Investigating network, branching, gelation and enzymatic degradation in pectin by atomic force microscopy

The molecular structures of pectin networks and gels have been imaged using atomic force microscopy (AFM). All the samples were deposited from aqueous solution onto the surface of freshly cleaved mica, air dried, and then imaged under butanol. The interactions between Ca++ ions (two concentrations of 1 mM and 1 M) and pectin molecules were described by AFM images. Addition of Ca++ ions into aqueous solution of low-methoxyl pectin caused gelation by means of salt linkages between the carboxyl groups of adjacent pectin molecules. Increasing the Ca++ ion concentration resulted in secondary aggregation. Degradation of pectin by pectolytic enzymes was also visualised by the AFM. Image after depectinization clearly showed that main chain and branched blocks of pectin were completely split into single galacturonic acid units, whereas pectolytic enzymes remained unchanged.