Remy Liardon

Determination of d-amino acids by deuterium labelling and selected ion monitoring

Abstract A method for the accurate determination of d -amino acids in protein/peptide samples has been developed. This method differentiates d -isomers formed during protein acid hydrolysis from the initial contribution of the sample. To this effect, the hydrolysis is carried out in deuterated hydrochloric acid. Any molecule that is inverted during this step becomes automatically labelled with deuterium. Amino acids are then separated by gas chromatography as N(O,S)-trifluoroacetyl-O-isopropyl esters on a chiral stationary phase and detected by mass spectrometry in selected ion monitoring mode. At present, twelve protein amino acids, including seven essential ones, are monitored in a two-run procedure. This technique allows the determination of the d / l ratio down to 0.1%. Based on this method, the inversion rate constants of fifteen amino acids have been determined under acid hydrolysis conditions (110°C, 6 N 2 HCl). Preliminary data are presented on the racemization induced in protein samples heated in the solid state in the presence of low amounts of water.

Representativeness of coffee aroma extracts : a comparison of different extraction methods

Analyses for the investigation of aroma components are routinely performed on coffee aromatic extracts. Various extraction methods exist. Ideally, the extraction method used should provide an extract with sensory characteristics as close as possible to the complete product. This is particularly relevant in the case of coffee, as no single key compound has been demonstrated as being responsible for the typical flavour of roasted and ground coffee. The purpose of this study was to compare various methods to see which provided an aromatic extract most representative of coffee. Five different extraction methods were compared: supercritical fluid extraction with carbon dioxide, simultaneous distillation extraction, oil recovery under pressure and vacuum steam-stripping with water or with organic solvent. In addition, Arabica Colombia coffee was used at three different roasting levels, i.e. green coffee as well as the same coffee light-roasted and medium roasted. Sensory testing of the extracts showed that vacuum steam-stripping with water provided the most representative aroma extract, for all three coffees.

The diffusion kinetics of carbon dioxide in fresh roasted and ground coffee

Abstract Carbon dioxide is produced as a result of many reactions that take place during roasting of coffee. Although some carbon dioxide is released during roasting and upon grinding, some is trapped and slowly released creating a packaging problem. Either vacuum packaging to prevent a billowing of the package or special film to release CO 2 from inside the package are required. In addition, the coffee is usually tempered in order to maximize release of CO 2 before packaging. In this research, the diffusion kinetics of carbon dioxide release from fresh roasted and ground coffee during tempering were determined. The CO 2 degassing results fit a series expansion of Fick’s law for unsteady state diffusion using either one or two effective diffusivities based on an analysis of transport mechanisms. The calculated effective diffusivity was between 0.5 and 10×10 −13 m 2 /s. It appears that pressure flow and Knudsen diffusion take place and are important during tempering.

Volatile Components of Fermented Soya Hydrolysate

ZusammenfassungZur Herstellung von fermentiertem Soja Hydrolysat (FSH), oder Sojasauce, wurden Sojabohnen mit geröstetem oder ungeröstetem Mehl gemischt. Diese Mischung wurde einer Fermentation in trockener Form mitAspergillus oryzae unterzogen (Zwischenprodukt: fermentierte Soja Cake FSC), darauf erfolgte eine weitere Fermentation in alkoholischem Milieu mitSaccharomyces rouxii.Die basischen, flüchtigen Komponenten vom Zwischenprodukt und vom Endprodukt wurden isoliert, anschließend qualitativ und quantiativ analysiert. Die identifizierten Komponenten sind Alkylpyrazine, Alkylpyridine und verschiedene Amide.Der Vergleich der Zusammensetzung von FSH und FSC zeigte, daß die meisten basischen Komponenten während der trockenen Fermentation durch den Stoff wechsel der Schimmelpilze gebildet werden; der nicht enzymatische Bräunungsprozeß, welcher während der FSH Reifung stattfand, lieferte einen wesentlich geringeren Anteil.Insgesamt wurde in FSH weniger und kleinere Mengen von basischen, flüchtigen Substanzen gefunden als im entsprechenden FSC Produkt.SummarySoya beans mixed with non-roasted or roasted flour were submitted first to a solid fermentation withAspergillus oryzae, then to an alcoholic fermentation withSaccaromyces rouxii, to prepare samples of fermented soya hydrolysate (FSH), or soya sauce. Basic volatile components were isolated from the final products and from the intermediate fermented soya cakes (FSC), and determined qualitatively and quantitatively. The identified components consisted in alkylpyrazines, alkylpyridines, and various amides.The comparison of FSH und FSC composition revealed that most of the basic components were formed during the solid fermentation by the metabolic activity of the mould, rather than by the non-enzymic browning processes taking place during FSH maturation. Moreover, basic volatiles were found in smaller numbers and amounts in FSH than in the corresponding FSC.