Roland Tressl

[Diphenols and caramel compounds in roasted coffees of different varieties. II. (author's transl)].

SummaryEleven diphenols and seven caramel compounds were extracted from roasted coffee with pentane/ether (1 + 1), silylated with BSTFA, characterized, and semiquantified by GC-MS. Seven phenols and five caramel components were identified for the first time in roasted coffee.Robusta coffee contained the highest amounts of phenols and maltol.Arabica showed higher amounts of furaneol (2.5-dimethyl-4-hydroxy-3(2H)-furanone), isomaltol, 5-hydroxymaltol, and 5-hydroxy-5.6-dihydromaltol.ZusammenfassungElf Diphenole and sieben Caramelkomponenten wurden aus entfettetem Röstkaffee durch Extraktion mit Pentan/Äther (1 + 1) isoliert und nach Silylierung mit BSTFA gaschromatographischmassenspektrometrisch charakterisiert and größen-ordnungsmäßig bestimmt. Sieben Phenole und fünf Caramelkomponenten konnten erstmals in Röstkaffee identifiziert warden. Robustakaffee besitzt die größten Mengen an Phenolen and Maltol, während Arabica-kaffee die höchsten Konzentrationen an Furaneol (2,5-Dimethyl-4-hydroxy-3(2H)-furanen), Isomaltol, 5-Hydroxymaltol and 5-Hydroxy-5,6-dihydro-maltol aufweist.

[Volatile phenolic components in beer, smoked beer, and sherry (author's transl)].

SummaryVolatile phenolic compounds of beer, wort, smoked beer, and sherry were enriched, separated, identified, and quantified by means of the methods of column chromatography, gas chromatography, and mass spectrometry. The analyzed foods are significantly varying in the composition and quantity of the phenolic components. Four origins of phenolics in food are shown by these results.ZusammenfassungFlüchtige, phenolische Verbindungen aus Bier, Bierwürze, Rauchbier und Sherry wurden angereichert und mit Hilfe der Methodik Säulenchromatographie — Gaschromatographie — Massenspektrometrie getrennt, identifiziert und quantifiziert. Bedingt durch verschiedene Technologien differieren die untersuchten Lebensmittel deutlich in Art und Menge ihrer phenolischen Inhaltsstoffe. Anhand dieser Ergebnisse werden 4 Quellen für Phenole in Lebensmitteln aufgezeigt.

Purification and characterization of a (R)-2,3-butanediol dehydrogenase from Saccharomyces cerevisiae

A NAD-dependent (R)-2,3-butanediol dehydrogenase (EC 1.1.1.4), selectively catalyzing the oxidation at the (R)-center of 2,3-butanediol irrespective of the absolute configuration of the other carbinol center, was isolated from cell extracts of the yeast Saccharomyces cerevisiae. Purification was achieved by means of streptomycin sulfate treatment, Sephadex G-25 filtration, DEAE-Sepharose CL-6B chromatography, affinity chromatography on Matrex Gel Blue A and Superose 6 prep grade chromatography leading to a 70-fold enrichment of the specific activity with 44% yield. Analysis of chiral products was carried out by gas chromatographic methods via pre-chromatographic derivatization and resolution of corresponding diasteromeric derivatives. The enzyme was capable to reduce irreversibly diacetyl (2,3-butanediol) to (R)-acetoin (3-hydroxy-2-butanone) and in a subsequent reaction reversibly to (R,R)-2,3-butanediol using NADH as coenzyme. 1-Hydroxy-2-ketones and C5-acyloins were also accepted as substrates, whereas the enzyme was inactive towards the reduction of acetone and dihydroxyacetone. The relative molecular mass (Mr) of the enzyme was estimated as 140 000 by means of gel filtration. On SDS-polyacrylamide gel the protein decomposed into 4 (identical) subunits of Mr 35 000. Optimum pH was 6.7 for the reduction of acetoin to 2,3-butanediol and 7.2 for the reverse reaction.

