A dynamic rheological method to study the interaction between starch and lipids

Abstract

A dynamic rheological method was used to follow transitions occurring during heating and cooling of starch–lipid gels that were prepared separately from the rheological measurement. A decrease in storage modulus (G′) and a simultaneous increase in phase shift (δ) were interpreted as due to a transition of the amylose–lipid complex. During cooling an increase in G′ and a decrease in δ were observed. The temperature of this transition (Tm) was found to depend on the type of starch, chain length of complexing ligand, polar head group of the ligand, and salt concentration for ionic ligands. For a hydroxypropylated potato starch lower Tm values were observed than for the native potato starch. Surfactants with longer hydrocarbon chains gave higher Tm values. The polar head influenced the stability so that it increased in the following order: cationic<anionic<nonionic. For the charged ligands Tm increased with the concentration of NaCl. This was explained as due to a generic electrostatic effect of ions on the helix–coil transformation. Not only the transition of the amylose–lipid complex was affected as described. Also the rheological properties of the starch–lipid gel at room temperature were possible to change depending on the ligand used. By combining the proper starch and surfactant/emulsifier it was thus possible to obtain very strong and elastic gels (i.e., high G′ and low δ values) or very weak and viscous gels (i.e., low G′ and high δ values).