Positions-Spezifit?t der Peroxidierung von Linol- und Linolens?ure durch Homogenate aus ?pfeln und Birnen

Zusammenfassung Homogenate aus Äpfeln und Birnen wurden mit Linol- und Linolensdure incubiert (25° C, 20 min). Die Hauptprodukte waren Fettsäurehydroperoxyde. Die molaren Anteile, mit denen 13-und 9-Hydroperoxyde gebildet wurden, betrugen bei Äpfeln 82:18 (zu Gunsten des 13-lsomeren) und bei Birnen 10:90 (zu Gunsten des 9-Isomeren). Die Bedeutung der Ergebnisse für die Bildung von Aromastoffen in Äpfeln und Birnen wird diskutiert.

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Positional specificity of the peroxidation of linoleic and linolenic acid by homogenates from apples and pears

Summary Homogenates of apples and pears were incubated (25° C, 20 min), with linoleic and linolenic acid. The major products were fatty acid hydroperoxides. The ratio of 13- to 9-hydroperoxides were at least 82:18 in favour of the 13-isomer for apples and 10:90 in favour of the 9-isomer for pears. The significance of the results for the formation of flavour compounds in apples and pears is discussed.

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Wir danken der Deutschen Forschungsgemeinschaft für die finanzielle Unterstützung der Arbeit     

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/olfacto-metry 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.     

Microfacet Model Regularization for Robust Light Transport

Today, Monte Carlo light transport algorithms are used in many applications to render realistic images. Depending on the complexity of the used methods, several light effects can or cannot be found by the sampling process. Especially, specular and smooth glossy surfaces often lead to high noise and missing light effects. Path space regularization provides a solution, improving any sampling algorithm, by modifying the material evaluation code. Previously, Kaplanyan and Dachsbacher [KD13] introduced the concept for pure specular interactions. We extend this idea to the commonly used microfacet models by manipulating the roughness parameter prior to the evaluation. We also show that this kind of regularization requires a change in the MIS weight computation and provide the solution. Finally, we propose two heuristics to adaptively reduce the introduced bias. Using our method, many complex light effects are reproduced and the fidelity of smooth objects is increased. Additionally, if a path was sampleable before, the variance is partially reduced.     

XAD Resins for Increased Rebeccamycin Productivity in Cultivations of Lentzea aerocolonigenes

Lentzea aerocolonigenes produces the antitumor antibiotic rebeccamycin. For a medical application maximized titers and appropriate downstream processing are necessary. The addition of the adsorbents XAD 4, XAD 17 HP, and XAD 16 N was investigated for increased productivity and in situ product recovery. An increase in product titer was observed for XAD 7 HP and XAD 16 N. A combination of these particles with glass beads led to a further increase. Moreover, rebeccamycin can be adsorbed to these particles which facilitate the extraction since the liquid phase can be dispensed with.     

Comparative evaluation of potent odorants of boiled beef by aroma extract dilution and concentration analysis

 After boiling, beef was extracted with dichloromethane, and the volatile fraction including the solvent was distilled from the non-volatile material. The distillate was divided into two portions; one-half was subjected to aroma extract dilution analysis (AEDA), and the other to aroma extract concentration analysis (AECA). In the latter case, the AECA was accompanied by a series of gas chromatography-olfactometry (GCO) analyses, whereas in the former (i.e. AEDA) the extract was first concentrated to a small volume and then diluted stepwise for GCO analysis. Both screening procedures confirmed the presence of 32 odorants which were all identified after a 250-fold concentration of the extracts. However, the ranking of the compounds in order of odour potency was different due to losses of the odorants in AEDA. 2-Furfurylthiol and 4-hydroxy-2,5-dimethyl-3(2H)-furanone followed by 2-methyl-3-furanthiol and a group containing 3-mercapto-2-pentanone, 1-octen-3-one and (E)-2-non-enal were indicated by AECA to be the most potent odorants of boiled beef. Received: 15 March 1996     

Furan fatty acids in butter and butter oil

Summary Nine furan fatty acids (F-acids), among which 12,15-epoxy-13,14-dimethyleicosa-12,14-dienoic acid and 10,13-epoxy-11,12-dimethyloctadeca-10,12-dienoic acid predominated, were detected in butter and butter oil. The total amount of the F-acids in four butter samples varied between 116 and 476 mg/kg.

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Furanfettsäuren in Butter und Butterschmalz

Zusammensetzung Neun Furanfettsäuren (F-Säuren), unter denen die 12, 15-Epoxy-13,14-dimethyleicosa-12, 14-diensäure und die 10,13-Epoxy-11,12-dimethyloctadeca-10,12-diensäure dominierten, wurden in Butter und Butterschmalz nachgewiesen. In vier Butterproben variierte der Gehalt der F-Säuren zwischen 116 und 476 mg/kg.

     

Changes in glutathione content (reduced and oxidised form) and the effect of ascorbic acid and potassium bromate on glutathione oxidation during dough mixing

During dough mixing, reduced glutathione (GSH) is rapidly oxidised to the disulphide without change in the total glutathione content. The flour improvers potassium bromate and dehydroascorbic acid enhance the oxidation rate of GSH. The intensity of the acceleration caused by various diastereomeric ascorbic acids parallels the improvement of loaf volume, found by Maltha in baking experiments. The data support the assumption that oxidation of GSH by the improvers competes with a SH/SS-interchange reaction of GSH with the gluten proteins.     

