Extensional and shear rheology of a food hydrocolloid

A shear and extensional rheological profiling of okra mucilage is presented, comprising the results of measurements at pH 7.0 and at pH 4.0, as to obtain information on this hydrocolloid's mechanical and self-assembly properties, along with supporting data from nanoparticle tracking analysis. The results are compared to new data on the extensional viscosity of another hydrocolloid, carboxymethyl cellulose (CMC). The okra materials under study do not comply with the CoxeMertz rule, while their rheographs do not show concentration-independent scaling behavior. The obtained relaxation times, shear and extensional moduli, and shear and extensional viscosities, are used as to draw conclusions on the self-assembly and conformations of the okra macromolecules comprising the mucilages. Their rheology is dominated by extensional viscosity, as the Trouton ratios are in the order of tens to hundreds for all concentrations and at both pH values, while they decrease with increasing concentration. The above suggest that only a combination of the shear and extensional data can account for the slimy and particular mechanical character of okra mucilage solutions. (C) 2017 Elsevier Ltd. All rights reserved.