The Effect of pH on the Rheological Properties of the Mixed Gels of Acylated Gelatin and Agarose

Abstract

The effect of pH on the dynamic Young's modulus E' of the mixed gels of acylated gelatin and agarose was investigated. Two samples of acylated gelatin showed isoionic point 5.5 and 8.8, respectively. The values of the intrinsic viscosity of the two samples were 2.0 and 5.5 at 35°C in 0. 01 N-KSCN. The concentration of acylated gelatin was varied from 2 to 18% (w/w) in the mixed gels with low molecular weight agarase, and was varied from 3 to 12% (w/w) in the mixed gels with high molecular weight agarose. The concentration of agarose was fixed as 1% (w/w) in all the cases. The values of pH of the mixed gels were 4.0 and 9.2, respectively. When the pH of the mixed gel was far different from the isoionic point, the value of E' of the mixed gel of 3% (w/w) acylated gelatin and 1% (w/w) agarose showed the maximum below 30°C. When the concentration of the acylated gelatin was higher than 10% (w/w), E' decreased rapidly for the mixed gel containing gelatin of isoionic point 5.5 and gradually for the mixed gel containing gelatin of isoionic point 8.8, with increasing the concentratian of gelatin. For the mixed gel containing 3% (w/w) acylated gelatin, the observed values of E' of mixed gels were larger than the estimated ones by a theory on dispersed systems when the pH of the mixed gels was far different from the isoionic point. The situation was opposite for the mixed gel whose pH was near to the isoionic point.