Pectic substances–water. I. Structural changes in the polygalacturonide chains during water adsorption

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Abstract
An apparatus suitable for studying adsorption of water vapor both volumetrically and gravimetrically is described. Water vapor isotherms of highly esterified pectin, sodium pectate and pectic acid were determined. Equatorial and meridional spacings of the x‐ray diffraction patterns were measured as a function of equilibrium water content in these materials. The interchain separations, as measured by the changes in the equatorial spacings of x‐ray reflections, follow the shape of the adsorption isotherms. In esterified pectin and sodium pectate, the fiber repeat period increases until 5 molecules of water content per 3 galacturonide residues are adsorbed, thereafter remaining constant. The fiber period of pectic acid is constant throughout water adsorption.

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