Effect of pH on the rheological response of reconstituted gastric mucin

Abstract

The rheological response of reconstituted gastric mucin was studied by time dependent rheological experiments as function of pH. Mucin concentrations of 5% and 10% were prepared in buffer dispersions at pH of 1.15, 2.00, 2.55, 4.00 and 7.67. The isoelectric point was identified by z-potential between pH 2.00 to 2.55. Dynamic light scattering showed that as pH reduced, a second population of larger mucin aggregates was formed indicating the presence of new structures. Steady shear rheological measurements reflected the pseudoplastic behavior of mucin dispersions and the effect of concentration on viscosity. Creep-recovery measurements were performed on the regenerated mucus at different levels of pH. By creep, it was possible to determine the values of zero-shear-viscosity of mucin suspensions, with higher precision and in a lower experimental time than steady shear measurements. Additionally, it was found that at pH ~1.15, the viscosity of the mucus increased to high values, which is an indicative of a gel-like structure. By recovery experiments, it was possible to find that even the very low viscosities the mucin suspensions at pH ~1.15 possessed a defined elastic character. By the use of a four-element mechanistic viscoelastic model, it was concluded that this elasticity underwent retardation due to the combined effect of viscous and elastic responses.

Keywords

• Mucin
• rheology
• z-potential
• creep
• elasticity