The surface chemistry of wheat gluten II. Measurements of surface viscoelasticity

A Comparative Study of the Monolayers of Various Cereal Proteins and of Wheat Glutens of Differing Characteristics

“…An examination of the chemical" and physi~al changes occurring in wheat gluten on dispersion in" anhydrous and aqueous acid chloroethanol (Tschoegl 1961) had shown that partial esterification of free carboxyl groups and a slight loss of amide nitrogen occurs when gluten is dispersed in a 0 ·IN solution of hydrogen chloride in anhydrous chloroethanol while this does not occur in a O'OlN solution of hydrochloric acid in chloroethanol containing 30% water. The isoelectric point of gluten films spread from the latter dispersions was found to be 6·7 (Tschoegl 1961) while surface viscosity measurements on gluten films spread from anhydrous acid chloroethanol yielded an isoelectric point of 7·5 (Tschoegl and Alexander 1960b). Aqueous dispersions gave lower surface viscosities than anhydrous dispersions but in all other essential respects gluten films spread from these two different dispersants seemed to be identical.…”

“…If it is true that this increase reflects bond formation in the film (Tschoegl and Alexander 1960b) differences in the cohesiveness of the cereal "glutens" might possibly show up in this time dependence. Strong wheat and oat (defatted), representing the extreme placings of the cereals in the rank order referred to above, were therefore selected for a detailed study.…”

“…Figure 2, therefore, shows plots of the absolute surface modulus (a., dyn/cm), a combination of 7Js and Gs (Tschoegl and Alexander 1960b), against area. In order of increasing modulus at the same area the films fall in the order: strong wheat, weak wheat, rye, barley, oat, carob.…”

“…Since the surface viscosity hs, surface poise) and surface rigidity (G., dynjcm) of wheat gluten had shown a marked dependence on the pH of the substrate (Tschoegl and Alexander 1960b) a study of this effect was made on the same extracts by measuring 7Js and Gs as a function of the area at the OjW interface. These measurements were carried out at pH 6·8 and 2·1 at an ionic strength of 0·1.…”

“…The areas at which the films were spread were chosen to yield comparable limiting viscosities. The experimentally determined values were fitted by the method of "internal least squares" (Hartley 1948) to the relation (Tschoegl and Alexander 1960b):…”