The effect of neutral salts on
gelatin-gum arabic complexes*1
Noble Yoshida and Curt
Thies
The National Cash Register Company, Dayton, Ohio 45409, USA
Received 14 November 1966; Revised 16 March 1967. Available online 12 July 2004.
Abstract
Swollen gelatin-gum arabic (GGA) complexes behave like
typical polyelectrolyte gels in that observed swelling values are a strong
function of pH and neutral salt concentration. At pH 3.5 and 24°C., GGA
complexes swell very slowly in many salt solutions. True equilibrium swelling
values are never obtained in many cases. Increasing concentrations of NaCl or Na2SO4 cause GGA swelling
values to pass through a maximum, thereby giving swelling curves similar in
shape to the typical salting-in and salting-out curves frequently encountered
with proteins and polypeptides. CaCl2 concentrations as low as 0.25 M
grossly weaken and appear to partially melt GGA complexes at 24°C., whereas
higher CaCl2 concentrations (>0.75 M) rapidly destroy GGA
complexes. Irreversible swelling changes observed when GGA complexes are
subjected to cyclical swelling treatments in buffer and buffered NaCl solutions, are due to displacement of gum arabic (GA) from the complex as Bungenberg
de Jong and Landsmeer
concluded previously. Only 83% of the gum arabic
initially present in the complex can be displaced under a variety of
conditions, indicating that a substantial amount of GA is difficult to remove
from a GGA gel. This may be due to physical entrapment of GA in the gel or may
be a characteristic feature of GGA gels. The initial rate of GA displacement is
a strong function of neutral salt concentration even though marked shrinkage of
the gel occurs at higher salt concentrations. Chloride analyses show that
diffusion of salt ions into the swollen complex is rapid and does not control
the rate of GA displacement. In contrast, the large size of GA and the
multiplicity of charged groups on each GA molecule suggest that its diffusion
from the gel controls the over-all rate of displacement. Limited experiments at
17°C, suggest that decreasing the temperature from 25° to 17°C. does not noticeably affect the rate of GA displacement.
*1
Portions of this paper were presented at the Winter Meeting of the American
Chemical Society, Polymer Division,
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Journal of
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