Co-oxidation of carotenes requires one soybean lipoxygenase isoenzyme.

The type II lipoxygenase (optimum pH 6.5) from soybeans was purified and separated into two fractions either by chromatography on DEAE-Sephadex or by isoelectric focusing. In the presence of linoleic acid and oxygen both fractions co-oxidise canthaxanthine or beta-carotene as effectively as a combination of these fractions. Oxygenation of linoleic acid and co-oxidation of canthaxanthine by type II lipoxygenase is stimulated by 13-hydroperoxy-cis-9,trans-11-octadecadienoic acid but not by 13-hydroxy-cis-9,trans-11-octadecadienoic acid or 9-hydroperoxy-trans-10,cis-12-octadecadienoic acid.

A study of oxygen isotope scrambling in the enzymic and non-enzymic oxidation of linoleic acid.

Lipoxygenases-1 and -2 isolated from soybeans were incubated with linoleic acid in the presence of a mixture of 16O2 and 18O2. The formation of 16O/18O-molecules which is indicative for a head-to head reaction of peroxy radicals was determined and compared with that produced during autoxidation of a linoleic acid emulsion in the presence of ferric ions. Lipoxygenase-1 was much less active in scrambling than lipoxygenase-2 which was comparable to that found in the autoxidation reaction.

Photolysis of unsaturated fatty acid hydroperoxides. 4. Fatty acid products from the aerobic decomposition of methyl 13(S)-hydroperoxy-9(Z),11(E)-octadecadienoate dissolved in cyclohexane.

In the presence of oxygen, UV-irradiation of a solution of methyl 13(S)-hydroperoxy-9(Z),11(E)-octadecadienoate (13-HPOD) in cyclohexane leads to a broad pattern of reaction products of which a trihydroxyene, seven epoxyhydroxides, four hydroxydienes, four epoxyhydroperoxides, six oxodienes and an epoxycyclohexylene were identified as the main components. Two oxodienes having a (Z)-double bond adjacent to the carbonyl group and the epoxycyclohexylene are reported for the first time. In contrast to results published recently for the UV-degradation of the 13-HPOD in methanol, the decomposition of the 13-HPOD in cyclohexane results in the formation of the 9-HPOD by a rearrangement of the hydroperoxy group. Consequently the reaction products are formed as mixtures of positional isomers. The reaction pathways leading to the identified compounds are discussed.

Potent odorants of raw Arabica coffee. Their changes during roasting.

Aroma extract dilution analysis of raw Arabica coffee revealed 3-isobutyl-2-methoxypyrazine (I), 2-methoxy-3,5-dimethylpyrazine (II), ethyl 2-methylbutyrate (III), ethyl 3-methylbutyrate (IV), and 3-isopropyl-2-methoxypyrazine (V) as potent odorants. The highest odor activity value was found for I followed by II, IV, and V. It was concluded that I was responsible for the characteristic, peasy odor note of raw coffee. Twelve odorants occurring in raw coffee and (E)-beta-damascenone were also quantified after roasting. The concentration of I did not change, whereas methional, 3-hydroxy-4, 5-dimethyl-2(5H)-furanone, vanillin, (E)-beta-damascenone, and 4-vinyl- and 4-ethylguaiacol increased strongly during the roasting process.

Study of the effect of DATEM. 1. Influence of fatty acid chain length on rheology and baking.

To answer the question of which fatty acid residue is the most effective, diacetyltartaric esters of monoglycerides (DATEMs) with fatty acids of chain lengths 6:0-20:0 were synthesized. The activity of synthesized DATEMs and commercial DATEM products was studied by means of rheological methods and a microscale baking test with 10 g of flour. Variation of the acyl residue from 6:0 to 22:0 showed that stearic acid (18:0) had the best effect on the baking activity of DATEM (loaf volume increased by 62%). DATEMs containing unsaturated fatty acids (18:1, 18:2) or DATEMs produced from diacylglycerols instead of monoacylglycerols showed a slight increase of the loaf volumes. A slight effect of DATEM on the rheology of dough was observed. However, much greater was the effect on the gluten isolated from doughs prepared with DATEM. The resistance of gluten to extension was increased after the addition of increasing amounts of DATEM (0.1-0.5%). Within the series of DATEMs derived from the homologous series of monoacylglycerols the product based on glycerol monostearate (18:0) showed a maximum increase of the gluten resistance.

