Enzymatic modification of pectic polysaccharides obtained from sugar beet pulp

摘要

Rhamnogalacturonans and arabinans, purified from an autoclave extract of sugar beet pulp, as well as an acid extracted beet pectin (ABP) were treated with enzymes in order to modify their physico-chemical properties. The enzymes used were arabinofuranosidase B (AF), endo-arabinanase plus arabinofuranosidase (EA + AF), rhamnogalacturonase plus rhamnogalacturonan acetyl esterase (RGase +RGAE), and polygalacturonase plus ectin methyl esterase (PG + PE). During the enzyme treatments the intrinsic viscosity ([#eta#]_w), apparent molecular weight (M_w), and radius of gyration (Rg_w) of the polysaccharides were monitored. We found in most cases that treatment with glycanases decreased the [#eta#]_w of the polysaccharides investigated. However, results showed that degradation of the rhamnogalacturonan backbone of a beet pectin obtained by acid extraction had little influence on the [#eta#]_w which led to the conclusion that the rhamnogalacturonans present in this type of pectin are mainly located at the extremities of the pectin molecules. Some evidence was found that the rhamnogalacturonans obtained by autoclaving are linked through the arabinose side-chains, probably by diferulic acid cross-links. Removal of the side-chains of the arabinans present in the rhamnogalacturonant=s of ABPs with enzaymes also showed that the arabinan side-chains contribute relatively litle to the [#eta#]_w. In our experiments we found that modificaion with glycanases can be used to change the structural characteristics of pectic polysaccharides without a signficant loss of viscosity. In this way glycanase can be used for the removal of structural elements of pectic polysaccharides, which limit their physico-chemical properties.