Co-oxidation of beta-carotene and canthaxanthine by purified lipoxygenases from soya beans (author's transl)]

Isolation and purification of soya bean lipoxygenase (linoleate: O2 oxidoreductase, EC, 1.13.11.12) on Sephadex G-200, DEAE-cellulose and by isolectric focusing yields two isoenzymes of the L- 2 type (optimum pH 6.5) and two of the L-1 type (optimum pH9.0). Different crude extracts from soya beans as well as the purified L-2 isoenzymes exhibit the same capacity for co-oxidation of beta-carotene and canthaxanthine, when the comparison is based upon equal lipoxygenase activities. In contrast to L-2 the alkaline lipoxygenase L-1 is a poor "carotene oxidase".     

Contribution of linoleic acid to the bitter taste of poppy seeds (Papaver somniferum)

In lipids isolated from poppy seeds which tasted "burning-bitter" the off-taste was associated with the free fatty acids fraction. In this fraction linoleic acid predominates, while oxidized fatty acids were among the minor constituents. The taste threshold of linoleic acid emulsified in water with monolinolein lies in the range of 4.0-6.0 mumol/ml. On the basis of its high concentration and relatively low taste threshold we conclude that free linoleic acid contributes significantly to the "burning-bitter" off-taste in poppy seeds.     

Quantification of character-impact odour compounds of roasted beef

Beef was roasted for 7 min in frying pans made of glass (A) or of stainless steel (B). The lower temperature in A yielded a more roasty-sweet flavour and the higher temperature in B a roasty-harsh, more caramellike flavour. Using stable isotope dilution assays the concentration levels of the odour compounds 4-hydroxy-2,5-dimethyl-3(2H)-furanone (I), 2-acetyl-2-thiazoline (II), 2-ethyl-3,5-dimethylpyrazine (III), 2,3-diethyl-5-methylpyrazine (IV), guaiacol (V) and methional (VI) were determined in samples A and B. The data obtained were divided by the corresponding odour thresholds which were evaluated nasally and retronasally. The results indicated that the flavour differences of A and B were preferentially caused by differences in the concentration levels of odorantsI, II, IV, andVI.

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Quantitative Analyse charakteristischer Geruchsstoffe von gebratenem Rindfleisch

Zusammenfassung Rindfleisch wurde 7 min in Pfannen aus Glas (A) und rostfreiem Stahl (B) gebraten. Die niedrigere Temperatur in A führte zu einem stärker röstig-süßen Aroma und die höhere Temperatur in B zu einem röstig-herben, stärker caramelartigen Aroma. Die Konzentrationen der Geruchsstoffe 4-Hydroxy-2,5-dimethyl-3(2H)-furanon (I), 2-Acetyl-2-thiazolin (II), 2-Ethyl-3,5-dimethyl-pyrazin (III), 2,3-Diethyl-5-methylpyrazin (IV), Guajacol (V) und Methional (VI) wurden in den Proben A und B mit Hilfe von Isotopenverdünnungsanalysen bestimmt. Die erhaltenen Werte wurden dividiert durch die entsprechenden nasal und retronasal ermittelten Geruchsschwellen. Die Ergebnisse zeigten, daß die Aromaunterschiede von A und B in erster Linie auf Unterschiede in den Konzentrationen der GeruchsstoffeI,II, IV undVI beruhen.

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Presented in part at the symposium Flavour Precursors, University of Würzburg, Sept. 30th to Oct. 2nd, 1992     

Model Study of Different Antioxidant Properties of α- and γ-Tocopherol in Fats

A model study using 2,2,5,7,8-pentamethyl-6-hydroxychroman (α-COH) and 2,2,7,8-tetramethyl-6-hydroxychroman (γ-COH) as antioxidants, and linoleic acid and its methyl ester (both in bulk phase) as the lipids was performed. After having demonstrated that the antioxidative activities of the model substances did agree with those of the corresponding tocopherols (α-T, γ-T), the stability of α-COH and γ-COH was determined, and the products arising from α-COH, γ-COH, linoleic acid and its methyl ester were identified. α-COH did oxidize to different major products (quinone, trimer) depending on the reaction temperature (37°C and 47°C) and the antioxidant concentration, whereas the products obtained by oxidation of γ-COH (diphenyl ether dimer, biphenyl dimer) did not seem to be affected by differences in the reaction conditions. It was concluded that γ-T was superior to α-T as antioxidant because it appears more stable and, also, being oxidized to compounds which are still effective as antioxidants.     

