Stability and rheology of plant-derived hydrocolloid-mucin mixtures

Mixtures of mucin with pectin were investigated in a range of pectin to mucin ratios and pH values. The phase stability was first studied as absorbance measured at 500 nm (turbidity). Co-existence of the two materials did not result in co-sedimentation or relevant phase separations, while lower pH enhanced aggregation and partial sedimentation of individual components, especially for mucin. The above are in line with the recorded zeta potential values, which are negative for both components at neutral pH and drop down to almost zero at acidic values. The sizes of the particles, as recorded by dynamic light scattering, show a similar trend to the absorbance values, indicating that phase separations are in line with events at the scale of a few hundred nm. Such interactions reflect in shear rheology: The viscosity corresponding to 50 s^-1 decreases upon substitution of pectin with mucin at pH 7 and 3, suggesting a flow dominated by changes in the space occupancy by the two components and by changes in the size of the self-assembled structures. The results were compared with those of more complex and typical hydrocolloids extracted from olive compost: The overall shape of the stability diagram of the two ingredients match, suggesting similar modes of action in the presence of mucin for other natural materials. These data throw some light in the norms during the co-existence of food polysaccharides and mucin in oral and gastrointestinal environments.