Quantitative assessment of enzymatic processes applied to flavour and fragrance standard compounds using gas chromatography with flame ionisation detection.

The performance of different enzymes towards the bioprocessing of aroma-related compounds was investigated and a strategy based on GC-FID analysis was developed to facilitate assessment of the stages of characterisation, screening and optimisation, including chiral ratio determination. Characterisation included activity assays (UV-Vis and GC-FID), protein quantification (NanoDrop spectrophotometry) and molar mass estimation (SDS-PAGE electrophoresis). Screening experiments assessed different enzymes, substrates, solvents, acyl donors or mediators. Aroma-related substrates comprised terpene and phenolic compounds. The enzymes tested included the lipases CALA (Sigma-Aldrich), NZ-435, LZ-TLIM, NC-ADL, LZ-CALBL and the laccases NZ-51003 and DL-IIS (all from Novozymes). Among those, NZ-435 and NZ-51003 had the highest activities in the characterisation stage and, along with CALA, achieved conversions above 70% for citronellol (lipases) or 50% for eugenol (laccases) at the screening stage. The lipases had preference for the primary alcohol and laccases for phenolic compounds, among the tested substrates. The transesterification reaction between the lipase CALA and the standards mixture (citronellol, menthol, linalool) was used to demonstrate the optimisation stage, where the best levels of temperature, enzyme and acyl donor concentrations were investigated. Optimum conditions were found to be 37-40 °C, 3-4 mg/mL of enzyme and 58-60% (v/v) vinyl acetate. Additional confirmation experiments using the same terpene standards mixture and citronella oil sample, gave a conversion of > 95% for citronellol after 1 h (for both, standards mixture and sample), and 20% or 74% for menthol after 1 h or 24 h, respectively. None of the tested enzymes demonstrated significant enantioselectivity under the tested conditions. The GC-FID approach demonstrated here was suitable to determine the reaction profiles and chiral ratio variations for biocatalysed reactions with aroma compounds in low complexity samples. Advanced separations will be applied to more complex samples in the future.

A capillary electrophoretic-mass spectrometric method for the assessment of octreotide stability under stress conditions.

A capillary zone electrophoretic-electrospray ion trap mass spectrometric method has been developed to assess the stability and pathways of degradation of the cancer therapeutic octapeptide, octreotide. As a somatostatin analogue, octreotide contains a single disulphide bond linking Cys(2)-Cys(7) with the structure of NH2-D-Phe-[Formula: see text]-Thr-OH. Resolution of octreotide from its degradation products was achieved using a capillary zone electrophoretic method with bare fused silica capillaries, a 10mM ammonium formate buffer, pH 3.20, at 25 °C and an applied voltage of 25 kV. An ion trap low energy collision induced dissociation procedure was applied for the characterization of the chemical structures of the degradation products derived from an acidic, alkaline, neutral and thermal solution treatment of octreotide. The results so obtained indicated that linear octreotide degradation products were formed under acidic and alkaline conditions, due to the hydrolysis of a ring amide bond and a hitherto unknown desulfurization of the Cys-Cys disulfide bond, respectively. Degradation under neutral conditions occurred via cleavage of the exocyclic N-((2R,3R)-1,3-dihydroxybutan-2-yl) amide bond which also preceded the ring amide hydrolysis under acidic conditions. The developed method was further successfully applied to assess the kinetics of these octreotide degradations. Overall, this method is suitable for the rapid and precise assessment of the stability and quality control of octreotide as a synthetic peptide-based pharmaceutical product, and has led to the discovery of a new Cys-Cys disulfide degradation pathway.

Thermodynamic assessment of the stability of thrombin receptor antagonistic peptides in hydrophobic environments.

In this paper, a general procedure is described to determine thermodynamic parameters associated with the interaction of thrombin receptor antagonistic peptides (TRAPs) with immobilized nonpolar ligands. The results show that these interactions were associated with nonlinear van't Hoff dependencies over a wide temperature range. Moreover, changes in relevant thermodynamic parameters, namely the changes in Gibbs free energy of interaction, DeltaG(0)assoc, enthalpy of interaction, DeltaH(0)assoc, entropy of interaction, DeltaS(0)assoc, and heat capacity, DeltaC(0)p, have been related to the structural properties of these TRAP analogs. The implications of these investigations for the design of thrombin receptor agonists/antagonists with structures stabilized by intramolecular hydrophobic interactions are discussed.