Abstract The actions of ammonium persulfate on (feruloylated) sugar-beet pectins and ferulate have been studied by spectrophotometry, viscometry, 1H-n.m.r. spectroscopy, and gel-permeation chromatography. The reactions followed a pseudo-first-order law with respect to pectin and ferulate, whereas the order with respect to ammonium persulfate was unity for pectins and varied from 0.5 to > 2 for ferulate. The rate constants mainly varied with the pH of the reaction mixture and there was an optimum at 3.8–5.7 for the gelation of the pectins. The results ruled out a simple condensation process between two ferulates (or feruloyl residues linked to the pectins) and suggeste a free-radical polymerisation reaction.