Citrate-promoted helix formation in gelatin. The viscosity-time effect

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Abstract
Citrate buffer solutions have the property of promoting viscosity increases in a number of gelatins when maintained at 20[degree] for several days, leading to values of relative viscosity several times that of the original. The behaviour with 0.15M-citrate is dependent on the pH; the maximum change in viscosity occurs near pH 7. The magnitude of the viscosity-time effect is unrelated to the molecular weight of the gelatin, above certain limits. The magnitude of the viscosity-time effect is directly related to the rigidity modulus of the gelatin. The two quantities, rigidity at 10[degree], G, and the rate of viscosity change, r, may be connected by G = K.r[alpha] It is suggested that the viscosity changes induced by citrate are due to reorientation of gelatin molecules to a collagen-type structure and that unbranched chains will revert in this way more readily than branched molecules.