing no hysteresis between sol-to-gel and gel-to-sol transitions. In the case of kappa, on the contrary, the addition of K+ or Ca2+ formed localized network through side-by-side aggregation between helices (more apparent with an addition of K+), which was consistent with the thermal hysteresis between sol-to-gel and gel-to-sol transitions, but this interhelical aggregation was not necessarily a prerequisite for gelation. The structure-function relationship and cation selectivity for each carrageenan were discussed.
 
Article
Gum acacia, a natural hydrocolloid, is extensively used as an emulsifier/stabilizer in beverage emulsions. Factors that may affect emulsion formation, emulsion stability and viscosity of the emulsion concentrate were studied to assess their significance, including proximal composition of the gum (protein content and mineral content), gum processing prior to emulsion preparation (pasteurization and demineralization), and pH of the dilute emulsion. Protein content was not related to emulsion stability, whereas minerals decreased stability presumably due to an electrostatic screening effect. Both pasteurization and demineralization favored stability, most likely by promoting protein unfolding and eliminating the screening effect, respectively. Emulsions were less stable at pH=2.5 than at higher pH levels (4.5 and 5.5). There was a significant difference between the two gum species studied (Senegal and Seyal) in their sensitivity to these treatments. The viscosity of the emulsion concentrate was decreased by pasteurization and increased by demineralization. Protein load at the O/W interface and thickness of the adsorbed layer of emulsifier were not related to emulsion stability. The most important colloidal interactions in dilute beverage emulsions are van der Waals, electrostatic and polymeric steric.
 
Article
The compatibility of β-lactoglobulin (β-lg) and acacia gum in aqueous medium was investigated as a function of the pH (3.6–5.0), the protein to polysaccharide weight ratio (50:1–1:20) and the total biopolymer concentration (0.1–5 wt%). The ternary phase diagrams obtained at low ionic strengths (0.005–10.7 mM) typically accounted for phase separation through complex coacervation. Thus a drop-shaped two-phase region was anchored in the water-rich corner. The electrostatic nature of the interactions between the two biopolymers was pointed out according to the pH dependence of the two-phase region's breadth. Following the absorbance of the mixtures at 650 nm, the influence of the protein to polysaccharide ratio was also demonstrated. Electrophoretic mobility (μE) measurements and chemical analyses of separated phases revealed the formation of soluble and insoluble coacervates and complexes. A remarkable value of the protein to polysaccharide weight ratio (2:1) at pH 4.2 gave the same protein to polysaccharide (Pr:Ps) ratio in the two phases after 2 days, implying that electrostatic interactions are maximum between β-lg and acacia gum. The increase of the total biopolymer concentration reduced the influence of pH and protein to polysaccharide ratio. Also, the increase of the pH close to the β-lg IEP reduced the influence of the total biopolymer concentration and Pr:Ps ratio. As the biopolymer content was increased at pH 3.6 and 4.2, the relative β-lg solubility increased probably because of the self-suppression of complex coacervation.
 
Article
The gum fractions isolated from Acacia senegal gum using hydrophobic affinity chromatography have been further characterized by 1H- and 13C-NMR spectroscopy and by methylation analysis. Fractions 1 and 2 are essentially polysaccharides of similar sugar and uronic acid content, the units of which have now been found to be linked in the same manner, despite a difference in the proportion of associated protein (0.44 and 9.18% respectively). The glycoprotein fraction 3 (carbohydrate content 50–54%), comprising a minor but important part of the whole gum, is made up of monosaccharide units in the same relative proportions, which are linked in a similar manner to those found for the major, carbohydrate-rich components. A molecular model proposed earlier, wherein five carbohydrate blocks such as make up fraction 1 are joined to polypeptide to form fraction 2, gains support from the near identity of the carbohydrate moieties in these fractions. The carbohydrate in fraction 3 is of lower molecular weight than that of 1, and may be attached to any of the hydroxy-amino acids present in abundance.
 
