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The Surface Chemistry of Wheat Gluten I. Surface Pressure Measurements

Tschoegl, N. W. and Alexander, A. E. (1960) The Surface Chemistry of Wheat Gluten I. Surface Pressure Measurements. Journal of Colloid Science, 15 (2). pp. 155-167. ISSN 0095-8522.

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Wheat gluten dispersed in a 0.1 M solution of hydrogen chloride in anhydrous chloroethanol was spread at the A/W and the O/W interface and the surface pressure π of the film measured as a function of the area (A) over a wide range of pH (1-13) at the ionic strengths of 0.02 and 0.1. Some measurements were carried out at the interface between oil and 10 % sodium salicylate or 24 % urea. Gluten films were found to be more compressible and more stable than those of most other proteins. Pressures as high as 32 dynes/cm. (A/W) and 36 dynes/cm. (O/W) were obtained at an area of 0.2 m^2/mg, while the minimum compressibility was 0.05 cm./dyne. The extrapolated area of close-packing was 1.33 m^2/mg, at the A/W and 1.54 m^2/mg, at the O/W interface. The area of minimum compressibility was 1.1 m^2/mg, at both interfaces. At the O/W interface variation in the pH of the substrate caused differences in the degree of expansion of the films at higher areas but all the π-A isotherms between pH 1 and 12 met at about the area of minimum compressibility. The area at constant pressure (1 dyne/era.) as a function of pH gave a W-shaped curve showing minima at about pH 5.5 and 8.5 and a maximum at about pH 7.5. Variation in ionic strength from 0.02 to 0.1 had no effect on the minima; at the lower ionic strength the curve was flatter at the maximum and at the extreme ends. At pH 13 the π-A isotherm was quite different, indicating reduced cohesion in the film. The isotherm at the oil/aqueous salicylate interface was very similar to the pH 13 curve. At the oil/aqueous urea interface the isotherm was much expanded at the higher areas but met the control curve at about the area of minimum compressibility. It is concluded that spread gluten forms strongly bonded, coherent films, parts of which, when compressed below the area at which the films may be regarded as a close-packed monolayer, are displaced from the interface with relative ease and are folded up into loops. The unusually strong cohesion shown by these films may be due in part to hydrogen bonding between the numerous glutamine side chains, modified by electrostatic attraction. The rather high areas of close-packing and of minimum compressibility are probably due to the relatively high proline content of gluten.

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Additional Information:Copyright © 1960 Published by Elsevier Inc. One of the authors (N.W.T.) is indebted to the Director and the Council of the Bread Research Institute of Australia for their encouragement and provision of facilities. The initial stages of the work were carried out at the University of New South Wales.
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:52077
Deposited By: Donna Wrublewski
Deposited On:27 Nov 2014 15:00
Last Modified:03 Oct 2019 07:39

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