Cross-linking of amidated low-methoxylated pectin with calcium during extrusion/spheronisation: Effect on particle size and shape

Granulation and pelletisation by wet extrusion/spheronisation is a well-known technique for particle design in the pharmaceutical industry. The objective of this study was to evaluate the use of amidated low-methoxylated (LM) pectin as an excipient for pelletisation by extrusion/spheronisation. The influence of degree of amidation of pectin (14%, 18% and 24%) and concentration of added calcium ions (0%, 5%, 12% w/w) on the shape and size of pectin pellets was investigated. The chosen approach was to aim at cross-linking during processing which could be obtained by adding calcium ions to the amidated pectin in the powder mixture and perform granulation/extrusion with water. Addition of calcium ions was expected to reduce the solubility and swelling of pectin during processing, and, consequently, the roundness of the pectin pellets should be improved. Both the degree of amidation and the concentration of added calcium ions as well as the interaction between the two were identified as significant factors in preparation of spherical pellets. The results suggest that the egg-box model alone cannot describe the cross-linking between amidated LM pectin and calcium ions, and it is proposed that the amid group itself plays an important role in the system.