Browsing by Author "Kontogiorgos, Vassilis"

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    Emulsifying properties of Ghanaian grewia gum
    (International Journal of Food Science and Technology, 2020) Kpodo, Fidelis M.; Agbenorhevi, Jacob K.; Alba, Katerina; Kontogiorgos, Vassilis; 0000-0002-7949-0502; 0000-0002-8516-7656; 0000-0001-7943-3412
    Grewia gums were extracted with phosphate (PB) and sodium metabisulphite buffers (SMB) and their emulsification properties in acidic oil-in-water emulsions on ageing were studied by means of droplet size distribution, f-potential measurements, interfacial composition analysis and viscometry. PB extracts showed smaller droplet sizes (~10 lm) than SMB isolates (>35 lm) and greater long-term stability. PB stabilised emulsions also demonstrated the least polysaccharide (~0.6 mg m 2 ) and protein (~0.2 mg m 2) interfacial coverage compared with SMB counterparts (~1.5 mg m 2 for polysaccharide and ~ 1 mg m 2 for protein). f-Potential measurements revealed negative interfacial charge for all emulsions confirming the presence of polysaccharide-laden interfaces. Droplet size distribution also varied among emulsions during ageing indicating a complex relationship between interfacial composition and stability. The present work shows that different emulsifying properties may be obtained depending on the extraction technique employed that could be exploited in preparation of emulsions for flavour or bioactive-delivery applications.
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    Phase behaviour of oat b-glucan/sodium caseinate mixtures varying in molecular weight
    (Food Chemistry, 2013) Agbenorhevi, Jacob K.; Kontogiorgos, Vassilis; Kasapis, Stefan; 0000-0002-8516-7656; 0000-0001-6016-7580; 0000-0003-2742-931X
    The isothermal phase behaviour at 5 C of mixtures of sodium caseinate and oat b-glucan isolates varying in molecular weight (MW) was investigated by means of phase diagram construction, rheometry, fluorescence microscopy and electrophoresis. Phase diagrams indicated that the compatibility of the b-glucan/sodium caseinate system increases as b-glucan MW decreases. Images of mixtures taken at various biopolymer concentrations revealed phase separated domains. Results also revealed that at the state of thermodynamic equilibrium, lower MW samples yielded considerable viscosity in the mixture. At equivalent hydrodynamic volume of b-glucan in the mixtures, samples varying in molecular weight exhibited similar flow behaviour. A deviation dependent on the protein concentration was observed for the high MW sample in the concentrated regime due to the size of b-glucan aggregates formed. Results demonstrate that by controlling the structural features of b-glucan in mixtures with sodium caseinate, informed manipulation of rheological properties in these systems can be achieved.
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    Rheological and microstructural investigation of oat -glucan isolates varying in molecular weight
    (International Journal of Biological Macromolecules, 2011) Agbenorhevi, Jacob K.; Kontogiorgos, Vassilis; Kirby, Andrew R.; Morris, Victor, J.; Tosh, Susan M.; 0000-0002-8516-7656; 0000-0001-6016-7580
    The rheological properties and microstructure of aqueous oat -glucan solutions varying in molecular weight were investigated. The structural features and molecular weights (MW) were characterized by 13C NMR spectroscopy and high performance size-exclusion chromatography (HPSEC), respectively. The microstructure of the -glucans dispersions was also examined by atomic force microscopy (AFM). The samples with -glucan content between 78 and 86% on a dry weight basis had MW, intrinsic viscosity ([ ]) and critical concentration (c*) in the range of 142–2800 × 103 g/mol, 1.7–7.2 dl/g and 0.25–1.10 g/dl, respectively. The flow and viscoelastic behaviour was highly dependent on MW and on the concentration of the -glucans dispersions. Pseudoplastic behaviour was exhibited at high concentrations and Newtonian behaviour was evident atlow concentrations. At the same concentration,the viscosity was higher for higher MW samples. The Cox–Merz rule was applicable for the lower molecular weight samples at higher concentrations whereas the high molecular weight sample deviated at concentrations greater than 1.0%,w/v. The mechanical spectra with variation of both MW and concentration were typical of entangled biopolymer solutions. AFM images revealed the formation of clusters or aggregates linked via individual polymer chains scattered heterogeneously throughout the system. The aggregate size increased with the molecular weight of the samples investigated and has been linked to the rheological behaviour of the samples.