Maillard Reaction of Free and Nucleic Acid-Bound 2-Deoxy-D-ribose and D-Ribose with ω-Amino Acids

The Maillard reaction of free and nucleic acid-bound 2-deoxy-D-ribose and D-ribose with ω-amino acids (4-aminobutyric acid, 6-aminocaproic acid) was investigated under both stringent and mild conditions. Without (with) amines 2-deoxy-D-ribose (D-ribose) displays the strongest browning activity, and DNA is much more reactive than RNA. From stringent reaction between 2-deoxy-D-ribose (or DNA) and methyl 4-aminobutyrate, methyl 4-[2-[(oxopyrrolidinyl)methyl]-1-pyrrolyl]-butyrate (12) was identified by GC/MS and NMR as a new 2-deoxy-D-ribose specific key compound trapped by pyrrolidone formation. Levulinic acid-related N-substituted lactames 13-15 were identified as predominant products from DNA with amino acids, whereas RNA paralleled the reaction with D-ribose. α-Angelica lactone (2), a significant degradation product of DNA, and thiols leads under mild conditions to new addition products (e.g., 17 with glutathione). Probable reaction pathways considering activating effects of the polyphosphate backbone of nucleic acids are discussed.

Gaschromatographisch-massenspektrometrische Untersuchung der im Modellsystem Cystein/Methionin/Furfural unter Röstbedingungen gebildeten Aromastoffe

SummaryThe model-system cysteine/methionine/furfural produced under roasting conditions a complex mixture of compounds which was separated by adsorption chromatography on silica gel, according to the increasing polarity of the components, into six fractions. The fractions were investigated by capillary gas chromatography with and without mass spectrometry. Of the approx. 130 compounds detected, 85 were identified and quantified. Furfural and the reactive degradation products H2S, cysteamine and methylmercaptan, resulting from cysteine and methionine, are important precursors for heterocyclic flavor components. Besides furans, (furan)aldimines, and sulphur-substituted furan derivates, the following compounds are also formed:N-furfurylpyrroles, pyridines, thiazoles, thiazolines, thiazolidines, thiophenes, as well as aliphatic sulphur compounds and cyclic methylene polysulfides. During coffee roasting, furfural is produced as one of the major components of the furans and is essential for the formation of important coffee aroma constituents.ZusammenfassungDas Modellsystem Cystein/Methionin/Furfural lieferte unter Röstbedingungen ein komplexes Reaktionsgemisch, das sich mittels Adsorptionschromatographie auf Kieselgel und Capillar-GC in ca. 130 Komponenten auftrennen ließ, von denen 85 capillargaschromatographisch-massenspektrometrisch charakterisiert wurden. Furfural und die aus Cystein und Methionin resultierenden reaktiven Abbauprodukte H2S, Cysteamin und Methylmercaptan sind wichtige Precursor für heterocyclische Flavorkomponenten. Neben Furanen, (Furan)-aldiminen und schwefelsubstituierten Furanderivaten werden auchN-Furfurylpyrrole, Pyridine, Thiazole, Thiazoline, Thiazolidine, Thiophene sowie aliphatische Schwefelverbindungen und cyclische Methylenpolysulfide gebildet. Beim Kaffeerösten entsteht Furfural als eine der Furanhauptkomponenten und spielt bei der Genese wesentlicher Kaffeearomastoffe eine zentrale Rolle.

Gaschromatographisch-massenspektrometrische Untersuchungen über die Bildung von Phenolen und aromatischen Kohlenwasserstoffen in Lebensmitteln

Phenolic compounds and aromatic hydrocarbons are components in many foods and often typical flavoring substances for example of roasted and smoked products. They are also of toxicological importance. By means of model reactions we have investigated their formation by thermal fragmentation of cinnamic, p-coumaric, ferulic and sinapic acids. The products of these reactions were determined by gas chromatography and identified by mass spectrometry or infrared spectroscopy. Product ratio and mass spectra are given. Barley was roasted in a similar manner, and the components formed were identified. Column chromatography and preparative gas chromatography were used for preliminary separation.SummaryPhenolic compounds and aromatic hydrocarbons are components in many foods and often typical flavoring substances for example of roasted and smoked products. They are also of toxicological importance. By means of model reactions we have investigated their formation by thermal fragmentation of cinnamic, p-coumaric, ferulic and sinapic acids. The products of these reactions were determined by gas chromatography and identified by mass spectrometry or infrared spectroscopy. Product ratio and mass spectra are given. Barley was roasted in a similar manner, and the components formed were identified. Column chromatography and preparative gas chromatography were used for preliminary separation.ZusammenfassungPhenole, Phenoläther und aromatische Kohlenwasserstoffe sind Bestandteile vieler Lebensmittel und oft typische Aromastoffe beispielsweise von Röst- und Räucherprodukten. Sie haben auch toxikologische Bedeutung. In Modellversuchen wurde ihre Bildung durch thermische Fragmentierung von Zimtsäure, p-Cumarsäure, Ferulasäure und Sinapinsäure eingehend untersucht. Die entstandenen Verbindungen wurden gaschromatographisch bestimmt und massenspektrometrisch bzw. infrarotspektroskopisch charakterisiert. Produktverteilung und Massenspektren sind angegeben. In analoger Weise wurde Gerste geröstet und die erzeugten Komponenten identifiziert. Zur Fraktionierung wurden dabei Kieselgel-Säulenchromatographie und präparative Gaschromatographie eingesetzt.