Enzymatic oxydation of linoleic acid: Formation of bittertasting fatty acids

Summary Linoleic acid was oxidized with a protein fraction from soya beans (25°C; 2 h), in which lipoxygenase and peroxydase activities occurred. The fatty acids formed were isolated and, after emulsification with a sugar ester, were evaluated for bitter taste. The main components of the bitter-tasting fraction was a mixture of 9.12.13-trihydroxyoctadec-10- and 9.10.13-trihydroxyoctadec-11-enoic acids. The taste threshold lies in the range 0.6–0.9 mol/ml. Two further trihydroxy-acids and two oxodihydroxy-acids were also identified in the bitter-tasting fraction.

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Enzymatische Oxydation von Linolsäure: Bildung von Fettsäuren mit Bittergeschmack

Zusammenfassung Linolsäure wurde mit einer Proteinfraktion aus Sojabohnen oxydiert (25°C; 2 Std), in der Lipoxygenase- und Peroxydaseaktivitäten vorkamen. Die gebildeten Fettsäuren wurden isoliert und nach Emulgierung mit einem Zuckerester auf Bittergeschmack verkostet. Hauptkomponente der bitter schmeckenden Fraktion war ein Gemisch aus der 9,12,13-Trihydroxyoctadec-10- und der 9,10,13-Trihydroxyoctadec-11-ensäure. Die Geschmacksschwelle liegt im Bereich 0,6–0,9 mol/ml. Zwei weitere Trihydroxysäuren und zwei Ketodihydroxysäuren wurden außerdem in der bitter schmeckenden Fraktion identifiziert.

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We are grateful to the Deutsche Forschungsgemeinschaft for supporting this work     

Primary odorants of chicken broth

Summary Aroma extract dilution analysis (AEDA) of the volatiles obtained by the simultaneous distillation/extraction of a chicken broth resulted in 16 primary odour compounds with FD factor values between 64 and 2048. Fourteen of these compounds were identified as: 2-methyl-3-furanthiol, 2-furfurylthiol, methional, 2,4,5-trimethylthiazole, nonanal, 2(E)-nonenal, 2-formyl-5-methylthiophene,p-cresol, 2(E),4(E)-nonadienal, 2(E),4(E)-decadienal, 2-undecenal,-ionone, -decalactone and -dodecalactone. The primary odorants of chicken broth were compared with those resulting from the AEDA of broths from cow and ox meat. The major differences were that 2(E),4(E)-decadienal (fatty) and -dodecalactone (tallowy, fruity) prevailed in the chicken broth, whereas the sulphur compounds, bis(2-methyl-3-furyl)disulphide (meat-like-aroma) and methional (aroma like cooked potatoes), predominated in broths prepared from cow and ox meats. The odour thresholds (in air) of important meat aroma compounds are reported.

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Primäre Geruchsstoffe bei Hühnerbrühe Eine vergleichende Untersuchung mit Brühen aus Kuh- und Ochsenfleisch

Zusammenfassung Durch Aromaextraktverdünnungsanalyse (AEVA) der flüchtigen Verbindungen, isoliert durch simultane Destillation/Extraktion aus Hühnerbrühe, wurden 16 primäre Aromastoffe mit FD-Faktoren im Bereich 64 bis 2048 wahrgenommen. Von diesen Verbindungen wurden 14 identifiziert: 2-Methyl-3-furanthiol, 2-Furfurylthiol, Methional, 2,4,5-Trimethylthiazol, Nonanal, 2(E)-Nonenal, 2-Formyl-5-methylthiophen,p-Kresol, 2(E),4(E)-Nonadienal, 2(E),4(E)-Decadienal, 2-Undecenal,-Ionon, -Decalacton, -Dodecalacton. Die primären Geruchsstoffe der Hühnerbrühe wurden mit denen verglichen, die aus einer AEVA von Kuh- und Ochsenfleischbrühe stammten. Hauptunterschiede waren: 2(E),4(E)-Decadienal (fettig) und -Dodecalacton (talgig, fruchtig) überwogen in Hühnerbrühe, während die Schwefelverbindungen Bis(2-methyl-3-furyl)disulfid (fleischartig) und Methional (gekochte Kartoffeln) in den Brühen aus Rindfleisch dominierten. Die Geruchsschwellen (in Luft) wichtiger Fleischaromastoffe wurden bestimmt.

     

Evaluation of potent odorants in roasted beef by aroma extract dilution analysis

Summary Aroma extract dilution analysis of the volatile fraction isolated from roasted beef resulted in 25 odour compounds of which 22 were identified. 2-Acetyl-2-thiazoline, furaneol, guaiacol, 2-ethyl-3,5-dimethylpyrazine and 2,3-diethyl-5-methylpyrazine were detected as the character impact compounds for the roasty, caramel-like, burnt and earthy odour notes. (E)-2-Nonenal, (E,E)-2,4-decadienal and -octalactone originated, at least in part, from the fat used for the roasting the meat.

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Ermittlung intensiver Geruchsstoffe in gebratenem Rindfleisch durch Aromaextrakt-Verdünnungsanalyse

Zusammenfassung Die Aromaextrakt-Verdünnungsanalyse von gekochtem Rindfleisch ergab 25 Geruchsstoffe, von denen 22 identifiziert wurden. Die röstigen, caramelartigen, brenzlig und erdigen Geruchsnoten im Aroma wurden vom 2-Acetyl-2-thiazolin, Furaneol, Guajacol, 2-Ethyl-3,5-dimethylpyrazin und 2,3-Diethyl-5-methylpyrazin verursacht. (E)-2-Nonenal, (E,E)-2,4-Decadienal und -Octalacton stammten zumindest zum Teil vom zum Braten verwendeten Fett.