Sensory study on the character impact odorants of roasted arabica coffee.

The potent odorants were quantified in a sample of roasted Arabica coffee. On the basis of the results, 27 odorants were dissolved in an oil/water mixture. The flavor profile of the model obtained was very close to that of the real sample. In duo and triangle tests, the model was compared with models missing one or more odorants. These experiments indicated that 2-furfurylthiol, 4-vinylguaiacol, several alkyl pyrazines, furanones, acetaldehyde, propanal, methylpropanal, and 2- and 3-methylbutanal had the greatest impact on the coffee flavor.

Occurrence of 12-methyltridecanal in microorganisms and physiological samples isolated from beef.

12-Methyltridecanal (MT) smelling tallowy, beef-like was formed from plasmalogens when beef was boiled. To clarify the origin of MT, its concentration was determined by a stable isotope dilution assay in bacteria and protozoa isolated from the rumen of bovine animals as well as in the plasma, erythrocytes, and other physiological samples. The highest amounts of MT were found in bacteria followed by protozoa. The MT content of the erythrocytes was small. The results support the hypothesis that microorganisms are the main source of MT of which a small amount is resorbed by the animal and transported to the muscular tissue where MT is incorporated into plasmalogens.

Development of a stable isotope dilution assay for the quantification of 5-methyl-(E)-2-hepten-4-one: application to hazelnut oils and hazelnuts.

A stable isotope dilution assay was developed for the quantitation of the hazelnut odorant 5-methyl-(E)-2-hepten-4-one by mass chromatography using synthesized [(2)H](2)-5-methyl-(E)-2-hepten-4-one as the internal standard. Application of the method on two batches of commercial hazelnut oils, processed from either roasted or unroasted nuts, revealed 6.4 microg 5-methyl-(E)-2-hepten-4-one per kg of unroasted oil whereas 315.8 microg per kg was determined in the roasted nut oil. The about 50-fold higher amount of 5-methyl-(E)-2-hepten-4-one in roasted hazelnut oil suggested the necessity of a thermal treatment to generate the flavor compound. Pan frying of raw hazelnuts (9 to 15 min) or boiling of the crushed nut material for 1 h in water led to an increase of 5-methyl-(E)-2-hepten-4-one by factors of 600 and 800, respectively, thereby corroborating that the major part of the nut flavorant is formed during heat treatment from a yet unknown precursor in hazelnuts.

Autoxidation of phenyl linoleate and phenyl oleate: HPLC analysis of the major and minor monohydroperoxides as phenyl hydroxystearates.

Phenyl linoleate was oxidized under different conditions. The monohydroperoxide products were isolated and subsequently hydrogenated. The isomers of phenyl hydroxysterate obtained were separated by high pressure liquid chromatography. On the basis of cochromatography with reference materials and mass spectroscopy, it was shown that the mixture was composed mainly (96%) of phenyl 9-hydroxy- and phenyl 13-hydroxysterates (9- and 13-HOPh) with 8-, 10-, 12- and 14-HOPh as minor compounds (4%). In the minor fraction, the 8- and 14-HOPh predominated in comparison to the 10- and 12-HOPh. The presence of α-tocopherol in the autoxidation experiment changed the proportion of the phenyl hydroxystearate isomers: the proportion of the 9- and 13-HOPh increased and those of the 8- and 14-HOPh decreased. After addition of 0.05% or higher concentrations of α-tocopherol, the minor fraction comprised approximately equal amounts of 8-, 10-, 12- and 14-HOPh. Autoxidation of phenyl oleate followed by hydrogenation of the monohydroperoxides resulted in the formation of a mixture of phenyl hydroxystearates containing approximately equal amounts of 8-, 9-, 10- and 11-HOPh.

Enzymic oxidation of linolenic acid to 1,Z-5-octadien-3-ol, Z-2,Z-5-octadien-1-ol and 10-oxo-E-8-decenoic acid by a protein fraction from mushrooms (Psalliota bispora).

