The North East Wales Institute

Wrexham, United Kingdom

The North East Wales Institute

Wrexham, United Kingdom
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Castellani O.,French National Institute for Agricultural Research | Castellani O.,CONICET | Al-Assaf S.,The North East Wales Institute | Axelos M.,French National Institute for Agricultural Research | And 3 more authors.
Food Hydrocolloids | Year: 2010

The ability to adsorb at n-hexadecane - water interface of natural hydrocolloids was quantified by dynamic drop tensiometry. Conventional and matured hydrocolloids samples from Acacia senegal, Acacia seyal (AcSey), Sugar Beet Pectin (SBP) and natural untreated Gum Ghatti (GG), were studied in aqueous solutions at pH 4.5. Maturation of A. senegal gum (Acacia (sen) SUPERGUM™ EM2, designated as EM2) increased its ability to lower interfacial tension and the elastic characteristics of the interfacial film. This change in properties can be attributed to the increase in molecular weight and in arabino-galactan-protein (AGP) content. EM2 exhibited the best interfacial properties. Conventional and matured AcSey presented interfacial properties that were similar to conventional A. senegal (GAc), correlating with minimal changes observed in their structural features after maturation. Gum ghatti reacted similarly to EM2 and presented relatively fast kinetic profiles, revealing the good qualities of this gum. The kinetics associated with all the hydrocolloids at pH 4.5 have been described using a mathematical model, from which quantitative parameters as onset time or half-time of interfacial-tension-decrease were determined. Compared to the other hydrocolloids, SBP adsorbs by a different mechanism. However, pectin presented the lowest final interfacial tension and gave the more elastic interfacial film. Acidification of hydrocolloid solutions to pH 3.1 increased both the ability to lower the interfacial tension and the elastic characteristics of interfacial film. The effect of structural modifications on interfacial properties was demonstrated, and clarifies further the already observed emulsification behaviour of the studied hydrocolloid. © 2009 Elsevier Ltd. All rights reserved.


Castellani O.,French National Institute for Agricultural Research | Castellani O.,CONICET | Guibert D.,French National Institute for Agricultural Research | Al-Assaf S.,The North East Wales Institute | And 4 more authors.
Food Hydrocolloids | Year: 2010

The emulsifying properties and interfacial behaviour of conventional arabic gum (Acacia Senegal, control gum) and after thermal maturation (EM1 and EM2) were studied. All gums presented good oil in water emulsifying capacities. However, after 20-60 high-pressure homogenization passes, matured gums formed more homogenous emulsions with smaller mean oil droplets (0.4 μm) than the control gum (0.65 μm). Modification of pH from 4.5 to 7.0 did not affect sample characteristics. The film-forming capability of all samples at air-water interface was studied using adsorbed and spread techniques. The greater the amount and molecular mass of the arabinogalactan protein (AGP) component in the gum, the better the interfacial properties (tension drop kinetic and interfacial tension final values). Good dilatational elasticity was found for all three gums samples, corresponding to highly elastic interfacial films. The spread films of matured gum EM2 rearranged during compression, passing through liquid expanded, liquid condensed into solid states. Conversely, control and EM1 gums only formed liquid expanded films and smaller surface coverage than EM2. Analytical interfacial results confirm the improved emulsifying properties of matured gums. The properties of the AGP molecules in the gums could be responsible for these differences. © 2009 Elsevier Ltd. All rights reserved.


Castellani O.,French National Institute for Agricultural Research | Castellani O.,CONICET | Gaillard C.,French National Institute for Agricultural Research | Vie V.,Rennes Institute of Physics | And 5 more authors.
Food Hydrocolloids | Year: 2010

The spreading capacity and surface layer characteristics (morphology and mechanical properties) of different hydrocolloids emulsifiers were compared at air-water interfaces. Acacia senegal, Acacia seyal (AcSey), sugar beet pectin (SBP) in conventional and matured states and two conventional samples of gum Ghatti (GG) were studied in aqueous solutions at pH 4.5 and 3.1. Samples were analysed by their Langmuir compression isotherms. At pH 4.5, the conventional A. senegal (GAc) and A. seyal (AcSeyc) samples exhibited low spreading capacity compared with the other hydrocolloids. The capacity to spread on the surface was improved by the maturation process applied to A. senegal gums and to SBP, but had little effect on the A. seyal samples. The elasticity at zero deformation rate was homogenous for the hydrocolloids. Only A. seyal samples showed high resistance to layer compression, probably due to their low specific volume because of their more compact structure. The matured A. senegal gum was hydrophobically fractionated to separate the main components which were studied individually. The arabinogalactan protein (AGP) component dominates the surface behaviour of this hydrocolloid, and it was confirmed that the arabinogalactan (AG) component did not exhibit surface activity. Acidification of the sub-phase to pH 3.1 improved the spreading and mechanical properties of the layers for all conventional and matured samples, which is in agreement with previous results at n-hexadecane-water interface. However, the GG samples were not affected by pH changes and exhibited similar Langmuir isotherms at both pH values. A. senegal gums were further studied by atomic force microscopy (AFM) and ellipsometry. In aqueous solutions circular particles of about 11 nm in diameter were detected at pH 4.5 for GAc, whereas matured A. senegal gum (designated as EM2) showed circular objects of about 25 nm diameter. Aggregated particles were observed in both samples, but their proportion in EM2 was higher than for GAc. By AFM analysis, the film layer formed by EM2 samples at the air-water interface (pH 4.5) at a surface pressure of 28 mN/m was thick (about 3 times the height of the particles). The roughness and larger particle sizes were more evident for EM2 samples. AFM and ellipsometry at pH 3.1 showed that the surface layer of both samples were thicker and made up of a higher proportion of aggregates. © 2009 Elsevier Ltd. All rights reserved.

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