Article
Principal component analysis, cluster analysis and discriminant component analysis have been used to study the relationship between the two series of Acacia gums Gummiferae Benth (= subgen Acacia Vas.) and Vulgares Benth (= subgen Aculeiferum Vas.). The main commercial gums within these series A.senegal and A.seyal were scrutinized individually and the Acacia gums, in turn compared with another chemically related, but not species related, Combretum gums. On the basis of %N and composition of 18 amino acids A.seyal falls within the A.senegal cluster. Combretum gums are quite distinctive from the Acacia gums. Analysis by covariance further confirms that despite the lower %N in A.seyal compared to A.senegal this alone is insufficient to distinguish between them based on amino acid composition. On this basis A.seyal and A.senegal are ‘closely related’. When nine analytical parameters associated with the carbohydrate moiety are evaluated, members of the Gummiferae series are found to form a greatly extended cluster in keeping with their wider taxonomic origin and development. Although the Vulgares series members fall into a more compact cluster, there are individual members at the regions of overlap between the two Series more ‘closely related’ to members of the Gummiferae series than to A.senegal, which like A.seyal fall into a compact cluster. Therefore, despite their taxonomic identification as separate species, there are chemical and corporate similarities between A.senegal and A.seyal which signal caution in selecting specific parameters to distinguish between them when setting up a regulatory specification. The results indicate that overall there are greater similarities between A.senegal and A.seyal than there are differences between them.
 
Article
Analytical data for the sugar and amino acid compositions are presented for the gum exudates from Acacia gerrardii Benth. var. gerrardii and Acacia goetzii Harms subsp. goetzii Brenan, which have not been studied previously. Conversion factors have been calculated from the amino acid data to facilitate the conversion of Kjeldahl nitrogen values to protein contents; the factors are considerably higher than that assumed in earlier studies of Acacia spp. The analytical data substantiate previous chemotaxonomic conclusions that species in Bentham's sub-series Gummiferae (e.g. A. gerrardii) all have positive optical rotations, low viscosity, arabinose/galactose ratios greater than unity and low rhamnose contents. In contrast, species in Bentham's subseries Vulgares (e.g. A. goetzii) have negative optical rotations, are comparatively more acidic and more viscous, with arabinose/galactose ratios less than unity and higher proportions of rhamnose; such species can be regarded as being related to A. senegal, the source of commercial gum arabic. The data confirm previous evidence that hydroxyproline and serine are the major amino acids in the proteinaceous components of Acacia gums; such components are structurally and functionally important. Comment is made on the liabilities faced by gum importers.
 
Article
The structure of acacia gum molecules was determined using size exclusion chromatography coupled to multi-angle laser light scattering, refractometry and viscosimetry. Results revealed the presence of many molecular species, including large aggregates, the arabino-galactan protein fraction (AraGP), the arabino-galactan fraction (AraG) and the glyco-protein fraction (GP). The Mw of the two major fractions AraGP and AraG were 2.3 106 and 2.7 105 g mol−1, respectively. The [η], Rg and Rh of the acacia gum sample were 0.23 dl g−1, 14.2 and 11.9 nm, respectively. From the determination of Rg/Rh ratio (1.2) or the exponent ν (0.55) of the power-law relationship between Rg and Mw, it was tentatively suggested that acacia gum molecules displayed a random coil shape.
 
Article
The term “dietary fibre” has been used for more than 30 years. The present concept has evolved from the original physiological–botanical description as being the remnants of plant components that are resistant to hydrolysis by human alimentary enzymes, which were soon extended to include all indigestible plant polysaccharides. Chemical materials such as resistant starch, oligosaccharides, lignin and associated plant substances, which are both soluble and insoluble are now included. Whilst there is widespread understanding in the scientific and medical community, about the material definition, physiological function and health properties of dietary fibre, the food regulators continued to be unable to agree upon a universally accepted international definition. The Codex Alimentarius draft definition, now out to Member States for consultation is discussed and using gum arabic as a case study the paper considers whether this exudate gum, which is approved presently as a food additive (E414 and INS414), conforms to the requirements of the Codex definition.The European Commission (EC) too is working in a vacuum on this subject and has suggested using the EC Novel Foods Regulation EC 258/97 if the product has not been established before May 15, 1997 when this legislation was first introduced. Meanwhile, food manufacturers, use the term “dietary fibre” to describe their products but have no internationally accepted legal definition or approval system to support their practice. It is concluded that gum arabic; like other food fibre materials, is universally recognised scientifically as a food additive but its regulatory status remains a matter of discussion and some uncertainty. The same uncertainty would relate also to the regulatory status, as dietary fibre, of other soluble and insoluble plant/algae polysaccharides.
 
