Laetitia Canabady-Rochelle

Determination of reducing power and metal chelating ability of antioxidant peptides: Revisited methods

The purpose of this study was to improve two common tests used for antioxidant capacity measurements, i.e. the reducing power and chelating ability measurements, for appropriate comparisons between the molecules tested and chosen references, as the usual methods are often performed in a qualitative way rather than a quantitative way. After revision, it was then possible to determine an AERC indice (Ascorbate Equivalent Reducing Capacity) and a CECC (Carnosine Equivalent Chelating Capacity) or EECC (EDTA Equivalent Chelating Capacity) indice according to the standard chosen, by analogy to the TEAC indice (Trolox Equivalent Antioxidant Capacity) already used in many reported works to determine the free radical scavenging activity. Thus, the determination of these relative indices enables the comparison of antioxidative capacities obtained in various studies. The adaptation of these two tests to micro-scales and the calculation of AERC, EECC and CECC were performed on model peptides.

Effect of Meso vs Macro Size of Hierarchical Porous Silica on the Adsorption and Activity of Immobilized β-Galactosidase

β-Galactosidase (β-Gal) is one of the most important enzymes used in milk processing for improving their nutritional quality and digestibility. Herein, β-Gal has been entrapped into a meso-macroporous material (average pore size 9 and 200 nm, respectively) prepared by a sol-gel method from a silica precursor and a dispersion of solid lipid nanoparticles in a micelle phase. The physisorption of the enzyme depends on the concentration of the feed solution and on the pore size of the support. The enzyme is preferentially adsorbed either in mesopores or in macropores, depending on its initial concentration. Moreover, this selective adsorption, arising from the oligomeric complexation of the enzyme (monomer/dimer/tetramer), has an effect on the catalytic activity of the material. Indeed, the enzyme encapsulated in macropores is more active than the enzyme immobilized in mesopores. Designed materials containing β-Gal are of particular interest for food applications and potentially extended to bioconversion, bioremediation, or biosensing when coupling the designed support with other enzymes.

Computational study on the molecular conformations of phenolic compounds

The study of the conformation of eight phenolic compounds (i.e. phenol, guaiacol, syringol, pyrocatechol, o-, m-, p-cresol and vanillin) was carried out using B3LYP (Becke, 3-parameter, Lee-Yan-Parr) method and cc-pVTZ (correlation consistent polarized polarisation Valence triple zêta) basis set. Potential energy surfaces were plotted in order to identify the minimum energy structures and the transition states. For the first time, structures of vanillin and syringol were completely determined. Moreover, our work also confirms that the most stable conformations of m-cresol and p-cresol are obtained when the methyl group presents a hydrogen atom at the perpendicular of the benzene ring. The possibility of intramolecular hydrogen bonding was also investigated. Guaiacol, pyrocatechol, syringol and vanillin present a structure stabilized by the presence of a moderate hydrogen bond. Finally, potential energy barriers and rotational potential functions were calculated. The comparison of the rotational potential parameters for each molecule highlights the presence of similarities specific to each substituent and their neighbours.

SPR screening of metal chelating peptides in a hydrolysate for their antioxidant properties

There is a growing need in the industrial sector (health, nutrition and cosmetic) to discover new biomolecules with various physico-chemical and bioactive properties. Various beneficial effects of peptides - notably those produced from protein hydrolysis - are reported in the literature. The antioxidant activity involves various mechanisms, among them metal chelation, studied by UV-visible spectrophotometry. In this paper, we set up an original method of screening metal chelating peptides in a hydrolysate using Surface Plasmon Resonance (SPR) for their antioxidant properties. To date, the empirical approach used several cycles of hydrolysate fractionation and bioactivity evaluation until the isolation of the pure bioactive molecule and its identification. Besides, the detection of metal-chelating peptide is not sensitive enough by spectrophotometry. For the first time, metal chelating peptides were screened in hydrolysates using SPR and a correlation was established between affinity constant determined in SPR and metal chelation capacity determined from UV-visible spectrophotometry.