ENZYMATIC AND CHEMICAL DEGRADATION OF SOME INDUSTRIAL PECTINS

Three industrial high-methoxyl pectins purified by copper precipitatio n have been degraded by acid, chemical beta-elimination and endopolyga lacturonase. Degraded pectins from beta-elimination and enzyme treatme nts have been fractionated by preparative SEC and the resulting fracti ons have been analysed for their neutral-sugar, protein and phenolic c ontents. Distribution of neutral sugars indicates that the model of al ternating 'hairy' and 'smooth' regions is also valid for industrial pe ctins. Most of the phenolics present in the copper-purified samples ar e probably not bound to the pectin molecules except for a small propor tion that was found to be associated with the segments rich in neutral sugars. Proteins are associated with the hairy regions. Relative prop ortions of the oligomers with DP up to 17 produced by the action of en doPG and analysed by high-performance ion exchange chromatography were compared with a theoretical distribution model. The abundance of mono -, di- and trigalacturonides suggests that. in the smooth regions of i ndustrial pectins, free carboxyl groups are present as blocks of non-e sterified galacturonide units. HPSEC elution patterns of acid-degraded samples suggest that homogalacturonan blocks of average degree of pol ymerization of 40-60 are interspaced by rhamnose units. Degradations b y beta-elimination and endoPG indicate that most of the rhamnose units are concentrated in the regions carrying the side chains. This would mean that the pectin backbone consists of rhamnogalacturonan regions a lternated with homogalacturonans regions, the homogalacturonan regions being interrupted at regular intervals by rhamnose units.