Recognition of volatile compounds as markers in geographical discrimination of Spanish extra virgin olive oils by chemometric analysis of non-specific chromatography volatile profiles

Chromatographic profiles obtained by headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography (GC) were processed as continuous and non-specific signals through multivariate analysis techniques in order to select and identify the most discriminate volatile marker compounds related to the geographical origin of extra virgin olive oils. The blind analysis of the chromatographic profiles was carried out on several steps including preliminary mathematical treatments, explorative analysis, feature selection and classification. The results obtained through the application of stepwise linear discriminant analysis (SLDA) method revealed a perfect discrimination between the different Spanish geographical regions considered (La Rioja, Andalusia and Catalonia). The assignment success rate was 100% in both classification and prediction by using cross validation procedure. In addition, it must be noted that the proposed strategy was able to verify the geographical origin of the samples involving only a reduced number of discriminate retention times selected by the stepwise procedure. This fact emphasizes the quality of the accurate results obtained and encourages the feasibility of similar procedures in olive oil quality and traceability studies. Finally, volatile compounds corresponding to the predictors retained were identified by gas chromatography-mass spectrometry (GC-MS) for a chemical interpretation of their importance in quality virgin olive oils.     

Industrial case study: Evaluation of a mixed-mode resin for selective capture of a human growth factor recombinantly expressed in E. coli

Mixed-mode chromatography resins are gaining popularity as effective purification tools for challenging feedstocks. This study presents the development of an industrial application to selectively capture recombinant human vascular endothelial growth factor (rhVEGF) on Capto MMC from an alkaline feedstock. Capto MMC resin contains a ligand that has the potential to participate in ionic, hydrophobic, and hydrogen boding interactions with proteins and is coupled to a highly cross-linked agarose bead matrix. VEGF is a key growth factor involved in angiogenesis and has therapeutic applications for wound healing. In this process, it is expressed in Escherichia coli as inclusion bodies. Solids are harvested from the cell lysate, and the rhVEGF is solubilized and refolded at pH 9.8 in the presence of urea and redox reagents. The unique mixed-mode characteristics of Capto MMC enabled capture of this basic protein with minimal load conditioning and delivered a concentrated pool for downstream processing with >95% yields while reducing host cell protein content to <1.2%. This study explores the impact of loading conditions and residence time on the dynamic binding capacity as well as the development of elution conditions for optimal purification performance. After evaluating various elution buffers, l-arginine HCl was shown to be an effective eluting agent for rhVEGF desorption from the Capto MMC mixed-mode resin since it successfully disrupted the multiple interactions between the resin and rhVEGF. The lab scale effort produced a robust chromatography step that was successfully implemented at commercial manufacturing scale.     

Modeling of tracer diffusion in liquids when solute–solvent interactions are present

The linear solvation energy relationship (LSER) model is employed to correlate the tracer diffusion coefficients of 550 binary systems at 298.15 K. Among the selected solutes and solvents there exist apolar, polar and hydrogen-bonding substances that can interact with themselves (solvent polymerization) or with the other compound (solute–solvent complexes formation). The results of the proposed formulas are compared with those of other predictive equations.     

Similarity classes of3 × 3 matrices over a discrete valuation ring

Let Q be a complete discrete valuation ring. Let Π be a prime element in Q. Write P = ΠQ. For n = 1,2,…, letQ_n be the factor ring Q | Pⁿ. Let G = G1₃(Q_n. Denote by M?_n the G-module of 3 × 3 matrices over Q_n modulo scalar matrices. Canonical forms are found for every element in M?_n, and it is shown that there exist five sets of similarity classes. Some results about the general case of NxN matrices over Q also are proved.     

Numerical continuation of degenerate homoclinic orbits in planar systems

In this paper we develop numerical algorithms for the continuationof degenerate homoclinic connections in planar systems. We considerthe case where the equilibrium point has zero trace and twocases of higher-order degeneracies. The method we propose isable to continue homoclinic connections of order up to codimension-four.Application of the algorithm to four examples supports its validityand demonstrates its usefulness.