Study on the mucoadhesion mechanism of pectin by atomic force microscopy and mucin-particle method

Atomic force microscopy (AFM) has been used to probe the interaction between porcine stomach mucin and a mucoadhesive polymer, pectin, with different chemical characteristics. Images were produced detailing the structures of mucin, pectin and the mixtures of pectin and mucin, in either 0.1 N hydrochloric acid or deionized water. The AFM images of the pectin–mucin mixture in acidic medium showed no association between pectin and mucin. The large aggregates observed after mixing pectin and mucin in deionized water revealed the association between pectin and mucin, probably by the H-bonding. Increasing of pectin in the mixture with mucin resulted in a shift of zeta potential of the mixture to a higher negative value. The electrostatic repulsion with the same charges of pectin and mucin may cause an uncoiling of polymer chains, which facilitated chain entanglement and bond formation. The particle size of the mixtures of pectin and mucin depended on the proportion of either pectin or mucin in the mixture. The results suggested that the mucoadhesion of pectin could be due to the adsorption mechanism on the mucin molecules or electrostatic repulsion between pectin and mucin.