Enzymatic hydrolysis of [beta]-casein and [beta]-lactoglobulin : foam and emulsion properties of peptides in relation to their molecular structure

Peptides derived fromβ-casein (βCN) andβ-lactoglobulin (βLg) were analysed for their foam- and emulsion-forming and -stabilising properties (further denoted functional properties) and for their structural characteristics in order to elucidate structure-function relationships.βCN was hydrolysed by plasmin and subsequent fractionation of the hydrolysate resulted in various hydrophilic, amphipathic and hydrophobic peptide fractions with clear differences in functional properties. The highly-charged N-terminal part of the amphipathic peptides appeared to be important for the emulsion-stabilising properties ofβCN peptides. The main secondary structure element ofβCN(-peptides) in solution was the unordered random coil, but upon adsorption onto an hydrophobic interfaceα-helix was induced. The hydrophobic C-terminal part ofβCN accounted for the high maximum surface load on the interface, while the N-terminal part ofβCN seemed to be responsible for theα-helix induction upon adsorption. No clear relation between the secondary structure and the functionality was observed in this system but a relation between a high surface load and good stabilising properties seemed to exist.BovineβLg was hydrolysed by the action of trypsin, plasmin and Staphylococcus aureus V8 protease. Overall, the plasmin hydrolysate had the best functional properties at pH 6.7, compared to the other hydrolysates and was investigated further. DuringβLg/plasmin hydrolysis significant SH/SS-exchange has taken place yielding a large number of different peptides. The peptides present were (1) peptides composed of a single amino acid chain lacking a cysteine residue, (2) peptides composed of a single amino acid chain containing intramolecular disulphide bonds and (3) peptides composed of 2 amino acid chains linked by an intermolecular disulphide bond. The occurrence of the SH/SS exchange and the homogeneous distribution of charge and hydrophobicity hinder an efficient fractionation of the hydrolysate.In conclusion, the production of specific peptides and peptide fractions is more complicated forβLg than forβCN, mainly because of the differences in primary structure (such as the distribution of charge and hydrophobicity) between the proteins. The foam- and emulsion-forming properties of peptides can be superior to those of intact proteins, as long as they have both charged and hydrophobic areas. The foam- and emulsion-stabilising properties of peptides depend highly on the amount of repulsion they can produce (either by a strong amphipathicity or by a high surface load).</p

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

The adsorption-induced secondary structure of β-casein and of distinct parts of its sequence in relation to foam and emulsion properties

Changes in the secondary structure upon adsorption of β-casein (βCN) and of distinct parts of its sequence were investigated by far-ultraviolet circular dichroism in order to find suggested relationships with foam and emulsion-forming and -stabilising properties of the same protein/peptides. A teflon/water interface was used as a model system for foam and emulsion interfaces. The maximum surface loads of β-casein and its derived peptides were investigated. The main secondary structure element of all samples in solution was the unordered random coil, but upon adsorption ordered structure, especially α-helix, was induced. At lower pH more ordered structure was induced, just as at lower ionic strength. Apparently, both hydrophobic and hydrophilic groups influence the change of secondary structure induced at a hydrophobic interface. The results suggest that the hydrophobic C-terminal half of βCN accounted for the high maximum surface load on teflon, while the N-terminal half of βCN seemed to be responsible for the secondary structure induction upon adsorption. A relation between the maximum surface load and the foam-stabilising properties was found, but an influence of the secondary structure properties on the foam and emulsion-forming and -stabilising properties was not observed. Copyright (C) 1999 Elsevier Science B.V