Article
In this study, the gum arabic was used as Acacia senegal. Chemical and physical changes induced by treatment with ionizing radiation were investigated, and doses up to 100 kGy were employed. In the solid state, no significant changes in physical properties of gum arabic could be observed, although there was a small decrease in molecular weight. In aqueous solution at low concentration, gum arabic was mainly degraded, but a small amount of polymerization could also be detected. However, in highly concentrated aqueous solutions, polymerization occurred with minimal degradation.This novel polymerization of gum arabic occurred without the need for any additives and only by using high solute concentrations. Such polymerized gum arabic could be useful as a component in food, cosmetic, agricultural, and hygienic materials. Irradiation at high solute concentrations would provide favourable conditions for the radiation-induced radicals to combine, and so produce step-wise the polymerized gum arabic. These reactive species could result from both direct radiation action and abstraction by water radiolysis products. Gum arabic in aqueous solution at low concentrations, on the other hand, would mainly lead to carbohydrate-free radicals as a result of OH-radical abstraction, which would degrade further, rather than have the opportunity to re-combine.
 
Article
The chemical and physicochemical characteristics of eight authenticated Acacia senegal gum samples from trees of varying age growing in Sudan have been investigated. The samples originated from the Kordofan region in west Sudan which is the traditional source of the gum and from the new plantations established in the El Daley region in east Sudan. The monosaccharide compositions, protein and amino acid contents and optical rotation were found to be similar to values reported in the literature and there were no obvious trends observed with age or source of the tree. The molecular mass distribution was determined by gel permeation chromatography (GPC) using four different detection systems, namely, UV absorbance, refractive index, photon correlation spectroscopy (PCS) and multiangle laser light scattering (MALLS). The weight average molecular masses obtained by GPC agreed well with the values calculated from the intrinsic viscosity and varied for the individual samples between 2×105 and 7.9×105. The highest values were obtained for samples from trees 15 years old. All samples were found to be polydisperse (Mw/Mn=1.3–1.8) and the GPC UV elution profiles demonstrated the existence of three principal molecular mass components with molecular masses of 1-4×106, 1.5–3.0×105 and 1.8×105. The radii of gyration, Rg, and hydrodynamic radii, Rh, obtained by GPC/MALLS and GPC/PCS of all of the molecular species were found to be small relative to their molecular mass. The plot of log Rg against log molecular mass for each sample was linear with a slope of ∼0.42 and the ratio of Rg/Rh was consistently about 0.8+/−0.2 nm. These findings were taken as evidence of a highly branched globular structure consistent with the ‘wattle blossom’ model proposed for arabinogalactan protein complexes generally.
 
Article
An investigation of the molecular structure of Acacia seyal relative to Acacia senegal provides an indication of the components which influence emulsification effectiveness. Samples of A. seyal var. seyal and A. seyal var. fistula were fractionated using gel permeation chromatography. The fractions and the whole gum were analysed to determine the molecular weight, sugar content, amino acid, protein content, nitrogen, and intrinsic viscosity. The results confirm earlier findings that samples of A. seyal, as a broad grouping, have weight average molecular weights several times greater than A. senegal, due to the greater proportion of the high molecular weight component. Although the molecular weight of A. seyal is considerably greater than A. senegal, the intrinsic viscosity is less. The structure is, therefore, more compact, than the structure of A. senegal. The sugar composition and amino acids in each of the gums are identical but are present in different proportions, which is the main reason why A. seyal is dextrorotatory and A. senegal is laevorotatory.
 
Article
The Acacia gum (Acacia senegal var. senegal), which is a food additive approved by Codex Alimentarius, is defined within the Acacia subgenus (family Leguminosae). The structural characteristics associated with a “poor” and “good” emulsifying A. senegal var. senegal exudate gum are identified and it is shown that it is possible to maturate the “poor” emulsifier in a process comparable to that which occurs to the exudate gum as the age of the tree increases from 1 to 15 years and when the gum is stored naturally after collection. Thus, the molecular parameters of the “good” gum can be matched, and the emulsification effectiveness can attain the level of the “good” emulsifier.The process can be further continued to produce a series of gums of precisely structured molecular dimensions with improved properties and if the maturation is continued can yield a hydrogel form of Acacia. The new forms of A. senegal which are described here, and which have not previously been available are designated Acacia (sen) SUPER GUM™ which are constant in properties and with precisely structured molecular dimensions, unlike the naturally occurring gum. The viscosity can be increased up to 20 times compared to the starting material. The controlling factor is the agglomeration of the proteinaceous components within the molecularly disperse system that is A. senegal gum to increase the amount of arabinogalactan protein (AGP) emulsifying component up to more than double the amount present originally. This results in a dramatic increase in the interfacial surface properties and coverage of the oil droplet in oil in water emulsion. No other chemical change is initiated by the maturation process.
 
