AbstractIn this paper, the efficiency and mechanisms of two pectinases (pectate lyase (PL) and alkaline pectinase (AL)) to hydrolyze model pectic substances and dissolved and colloidal substances (DCS) of Masson pine bleached chemithermomechanical pulp (BCTMP) were investigated. The cationic demand values of model polygalacturonic acid and DCS could be reduced to about 20% and 60 to 70% by these two pectinases, respectively. However, due to the unmethylated form of the pectic substances in DCS of BCTMP, PL is more efficient than AL. The hydrolysis mechanism of polygalacturonic acid with PL was investigated. The results showed that there was no need to hydrolyze the polymeric pectic substance to their monomers, since a minimum average degree of polymerization (DP) of 6.0 was required for pectic acid to interact strongly with cationic polymers and reduce the efficiency of the latter.