Mucoadhesion of pectin as evidence by wettability and chain interpenetration

Different types of pectin were characterized for gastrointestinal (GI) mucoadhesion. The mechanisms of mucoadhesion of these pectins were investigated by measurements of surface tension, contact angle, and FTIR studies. The surface tension of different GI fluids was relatively the same and found to decrease after addition of mucin. The contact angle of tested fluids on pectin surfaces behaved as time-dependent and the values at 30 s were used for comparison. The type of pectin, addition of mucin and pectin surfaces influenced the contact angle of GI fluids. The thermodynamic work of adhesion (Wad/therm) and spreading coefficient were calculated. The positive values of Wad/therm indicated that the pectin surfaces could be wet spontaneously by adhesional process. The pectin with higher molecular weight and higher degree of substitution showed a lower Wad/therm, resulting from the low wettability. The spreading coefficient of tested fluids containing mucin on pectin surface was negative, suggesting that no spreading could be occurred spontaneously. ATR-FTIR studies revealed the changes resulting from interpenetration of pectin–mucin chains at film interface and the formation of hydrogen bonds. The results obtained from this study demonstrated that the wetting behavior and work of adhesion could be used to explain the mechanism of mucoadhesion of various pectins in GI conditions, and that a chain interdiffusion occurred at the interface of pectin film and mucin solution which supported the diffusion theory of mucoadhesion.