Article
Acacia gum is a ubiquitous water-soluble material that has been analyzed using a variety of techniques. The absence of a high-resolution technique for the separation of the components of the gum has been an impediment to its characterization. Two complementary electrophoretic methods for the separation and detection of the polysaccharides, glycoproteins, and proteins that constitute Acacia gum and other gums have been developed. The first uses sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) with 2-[N-Morpholino] ethanesulfonic acid (MES) buffer and silver staining for the analysis of the proteins in Acacia gum. Over 10 proteinaceous bands were observed in the M.W. range of 2×103–2×105. The second uses agarose electrophoresis with Tris-Borate (TB) buffer and dansyl hydrazine staining for the analysis of the polysaccharides and glycoproteins in Acacia gum. One to two carbohydrate-containing bands were observed in the high M.W. (<5×106) region. The advantages of electrophoresis over gel filtration chromatography for gum analysis are discussed.
 
Article
Chemometric methods have been used to characterise and evaluate commercial gum arabic in relation to authenticated Acacia senegal specimens and gums from the Combretum series. Principal component (PCA) and discriminant component analysis (DCA) were undertaken using firstly parameters mainly associated with the carbohydrate moiety: specific optical rotation, viscosity, %N. and sugar compositions, galactose, arabinose, rhamnose, equivalent weight, glucuronic acid and 4-methylglucuronic acid. Secondly, the compositions of the 18 amino acids were utilised, and subsequently the 27 features were combined. Of the 54 samples investigated, it is evident that the commercial gum arabic and authenticated Acacia senegal mainly fall into a discrete cluster. The outliers are few and can be explained. The Acacia gums can readily be distinguished from the Combretum gums. The samples are drawn from various countries: Sudan, Niger, Nigeria, Uganda, Oman, Mauritania, Mali, Senegal, Ethiopia, Kenya and Uganda. No significant difference is found in the gum from the main producing countries. Local variants from Oman and Kenya do not conform to the specification. Using PCA with amino acid compositions, the family of gums from Uganda can be distinguished. The gums are drawn from periods ranging from 1903 to the present, and no significant change has taken place in the gum over this period. Neither climate nor nature of the soil introduces any particular difference. When all 27 parameters are used, it can be demonstrated that the amino acids are dominant in establishing the distinctive character of Acacia senegal. Using loading—loading plots, the major distinctive features can be selected. As a result a characterisation is now possible using only four features: rotation, viscosity, lysine and hydroxy-proline compositions. Based only on the two features (specific optical rotation and % N) proposed by the Joint Expert Committee for Food Additives (JECFA), no correlation is possible. It is proposed that such a chemometric classification could be used to set the specification for commercial gum arabic and provide the basis for a practical quality control system for producers and users.
 
Article
This study evaluated the cardiovascular and renal effects of dietary fibre supplementation with Acacia(sen) SUPERGUM™ (gum arabic) in normal individuals and a group of diabetic nephropaths. The normal diet was supplemented with 25 g of SUPERGUM™ daily for a period of 8–12 weeks.For the whole cohort dietary supplementation with SUPERGUM™ resulted in a fall in mean systolic blood pressure [SBP] (138.4 ± 18.9 mmHg to 132.83 ± 15.9 mmHg p = 0.01). Of note was a significant fall in SBP seen in normal individuals who neither had hypertension nor diabetes (129.1 ± 8.3 mmHg vs 123.6 ± 11.5 mmHg, n = 10 p = 0.02).Parameters of arterial stiffness were examined in patients with diabetic nephropathy and a fall in MAP. In this subgroup there was a significant fall in both central systolic and diastolic blood pressures, with no alterations in AI, AI @75 or PWV. This suggests that the beneficial effects of SUPERGUM™ on blood pressure are not the result of alterations in arterial stiffness.There were no effects of SUPERGUM™ on renal function and haemodynamics in patients with diabetic nephropathy. In contrast a reversible change in GFR (113.0 ml min vs 99.4 ml/min, p = 0.02) and ERPF (489.7 ml/min vs 463.0 ml/min, p = 0.04) was shown in the population of healthy volunteers.The key finding of this study is the a significant beneficial effect of dietary supplementation with SUPERGUM™ on blood pressure which is seen in both a patient group with diabetes and mild renal involvement as well as in a normal healthy normotensive cohort.
 
