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Buckwheat seeds are an important pseudocereal used as flour in baking industry. Also hulls, a waste material produced in the de-hulling process is of certain interest. Hemicelluloses were isolated from buckwheat hulls. They were characterised and shown to be of the glucuronoxylan type. Their effect upon rheological properties of gels of corn starch with varying amount of hemicelluloses (0.3%; 0.5%; 0.7% and 1.0%) is described. The rheological properties of the blends were investigated using the Brabender viscograph and Rheotest 2 viscograph. At the same pasting temperature, pastes containing an optimum of hemicelluloses (0.5-0.7%), exhibited the highest viscosity and stability against mechanical stress. At this optimum concentration, hemicelluloses increased substantially the apparent viscosity of the pastes at low and high shear rates and this trend was observed also with increase in temperature. Effect of the hemicellulose addition to corn starch on retrogradation of the pastes was studied in the refrigeration as well freeze-thaw processes. A minimum addition of hemicelluloses (0.3%) significantly affected the syneresis of starch.
Cereal hemicelluloses are plant cell wall polysaccharides which have a great influence on the processing and quality of starch-based food products due to the interactions between these polysaccharides. In this paper the influence of hemicelluloses isolated from non-food sources i.e. 4-O-methylglucuronoxylan from beech wood and arabinoglucuronoxylan from corn cobs on the rheological and pasting properties of corn and potato starches. A series of blends was prepared from the two starches in combination with both hemicellulose types added in concentration range of 1.0 to 2.0%. The rheological properties of the blends were characterised by flow curves and the rétrogradation of starches/hemicellulose blends were investigated on the refrigeration and freeze-thawing. Both types of hemicellulose exhibited a significant, positive effect on the syneresis of starch at its ~2% concentration.
Dietary fibres (DF) have been isolated from rapeseed and peas, separated into different fractions and investigated for their content of associated non-carbohydrate compounds, especially proteins by UV-spectroscopy, nitrogen determination, isoelectric focusing, and rocket Immunoelectrophoresis. The level of protein varied according to the plant origin of DF and among the different DF fractions (pectins, hemicelluloses, cellulose, lignins). In general, rapeseed DF contained more protein than pea DF, with the hemicellulose fraction from rapeseed hulls having the highest level. Rocket immunoelectrophoresis proved the presence of myrosinase as part of the DF associated proteins in rapeseed. This may be of importance for the degradation of glucosinolates in the digestive tract of humans and animals, and thereby the effects from these compounds are changed.
Tannins are water-soluble polyphenolic compounds found in plants as secondary metabolites. The presence of these substances in the barks of eight different plants was initially examined and their crude extracts were used separately as a substrate for production of tannase through submerged fermentation by Bacillus licheniformis KBR6. Tannase production as well as biodégradation of the substrate reached a maximum within 15 to 18 h against crude tannin extract obtained from Anacardium occidentale. Among different concentrations of the crude tannin tested, 0.5% (w/v) induced maximum synthesis of enzyme. Tannase production was higher by almost two-fold in the presence of crude tannin compared to pure tannic acid used as a substrate. It seems that industrial production of tannase, using bark extract of A. occidentale can be a very simple and suitable alternative to presently used procedures.
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