Interactions between mucin and okra gum during pH cycling

Abstract

Solutions of okra gum and mucin were studied during pH cycling (7–3–7), as to model the interactions between these components in the oral-gastrointestinal tract. Okra gum aggregates with mucin at pH close to 3, while they redissolve back at pH 7 due to electrostatic interactions. Fluorimetry shows that complexes form at low pH, and break-up upon return to pH 7. At pH 3 both static and transient complexes are detected. Shear viscosities reduce upon pH lowering from 7 to 3 pH 3 and then are partially restored back at pH 7, suggesting a hysteresis in the macromolecular rearrangement after pH cycling. Hysteresis is more pronounced in the extensional rheology, leading to Trouton ratios with a strong dependence on the pH. Thus flow can be regulated in different ways in compartments with different pH (mouth, stomach, intestine).