Polysaccharides in rapeseed and effects of enzymes on wheat arabinoxylan during breadmaking.
1997
Eriksson I.
Variations in the main components of whole seed were studied in 36 varieties of rape- and turnip rapeseed. Yellow-seeded varieties were characterised by low Klason lignin content. Oil and protein content was negatively correlated and the content of neutral dietary fibre (DF) polysaccharide residues in the seeds primarily varied in unison. DF contents as analysed by three methods were correlated but at different levels. Klason lignin content in whole seed was positively correlated to hull content. There were considerable differences in DF composition between polysaccharide isolated from dehulled rapeseed meal. The main structural features of this high-molecular weight polysaccharide were shown to be those of a highly branched arabinan fragment containing terminal and 2, 5-linked arabinose residues. The water-insoluble residue from dehulled rapeseed meal was extracted with ten different procedures using different extracting agents (CDTA or buffer), pH and ionic strength. Highest yield of pectic substances was extracted with CDTA at pH 6.5. Subsequent extractions with Na2CO3 at pH 10 partly extracted a different population of pectin. Dough and breadcrumb samples were prepared from wheat flour supplemented with a commercial enzyme preparation for baking containing mainly endo-beta-1,4-xylanase activity. Enzyme addition caused an increase in the water-extractability of the arabinoxylan, coinciding with an increase in loaf yield. The enzyme seemed mainly to solubilise previously water-unextractable arabinoxylans, but also showed some ability to degrade high molecular size arabionoxylan fragments into smaller fragments, although not to oligosaccharide size. Effects on wheat dough arabinoxylan were compared for four different enzyme-preparations. All four enzymes released arabinoxylan fragments from the water-unextractable arabinoxylan fraction. For two of the enzymes, this effect was substantially increased in the presence of yeast, although no effect was observed when yeast was added alone. Preference to release differentially substituted arabionoxylan fragments was also observed.
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