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Yao X.,Hubei Engineering University | Zhu X.,Huazhong Agricultural University | Zhu X.,Shihezi University | Pan S.,Huazhong Agricultural University | And 5 more authors.
Food Chemistry | Year: 2012

The inhibitory activities of two polymethoxylated flavone (PMFs) monomers (nobiletin and tangeretin) have been investigated against Pseudomonas fluorescens and Pseudomonas aeruginosa in vitro. The effects on cell morphology, the release of cell constituents, the synthesis of proteins and the activities of key dehydrogenase were examined to elucidate their antibacterial mechanism. The concentration of transaminase and reducing sugar in bacterial solutions increased significantly when treated with nobiletin and tangeretin. Electron microscopy showed that the structure of the bacterial cells was destroyed and accompanied with induced cells plasmolysis. Nobiletin and tangeretin also inhibited the activities of succinate dehydrogenase (SDH) and malate dehydrogenase (MDH), and reduced proteins synthesis in bacterial cells. It is proposed that nobiletin and tangeretin destroyed the permeability of the cell membrane, with release of the cell constituents, leading to metabolic dysfunction, inhibition of protein synthesis, and eventually to cell pyknosis and death. © 2011 Elsevier Ltd. All rights reserved.

Li X.,Glyndwr University | Al-Assaf S.,Glyndwr University | Fang Y.,Glyndwr University | Phillips G.O.,Glyndwr University | Phillips G.O.,Phillips Hydrocolloid Research Ltd.
Carbohydrate Polymers | Year: 2013

Fourteen commercial LM-pectin samples were investigated in this study. The degree of esterification (DE) varied from 9.6% to 42.0% and the degree of amidation (DA) from 0% to 25%. Chemical and structural characteristics were examined using atomic absorption (AA), dilute solution capillary viscometry, GPC-MALLS and dynamic light scattering. The intrinsic calcium was in the range of 47-1388 ppm, the intrinsic viscosity varied from 2.9 to 4.9 (dL/g) and the weight average molecular weight (Mw) from 113 to 290 (kDa). Most of the samples had Huggins constants of ∼0.5. However, for samples having acidic pH, Huggins constant values greater than 1, which can be as an indication of aggregation, were obtained. The high Huggins constant value could be reduced to ∼0.5 by the addition of 3 M urea, indicating that the aggregation was stabilised by hydrogen bonding. Shear flow viscosity revealed three types of rheological behaviour. Type A showed pronounced shear thinning behaviour, which was reduced by the addition of hydrogen bonding breaking agent urea. Type B with intrinsic Ca of 1 mM and pH ∼4 showed two shear thinning regions, with significantly enhanced shear viscosity upon addition of calcium. Type C showed the least aggregation due to its pH ∼4 and low intrinsic Ca, but could be converted to type B upon addition of Ca. The effect of Ca on the rheological behaviour of types B and C was further confirmed by CaCl2 and Ca-chelating agent (EDTA). Temperature affected the molecular conformation of all types and most significantly type A by eliminating the hydrogen bonding. © 2012 Elsevier Ltd.

Li X.,Glyndwr University | Fang Y.,Glyndwr University | Phillips G.O.,Glyndwr University | Phillips G.O.,Phillips Hydrocolloid Research Ltd. | Al-Assaf S.,Glyndwr University
Journal of Agricultural and Food Chemistry | Year: 2013

The study investigates the complexes formed between sodium caseinate (SC) and sugar beet pectin (SBP) and to harness them to stabilize SBP emulsions. We find that both hydrophobic and electrostatic interactions are involved in the complexation. In SC/SBP mixed solution, soluble SC/SBP complexes first form on acidification and then aggregate into insoluble complexes, which disassociate into soluble polymers upon further decreasing pH. The critical pH's for the formation of soluble and insoluble complexes and disappearance of insoluble complexes are designated as pHc, pHφ, and pH d, respectively. These critical pH values define four regions in the phase diagram of complexation, and SC/SBP emulsions were prepared in these regions. The results show that the stability of SBP-stabilized emulsion is greatly improved at low SC/SBP ratios and acidic pH's. This enhancement can be attributed to an increase in the amount of adsorbed SBP as a result of cooperative adsorption to sodium caseinate. Using a low ratio of SC/SBP ensured that all caseinate molecules are completely covered by adsorbed SBP chains, which eliminates possible instability induced by thermal aggregation of caseinate molecules resulting from stress acceleration at elevated temperatures. A mechanistic model for the behavior is proposed. © 2013 American Chemical Society.