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    Rheological and microstructural investigation of oat -glucan isolates varying in molecular weight
    (International Journal of Biological Macromolecules, 2011) Agbenorhevi, Jacob K.; Kontogiorgos, Vassilis; Kirby, Andrew R.; Morris, Victor J.; Tosh, Susan M.; 0000-0002-8516-7656
    The rheological properties and microstructure of aqueous oat -glucan solutions varying in molecular weight were investigated. The structural features and molecular weights (MW) were characterized by 13C NMR spectroscopy and high performance size-exclusion chromatography (HPSEC), respectively. The microstructure of the -glucans dispersions was also examined by atomic force microscopy (AFM). The samples with -glucan content between 78 and 86% on a dry weight basis had MW, intrinsic viscosity ([ ]) and critical concentration (c*) in the range of 142–2800 × 103 g/mol, 1.7–7.2 dl/g and 0.25–1.10 g/dl, respectively. The flow and viscoelastic behaviour was highly dependent on MW and on the concentration of the -glucans dispersions. Pseudoplastic behaviour was exhibited at high concentrations and Newtonian behaviour was evident at low concentrations. At the same concentration,the viscosity was higher for higher MW samples. The Cox–Merz rule was applicable for the lower molecular weight samples at higher concentrations whereas the high molecular weight sample deviated at concentrations greater than 1.0%, w/v. The mechanical spectra with variation of both MW and concentration were typical of entangled biopolymer solutions. AFM images revealed the formation of clusters or aggregates linked via individual polymer chains scattered heterogeneously throughout the system. The aggregate size increased with the molecular weight of the samples investigated and has been linked to the rheological behaviour of the samples
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    Structure-Function Relationships in Pectin Emulsification
    (Food Biophysics, 2018) Kpodo, Fidelis M.; Agbenorhevi, Jacob K.; Alba, K.; Oduro, Ibok N.; Morris, G. A.; Kontogiorgos, Vassilis; 0000-0002-7949-0502; 0000-0002-8516-7656; 0000-0003-3731-2684
    The emulsifying characteristics of pectins isolated from six different okra genotypes were investigated and their structurefunction relationships have been evaluated. Emulsion formation and stabilization of acidic oil-in-water emulsions (pH 2.0, φ = 0.1) were studied by means of droplet size distribution, ζ-potential measurements, viscometry, interfacial composition analysis and fluorescence microscopy. Fresh and aged emulsions differed in terms of droplet size distribution, interfacial protein and pectin concentrations (Γ) depending on the molecular properties of pectin that was used. Specifically, pectins with intermediate length of RG-I branching with molar ratio of (Ara + Gal)/Rha between 2 and 3 exhibit the optimum emulsification capacity whereas samples with the molar ratio outside this range do not favour emulsification. Additionally, low amounts of RG-I segments (HG/RG-I > 2) improve long term stability of emulsions as opposed to the samples that contain high amounts of RG-I (HG/RG-I < 2) which lead to long term instability. Protein was not found to be the controlling factor for the stability of the dispersions. The present results show that rational design of pectin should be sought before application as functional ingredient in food and/or pharmaceutical systems.
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    Structure-Function Relationships in Pectin Emulsification
    (Food Biophysics, 2018) Kpodo, Fidelis M.; Agbenorhevi, Jacob K.; Alba, K.; Oduro, Ibok N.; Morris, G. A.; Kontogiorgos, Vassilis; 0000-0002-7949-0502; 0000-0002-8516-7656; 0000-0003-3731-2684; 0000-0001-6016-7580
    The emulsifying characteristics of pectins isolated from six different okra genotypes were investigated and their structure function relationships have been evaluated. Emulsion formation and stabilization of acidic oil-in-water emulsions (pH 2.0,φ = 0.1) were studied by means of droplet size distribution, ζ-potential measurements, viscometry, interfacial composition analysis and fluorescence microscopy. Fresh and aged emulsions differed in terms of droplet size distribution, interfacial protein and pectin concentrations (Γ) depending on the molecular properties of pectin that was used. Specifically, pectins with intermediate length of RG-I branching with molar ratio of (Ara + Gal)/Rha between 2 and 3 exhibit the optimum emulsification capacity whereas samples with the molar ratio outside this range do not favour emulsification. Additionally, low amounts of RG-I segments (HG/RG-I > 2) improve long term stability of emulsions as opposed to the samples that contain high amounts of RG-I (HG/RG-I < 2) which lead to long term instability. Protein was not found to be the controlling factor for the stability of the dispersions. The present results show that rational design of pectin should be sought before application as functional ingredient in food and/or pharmaceutical systems.