Hans Neukom

Diferulic acid as a possible crosslink in hemicelluloses from wheat germ.

Abstract Bound diferulic acid has been identified in small amounts in the water-insoluble pentosans of wheat endosperm. Evidence is presented suggesting that diferulic acid crosslinks adjacent polysaccharide molecules and reduces their solubility.

Dityrosine: In vitro production and characterization

Publisher Summary This chapter describes two methods for the preparation of dityrosine by peroxidase oxidation of tyrosine and N -acetyltyrosine, respectively. Using tyrosine as starting material in the production of dityrosine by the means of the peroxidase–hydrogen peroxide system, the yield of dityrosine was relatively small, higher oxidation products such as trimer and tetramer being the main products of the oxidation. Furthermore, the isolation of pure dityrosine from the incubation mixture proved to be difficult. Therefore N-acetyltyrosine is suggested as the starting material for the in vitro production of dityrosine. This derivative has the advantage of being highly water- and ethanol-soluble, which allows the production of larger amounts of the dimer in one batch. The identification of dityrosine is best done on the basis of its characteristic fluorescence. Dityrosine present in proteins can be identified after hydrolysis by amino acid analysis. The dimer behaves like a peptide and gives a relatively broad peak that elutes between phenylalanine and histidine. Newer methods for the identification of dityrosine include chromatography on a diethylaminoethanol (DEAE)-cellulose column and high-performance liquid chromatography.

Influence of different types of thermal treatment on the chemical composition and physical properties of wheat bran

The purpose of the present investigation was to submit commercially available wheat bran to various thermal treatments and to measure the resulting effects on the functional properties. Water uptake, water-binding capacity, rheological behaviour in the Farinograph and oil absorption of boiled, steam-cooked, autoclaved, roast, micronised and extruded bran were determined. The water uptake of the modified samples was increased, compared with that of the untreated bran. Only boiling affected the water-binding capacity significantly. The largest effects of the thermal modifications were rheological changes as observed in the Farinograph. Doughs, consisting of 80% patent flour and 20% wheat bran, showed a diminished maximum resistance and a prolonged mixing time compared with a standard dough with long patent flour. Wet heat treatments altered the surface of the wheat bran, resulting in a change in the oil absorption capacity.

Effect of galactose content on the solution and interaction properties of guar and carob galactomannans

Abstract Guar galactomannan has been modified by treatment with an α- d -galactosidase A preparation from lucerne seeds. This enzyme was purified by affinity chromatography on N -ϵ-aminocaproyl-α- d -galactopyranosylamine linked to Sepharose 4B, had a high activity towards galactomannans, and was completely devoid of β- d -mannanase. On incubation for 2 h, this enzyme removed ⪢ 75% of the galactose from guar galactomannan with no concurrent decrease in viscosity. Eventual decrease in viscosity was associated with the formation of insoluble, mannan-type precipitates. This phenomenon, although directly related to the galactose content of the galactomannan, was also time-dependent. The limiting viscosity numbers calculated for the “mannan backbones” of α- D -galactosidase-treated, guar galactomannan having galactose-mannose ratios of 38:62 to 15:85 were the same. Modified, guar galactomannan (at 0.4% w/v) having a galactose-mannose ratio of 20:80, or less, forms a gel on storage at 4° over several weeks. Also, gel particles form when solutions of these galactomannans are passed through a freeze-thaw cycle. Samples containing ⪡ 10% of galactose rapidly precipitate from solution even at 30°. The interaction of guar galactomannan with xanthan is greatly increased by removal of galactose residues. Samples having galactose-mannose ratios of ~19:81 interact with xanthan to essentially the same degree as carob galactomannan (Gal/Man = 23:77).

Hydroxyproline-galactoside as a protein-polysaccharide linkage in a water soluble arabinogalactan-peptide from wheat endosperm

Abstract A water-soluble arabinogalactan-peptide from wheat endosperm was degraded by treatment with mild acid, alkali and enzymes. 4-Hydroxyproline-galactoside was isolated from the degradation products and was shown to be identical with synthetic trans-4-hydroxyproline-β- d -galactopyranoside. This linkage compound connects the arabinogalactan side chains to the peptide core in the arabinogalactan-peptide. A possible structural model for this glycoprotein is discussed.

Chemical composition and physical properties of modified dietary fibre sources

Abstract The influence of thermal treatments on the chemical composition and the physical properties of yellow pea hulls, apple pomace and depectinised apple pomace were determined. The chemical composition of yellow pea hulls and apple pomace was altered only slightly. With depectinised apple pomace, however, the heat treatments led to a significant loss of the total dietary fibre (TDF) content. Water uptake, water binding capacity, rheological behaviour in the farinograph and oil absorption were determined before and after boiling, autoclaving and extrusion cooking. The physical properties of all samples were considerably affected by the thermal modifications. Whilst in cooked dietary fibre samples the water uptake, the water binding capacity and the oil absorption was always enhanced, the influence of autoclaving and extrusion cooking on the physical properties depended very much on the dietary fibre source. Yellow pea hulls showed unchanged or slightly increased values, while the results for the two apple pomace preparations were lower compared with the untreated samples. The differences in the farinogramsiwere less obvious since the dietary fibre content in the dough mixtures was only in the range of 10–20%.

Structural investigations of an arabinan from grape juice

Abstract An arabinan has been isolated from grape juice and purified by chromatography on polyamide and repeated ethanol precipitations. The structural identity of the arabinan was established by enzymatic degradation of the polysaccharide with a purified α-L-arabinofuranosidase and methylation analysis. The results obtained suggest that the arabinan consists of an α(1 → 5)-linked backbone of L-arabinofuranosyl residues to which sidechains of L-arabinose are attached in the 3-position.

Oxidative Crosslinking of Proteins and Other Biopolymers

Covalent crosslinking of biopolymers has a stabilising effect of the three-dimensional structure of the polymer. This results in profound changes in physical and biological properties of polymers. The importance of crosslinking in biology has been demonstrated at a recent ACS-Symposium on protein crosslinking.1

Electrophoretic separation of sugars and hydrolysates of polysaccharides on silylated glass-fibre paper.

Abstract The suitability of silylated glass-fibre paper as a supporting material for the electrophoresis of sugars and hydrolysates of polysaccharides has been studied. Because of the absence of molecular sieving effects by the supporting material, the separation is based only on differences in the molecular charge of the samples. The method described allows the separation of low- and high-molecular-weight substances in the same run. A mixture of seven sugars was separated into single components within 45 min. To demonstrate the versatility of the method, various polysaccharide hydrolysates were separated electrophoretically. As electrophoresis is based on a different separation principle than chromatographic techniques, this method is considered to be an efficient alternative and/or complement to the chromatography of carbohydrates.

Water content of human articular cartilage and its determination by gas chromatography

Abstract A method for the determination of the water content in cartilage was investigated. Methyl alcohol was used to extract the water from the tissue and using gas chromatography the latter was quantitatively determined. This method is suitable for cartilage quantities of 50 mg or more (wet weight) and was employed to determine the changes caused by aging in normal and osteoarthrotic cartilage from the femoral head.