Gulrez S.K.H.,Glyndwr University | Al-Assaf S.,Glyndwr University | Fang Y.,Glyndwr University | Phillips G.O.,Glyndwr University | And 3 more authors.
Carbohydrate Polymers | Year: 2012

The structure and conformation of xanthan in aqueous solution following various processing treatments typically encountered in its application were investigated in this study. Treatments such as heating, autoclaving, high pressure homogenisation and irradiation were subjected to the same sample. Parameters such as weight average molecular weight (M w), polydispersity index, root mean square radius of gyration, intrinsic viscosity and Huggins constant were used to monitor the effect of these treatments. Additionally, we have quantified the mass recovery of samples examined by gel permeation chromatography and light scattering to properly account for all fractions present in xanthan solutions. Atomic force microscopy (AFM) images together with height measurements confirmed that xanthan conformation is double helical ordered renatured state (pre-heat treated by the manufacturer) in dilute solution conditions and random coil conformation in very dilute solution. The ordered (renatured) conformation is shown to have partially molten double helix, with more flexibility than the perfectly ordered native double helix. Heat treatment for 2 h at 85 °C reduces the M w of xanthan to half its initial value, and mass recovery measurements indicate that it completely overcomes its associative nature. Thermally treated xanthan solution in the dilute region leads to an order-disorder transition, as determined by contour length per unit mass. Similarly, irradiation of xanthan solution results in an order-disorder transition together with the production of single strand low molecular weight molecules. Autoclaving and high pressure homogenisation treatments cause degradation of xanthan. The results from treated xanthan solutions following high pressure homogenisation and irradiation confirm that xanthan does not reassociate. A revised summary of xanthan conformation in solution together with schematic models following the various treatments are proposed. © 2012 Elsevier Ltd.

Fang Y.,Glyndwr University | Al-Assaf S.,Glyndwr University | Phillips G.O.,Phillips Hydrocolloid Research Ltd. | Nishinari K.,Glyndwr University | Williams P.A.,Glyndwr University
Biomacromolecules | Year: 2010

Electron paramagnetic resonance (EPR) is here used to study the interaction between gum arabic and a fatty acid. The EPR spectra of 5-doxyl stearic acid (5-DSA), a spin-labeled fatty acid analog, displayed increasingly anisotropic line features upon addition of gum arabic, indicating a strong immobilization of the nitroxyl moiety when the fatty acid is bound to gum arabic. To understand the nature of the interaction, EPR measurements were carried out at different pHs and using two fractions of gum arabic separated by hydrophobic interaction chromatography (HIC). 5-DSA bound favorably to the hydrophobic fraction, which contains mainly glycoprotein, and a small amount of high molecular weight arabinogalactan protein (AGP). Binding occurred to a less extent to the hydrophilic fraction, which contains essentially arabinogalactan (AG). Such a hydrophobic binding mechanism is further supported by a sharp drop in the binding when pH is raised above the pKa value of 5-DSA (∼pH 5). This is because the ionization of carboxylic groups would lead to increased polarity and hydrophilicity of the fatty acid. A secondary effect involving the formation of ionic hydrogen bonds between carboxylic groups in fatty acid and lysine residues in gum arabic might also contribute. This is consistent with the reduction in binding ability when the pH was elevated above the pKa value of lysine residue (∼pH 10). The biological significance of these findings is considered. © 2010 American Chemical Society.

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