Quantitative analysis of caffeic and ferulic acids in oatmeal

[¹³C]Caffeic acid and [¹³C]ferulic acid were synthesized and then used as internal standards for the determination of these acids (free and esterified) in oatmeal. A comparative study indicated that 84% of the ferulic acid, but only 32% of the caffeic acid, which is more susceptible to oxidation than the former, could be found by a conventional analytical approach.

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Quantitative Analyse von Kaffee- und Ferulasäure in Hafermehl. Vergleich einer konventionellen Methode mit einem Stable Isotope Dilution Assay

Zusammenfassung [¹³C]-Kaffee- und [¹³C]-Ferulasäure wurden synthetisiert und als interne Standardsubstanzen für die Bestimmung dieser Säuren (frei und verestert) in Hafermehl angewandt. Ein Vergleich ergab, daß von der Ferulasäure 84%, aber von der leichter oxidablen Kaffeesäure nur 32% mit einer konventionellen Methode erfaßt werden.

     

Potent odorants resulting from the peroxidation of lemon oil

Summary The odorants of a lemon oil sample, which was peroxidized for 120 h at room temperature in the presence of light, were analysed by an aroma extract dilution procedure. On the basis of their FD factors carvone,p-methylacetophenone,p-cresol, 4-acetyl-1-methyl-1-cyclohexene and 4 hydroperoxides were identified as the most intense odorants. Changes in the concentrations of neral, geranial, linalool (odorants of the fresh lemon oil), carvone,p-methylacetophenone,p-cresol andp-cymene (dependent on the storage time) were determined and the odour units for these compounds were calculated.

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Intensive Geruchsstoffe aus peroxidiertem Zitronenol

Zusammenfassung Die intensivsten Geruchsstoffe eines Zitronenöls, das 120 h bei Raumtemperatur bestrahlt worden war, wurden identifiziert. Eine Aromastoffverdünnungsanalyse ergab hohe FD-Faktoren bei Carvon,p-Methylacetophenon,p-Kresol, 4-Acetyl-1-methyl-l-cyclohexen und bei vier Limonenhydroperoxiden. Vom Neral, Geranial und Linalool (Geruchsstoffe des frischen Öls) Bowie vom Carvon,p-Methylacetophenon,p-Kresol undp-Cymen wurde die Konzentration in Abhangigkeit von der Lagerzeit bestimmt und der Aromawert berechnet.

     

Dependence of the 12-methyltridecanal concentration in beef on the age of the animal

The content of 12-methyltridecanal (12-MT), which contributes greatly to the characteristic aroma of stewed beef, was determined by a stable isotope dilution assay in meat samples from nine bovine animals of different ages. The results, which were related to the amount of phospholipids (PL), indicate that 12-MT content increases with the age of beef, e. g. from 36 g·g^–1 PL in a 4-monthold calf to 810 g·g^–1 PL in an 8-year-old cow. The increase of 12-MT content in PL per month varied between 8.4 and 10.9 g·g^–1 PL (mean: 9.3 ± 0.78 g·g^–1 PL). Possibly 12-MT content is suitable as an indicator for the estimation of the age of a beef sample.

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Abhängigkeit der 12-Methyltridecanal-Konzentration in Rindfleisch vom Alter des Tieres

Zusammenfassung 12-Methyltridecanal (12-MT), das zum charakteristischen Aroma von geschmortem Rindfleisch wesentlich beiträgt, wurde durch Isotopenverdünnungsanalyse in Proben aus neun Rindern unterschiedlichen Alters bestimmt. Die Ergebnisse, die auf den Phospholipid (PL)-Gehalt bezogen wurden, zeigen, daß das 12-MT mit dem Alter des Rindes ansteigt, z.B. von 36 g·g^–1 PL bei einem 4 Monate alten Kalb auf 810 g·g^–1 PL in einer 8 Jahre alten Kuh. Der Anstieg des 12-MT in den PL pro Monat schwankte zwischen 8,4 und 10,9 g·g^–1 (Mittelwert 9,3 ±0,78 g·g^–1). Möglicherweise ist das 12-MT als Indikator für die Altersbestimmung von Rindfleisch geeignet.