The pathway for the oxidative cleavage of linolenic acid was investigated using a protein fraction from mushrooms (Psalliota bispora) as the enzyme source. Incubation of the protein fraction with linolenic acid resulted in 1,Z-5-octadien-3(R)-ol and Z-2,Z-5-octadien-1-ol (in a 3∶2 ratio) and 10-oxo-E-8-decenoic acid (10-ODA). Experiments with molecular oxygen-18 indicated that the oxygen in the hydroxy group of both octadienols originates from the gaseous phase and not from water. The protein fraction was incubated with the individual 9-, 10-, 12-, 13-, 15- and 16-hydroperoxide isomers of linolenic acid. Only the 10-hydroperoxy-E-8,Z-12,Z-15-octadecatrienoic acid (10-HPOT) served as substrate, and was cleaved into the two octadienols and the 10-ODA. This result suggests that in the oxidation of linolenic acid by the mushroom fraction the 10-HPOT is an intermediate cleaved by a hydroperoxide lyase into the octadienols and the 10-ODA. Model experiments in which the methyl esters of both 10-hydroperoxy-E-8,Z-12-octadecadienoic acid (10-HPOD) and 10-HPOT were treated with the Lewis acid BF3 yielded only various C9 compounds. It was therefore concluded that the reactions of the mushroom hydroperoxide lyase cannot be explained by the heterolytic rearrangement mechanism, which was proposed for the corresponding plant enzyme. ß-Scission of the 10-HPOD and the 10-HPOT explains the reactions of the mushroom hydroperoxide lyase and is discussed in detail.

Apparatus for the quantitative analysis of the aroma of french bread and its loss during storage.

Based on the principles of static and dynamic headspace sampling, an apparatus was developed for the determination of the release of potent odorants from two types of baguette (industrial process or "intensifée" and traditional or "artisanal") differing in their odor profiles. We applied this apparatus to get an insight into the aroma changes of freshly baked French bread, which develops a stale off-flavor within four hours after baking. Model mixtures containing the odorants in the concentrations found by the headspace analysis were evaluated using the apparatus as an olfactometer. By comparing the odor profiles of the models with those of the baguettes, the quantitative data were confirmed. The results indicate that losses of methylpropanal, 2- and 3-methylbutanal and, on the other hand, an increase of hexanal and (E)-2-nonenal led to a stale off-flavor. Furthermore it was suggested that this apparatus is also suitable for precise flavor release studies of other foods.

[Breakdown of linoeic acid hydroperoxydes. Formation of volatile carbonyl compounds (author's transl)]. / Abbau von Linolsäurehydroperoxyden zu flüchtigen Monocarbonylvervindungen

Linoleic acid hydroperoxydes (LOOH) containing 13-hydroperoxyoctadeca-9,11-(75%) and 9-hydroperoxyoctadeca-10,12-dienoic acid (25%) were emulsified at pH 6.5. After addition of hemoglobin, ferrous ions, ferric ions, cysteine or ascorbic acid the emulsions were stored 19 hours at 22 degrees C. The decrease in the diene and peroxyde concentrations and the formation of volatile carbonyl compounds were analysed. Ferrous ions and ascorbic acid were the strongest producers of volatile carbonyl compounds. In the presence of 10(-3) Mol ascorbic acid 6 mumol volatile aldehydes arise from 75 mumol LOOH. Hexanal (70 mol-%) was the main component of the aldehyde fraction. For plant foodstuffs the significance of the reaction of fatty acids hydroperoxydes with ascorbic acid for the formation of flavour substances is discussed.

Flavour of coffee. A review.

The concept of flavour analysis developed in our laboratory during the last decade to evaluate the key odorants of foods and beverages, is demonstrated in a review on coffee flavour. The results obtained by aroma extract dilution analysis (AEDA), gas chromatography/olfactometry of headspace samples and quantitation of potent odorants using corresponding stable isotopomers as internal standards are discussed. Finally, some sensory experiments performed on the basis of data assessed by instrumental analyses of roasted coffee samples are reported.