Characterization of pectin lyases on pectins and methyl oligogalacturonates

Pure saturated and unsaturated oligogalacturonic acids, including unsaturated monogalacturonic acid, were isolated and characterized. Their ultraviolet absorbance at 232 run, and their reactivities in the periodate thiobarbituric acid test and carbazole tests were studied. From these compounds methyl oligogalacturonates were prepared, which were used as model substrates.Pectin lyases (EC 4.2.99.8; poly-α-1,4-D-methyl-galacturonate lyase) were found to be very common in commercial 'pectinase' preparations. From each of three 'pectinase' preparations a pectin lyase was isolated free of other pectolytic enzymes. Their pH optimum, pH stability, isoelectric point and activation energy were determined. Information on the action of the enzymes on pectins with various degrees of esterification ( DE ) was obtained by kinetic studies, by determining the extent of degradation and by analysing the composition of the reaction mixtures. The breakdown mechanism on pectin and pattern of action on methyl oligogalacturonates was studied. Divalent cations were found to activate pectin lyase activity, their activation depended on the pH and DE. Literature on the isolation and characterization of oligogalacturonides and on pectin degrading enzymes is reviewed

Phenolic compounds and related enzymes as determinants of sorghum for food use

Phenolic compounds and related enzymes such as phenol biosynthesizing enzymes (phenylalanine ammonia lyase) and phenol catabolizing enzymes (polyphenol oxidase and peroxidase) are determinants for sorghum utilization as human food because they influence product properties during and after sorghum processing. Phenolic compounds are quality-grade markers for the preparation of several foods because of enzyme inhibitory activities, color, or antioxidant activities. Large inter-varietal differences in contents of phenolic compounds and their antioxidant activities among sorghum varieties exist. Moreover, some red sorghum varieties have higher antioxidant activities than the most important sources of natural antioxidants. Oxidation products of peroxidase and polyphenol oxidase (benzoquinones and polymeric compounds) affect food quality. This paper reviews the current advances in phenolic compounds and phenolic enzymes in sorghum as human food, with emphasis on nutritional and health aspects. The suitability of sorghum varieties for food and beverages is discussed

Evaluation of computer-based learning material for food chemistry education

Digital exercises were designed and developed for food chemistry education. During the design process, design requirements were described for such exercises. The exercises were evaluated in three case studies, firstly to determine whether the exercises satisfy the design requirements with respect to students¿ use and secondly to provide insight into the effect of the course structure and organisation on the value that the students attribute to the exercises. The results show that the exercises meet most of the design requirements. Students found the exercises clear and helpful, and most students confirmed that these exercises helped them in their preparations for their examinations. Despite this, participation in the programme was low when working on the exercises was not compulsory. The differences in evaluation results between the three studies can be explained by differences in the course structure and organisatio

Магніторезистивні властивості плівкових структур на основі Fe та SiO

Мета кваліфікаційної роботи магістра полягає в встановленні закономірностей впливу розмірних і температурних ефектів на магніторезистивні властивості шаруватих структур типу «феромагнітний метал – діелектрик» Під час виконання роботи використовували вакуумну установку для конденсації плівкових зразків ВУП – 5М, установку для дослідження магніторезстивних досліджень, методи осадження тонких плівок у вакуумі. У результаті проведення наукових досліджень установлено, що магніторезистивний ефект для свіжо сконденсованих та відпалених за температури 400 К багатошарових плівок [Fe/SiO]5/П з товщиною феромагнітного матеріалу dFe = 5 – 10 нм та діелектрика dSiO = 1 – 5 нм має анізотропний характер. Величина як поздовжнього так і поперечного магнітоопору в магнітних полях до 0,6 Тл не перевищує 0,053%. Після відпалювання зразків за Твідп=400 К, як характер магнітоопору так і величина поздовжнього та поперечного магнітоопору не змінюється

Cloning and characterization of arabinoxylan arabinofuranofydrolases-D3 (AXHd3) from Bifidobacterium adolescentis DSM20083

Arabinoxylan arabinofuranohydrolase-D3 (AXHd3) from Bifidobacterium adolescentis releases only C3-linked arabinose residues from double-substituted xylose residues. A genomic library of B. adolescentis DSM20083 was screened for the presence of the axhD3 gene. Two plasmids were identified containing part of the axhD3 gene. The nucleotide sequences were combined and three open reading frames (ORFs) were found. The first ORF showed high homology with xylanases belonging to family 8 of the glycoside hydrolases and this gene was designated xylA. The second ORF was the axhD3 gene belonging to glycoside hydrolase family 43. The third (partial) ORF coded for a putative carboxylesterase. The axhD3 gene was cloned and expressed in Escherichia coli. Several substrates were employed in the biochemical characterization of recombinant AXHd3. The enzyme showed the highest activity toward wheat arabinoxylan oligosaccharides. In addition, -xylanase from Trichoderma sp. was able to degrade soluble wheat arabinoxylan polymer to a higher extent, after pretreatment with recombinant AXHd3. Arabinoxylan oligosaccharides incubated with a combination of recombinant AXHd3 and an -l-arabinofuranosidase from Aspergillus niger did not result in a higher maximal release of arabinose than incubation with these enzymes separately

Agro-materials : a bibliographic review

Facing the problems of plastic recycling and fossil resources exhaustion, the use of biomass to conceive new materials appears like a reasonable solution. Two axes of research are nowadays developed : on the one hand the synthesis of biodegradable plastics, whichever the methods may be, on the other hand the utilization of raw biopolymers, which is the object of this paper. From this perspective, the “plastic” properties of natural polymers, the caracteristics of the different classes of polymers, the use of charge in vegetable matrix and the possible means of improving the durability of these agro-materials are reviewed