Rheological studies of aqueous amylose gels: the effect of chain length and concentration on gel modulus

Abstract

Aqueous amylose gels have been studied kinetically and at pseudoequilibrium as a function of polymer concentration and chain length. Pseudoequilibrium gel moduli (G′) for a range of amylose chain lengths (produced by enzymatic synthesis) show the same concentration dependences as other gelling biopolymers and have been analyzed by the method of Clark and Ross-Murphy (Br. Polym. J. 1985, 17, 164-168). This treatment is shown to lead to the accurate prediction of critical gelling concentrations and suggests that the cross-linking functionality of individual amylose chains is ∼DP/100 (DP = degree of polymerization). For a fixed concentration, shorter chain amylose systems are found to develop turbidity more rapidly and to attain higher final values, suggesting that decreasing amylose chain length results in more heterogeneous gel structures. The relative rates of turbidity and modulus increase for amylose gels are found to be dependent on chain length: for short chains (DP < 300) turbidity precedes gelation, whereas for longer chains (DP < 1100) gelation occurs before significant increase in turbidity.