Biodegradation of bis(1-chloro-2-propyl) ether via initial ether scission and subsequent dehalogenation by Rhodococcus sp. strain DTB

Rhodococcus sp. strain DTB (DSM 44534) grows on bis(1-chloro-2-propyl) ether (DDE) as sole source of carbon and energy. The non-chlorinated diisopropyl ether and bis(1-hydroxy-2-propyl) ether, however, did not serve as substrates. In ether degradation experiments with dense cell suspensions, 1-chloro-2-propanol and chloroacetone were formed, which indicated that scission of the ether bond is the first step while dehalogenation of the chlorinated C3-compounds occurs at a later stage of the degradation pathway. Inhibition of ether scission by methimazole suggested that the first step in degradation is catalyzed by a flavin-dependent enzyme activity. The non-chlorinated compounds 1,2-propanediol, hydroxyacetone, lactate, pyruvate, 1-propanol, propanal, and propionate also supported growth, which suggested that the intermediates 1,2-propanediol and hydroxyacetone are converted to pyruvate or to propionate, which can be channeled into the citric acid cycle by a number of routes. Total release of chloride and growth-yield experiments with DDE and non-chlorinated C3-compounds suggested complete biodegradation of the chlorinated ether.

Heat Generated Flavors and Precursors

The essential progress in the chemistry of heat generated flavors and their precursors since 1960 as well as the most important topics in this field are summarized. Starting with J. E. Hodge’s fundamental Maillard reaction scheme, presented first in 1953 and specified in a symposium “The Chemistry and Physiology of Flavors” in 1967, the improvements of the postulated pathways from reducing sugars to flavor compounds, reductones, and melanoidins are described. These improvements are based on the isolation and the chromatographic and spectroscopic characterization of many amino acid specific compounds in foods and Maillard model systems. Their formation could be explained within Hodge’s scheme from different precursors on specific routes, mainly on the basis of labeling experiments using 13C-labeled hexoses, pentoses, and disaccharides.

Transient accumulation of γ-butyrolactone during degradation of bis(4-chloro-n-butyl) ether by diethylether-grown Rhodococcus sp. strain DTB

Rhodococcus sp. strain DTB (DSM 44534) grows aerobically on diethylether as sole source of carbon and energy. Dense cell suspension experiments showed that the induced ether-cleaving enzyme system attacks a broad range of ethers like tetrahydrofuran, phenetole and chlorinated alkylethers including Cα-substituted alkylethers. Identification of metabolites revealed that degradation of the ethers started by an initial attack of the ether bond. Diethylether-grown cells degraded bis(4-chloro-n-butyl) ether via an initial ether scission followed by the transient accumulation of γ-butyrolactone as intermediate at nearly stoichiometric concentrations.

The Peptide-catalyzed Maillard Reaction

The reaction pathways of amino acids and reducing sugars are now fully understood. The focus in the last few years, however, has turned to the reaction of peptides and proteins with reducing sugars. We have investigated the reaction of γ‐aminobutanoic acid, the heptapeptide Nα‐Acetyl‐Lys‐Lys‐β‐Ala‐Lys‐β‐Ala‐Lys‐Gly, and the model protein β‐casein in Maillard reactions with 1‐13C arabinose. Characterization of 13C‐labeled acetic acid and norfuraneol by gas chromatography–mass spectrometry and nuclear magnetic resonance revealed new formation pathways. The results demonstrate significant differences in the labeling pattern of the products depending on the amine used, indicating different formation pathways of acetic acid and norfuraneol.