Amidated pectins-characterization and enzymatic degradation

Partially amidated pectins with degrees of amidation between 10 and 40% are prepared by de-esterification with ammonia in the heterogeneous phase. The mol. wt distribution monitored by gel permeation chromatography (GPC) has been hardly changed by this procedure. From measurements of intrinsic viscosities of GPC fractions it is concluded that amidated groups have no effect on molecular shape in solution (ionic strength 0.1). The Mark-Houwink equation for pectins obtained formerly [eta] = 0.0955 M(w)(0.73) can also be applied to partially amidated pectins. In ion exchange chromatography the fractionation depends only on the share of free carboxyl groups in the pectin molecules, Both amidated and esterified carboxyl groups in the units of the pectin chain are detected in a similar manner, they are not discriminated. At the beginning of enzymatic hydrolysis the activity of polygalacturonase is not essentially reduced by amidated groups if pectinesterase activity is sufficient. Hydrolysis of amidated pectins with an excess of pectolytic enzymes and long reaction times is restricted to the amount of non-amidated groups. No long-range effects of amidated units are observed.