Article
Principal component projection, discriminant component projection and, for classification, linear discriminant analysis (LDA) have been used to study the relationship between and distinguish closely related Acacia, Combretum and Proposis gum exudates, all arabinogalactan proteins. A set of eight gums from the Acacia and seven from Combretum series, selected randomly, could be all correctly classified using LDA. Combretum gums can readily be distinguished from Acacia gums (Vulgares and Gummiferae series) using either analytical parameters associated with either the carbohydrate or protein moieties. The Proposis gums form a closely identifiable grouping, apart from P. Juliflora, which is indistinguishable from Acacia senegal. Gums of the Phyllodinaea series can readily be discriminated from other Acacia species used in the food industry. The method offers a basis for a quality control system to ensure the compliance of commercial gum products with national and international legislative requirements.
 
Article
Models for sterilized, concentrated infant formulae were prepared from whey protein concentrate (WPC) and high-heat non-fat dry milk (NFDM) to yield a casein to whey ratio of 40:60%. The protein, carrageenan and lecithin levels were varied within a number of 2 × 3 factorial designs. Statistical techniques were used to evaluate the relationship of compositional factors to physical stability and to determine which emulsion stability test best predicted stability toward creaming after prolonged storage. Emulsion stability was assessed by gravitational and centrifugal creaming, relative viscosity, adsorbed protein and light scattering. Centrifugation and relative viscosity were the best predictors of 10 and 18-week stability, whereas emulsion activity index and particle size were poor predictors of stability in the infant formula model.
 
Article
Production of cellulose by Acetobacter aceti AJ12368 was optimized in a two-stage fermentation process. A cell growth stage in an air-lift fermenter (agitated culture) was followed by a cellulose formation stage in production incubators (static culture). The optimal moment of process change was at day 3 of agitated culture when the cell density and intracellular Adenosin triphosphate content peaked; at this time culture broth in the air-lift fermenter could be subdivided to feed four production incubators equipped with nine trays. Surface aeration was effective in producing food-use gelatinous cellulose which is homogeneous and low in syneresis. This process was more economical than the conventional fermentation procedure in the Nata industry.
 
Article
Cellulose production by a strain of Acetobacter xylinum (the nata organism) was affected by the type and concentration of sugar, nitrogen source and pH. Fructose, fructose + sucrose, fructose + lactose and sucrose gave the highest yields (5.25–7.38 g/l). Glucose gave low yields when used alone or in combination with other sugars. The pH of all glucose-containing media decreased from pH 5.0 to ~3.0. When fructose alone or in combination with sucrose was used at 1, 5 or 15% concentrations, 5 and 15% total sugar concentrations gave the highest, and similar yields. Organic sources of nitrogen were the most favorable for cellulose biosynthesis. Among the organic sources tested, yeast extract in combination with peptone gave the best product yield. Higher yields of cellulose were obtained at pH 4.5 than at 5.5 and its production was completely inhibited at pH 3.5.
 
Article
The optimum fermentation conditions for the batch, non-agitated production of cellulose by a strain of Acetobacter xylinum was determined by means of response surface methodology. A five-level, four-factor central composite design was used to determine the relationship of four factors (fructose and sucrose concentrations, pH and temperature of incubation) to the response, cellulose yield (in g of crude cellulose/l of medium). All four factors affected cellulose yield significantly. Maximum product yield could be obtained by employing the following predicted optimum fermentation conditions: fructose concentration = 24.8 g/l, sucrose concentration = 76.5 g/l, pH = 4.49 and temperature of incubation = 29.3°C. Upon verification, the predicted cellulose yield (13.24 g/l) was found to be very close to the average experimental yield (12.67 g/l), indicating that the mathematical model obtained was an adequate predictor of cellulose yield. Better yields were obtained in this study than had been obtained by others.
 
Top-cited authors
David Julian Mcclements
  • University of Massachusetts Amherst
Glyn O. Phillips
  • Glyndwr University
Katsuyoshi Nishinari
  • Hubei University of Technology
P. Montero
  • Spanish National Research Council
M. C. Gomez-Guillen
  • Spanish National Research Council