Browsing by Subject "Phenols"

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Characterization of the aroma profile of food smoke at controllable pyrolysis temperatures
(2023) Rigling, Marina; Höckmeier, Laura; Leible, Malte; Herrmann, Kurt; Gibis, Monika; Weiss, Jochen; Zhang, Yanyan
Smoking is used to give food its typical aroma and to obtain the desired techno-functional properties of the product. To gain a deeper knowledge of the whole process of food smoking, a controllable smoking process was developed, and the influence of wood pyrolysis temperature (150–900 °C) on the volatile compounds in the smoking chamber atmosphere was investigated. The aroma profile of smoke was decoded by headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). Subsequently, the correlations in the most important substance classes, as well as in individual target components, were investigated by the Pearson test. Phenols and lactones showed an increase over the entire applied temperature range (rT = 0.94 and rT = 0.90), whereas furans and carbonyls showed no strict temperature dependence (rT < 0.6). Investigations on single aroma compounds showed that not all compounds of one substance class showed the same behavior, e.g., guaiacol showed no significant increase over the applied pyrolysis temperature, whereas syringol and hydoxyacetone showed a plateau after 450 °C, and phenol and cyclotene increased linear over the applied temperature range. These findings will help to better understand the production of aroma-active compounds during smoke generation in order to meet consumers preferences.
Selektive und effiziente Laccase-katalysierte oxidative Phenolkupplungen
(2012) Constantin, Mihaela-Anca; Beifuss, Uwe
The oxidative phenolic coupling is one of the fundamental reactions of organic chemistry. In contrast to its major role in the biosynthesis of numerous natural compounds the oxidative phenolic coupling is only of little importance in organic synthesis so far. This is due to its frequent lack of regio- and stereoselectivity. Laccases are oxidases which can be employed, amongst others, for the catalysis of oxidative phenolic couplings using O2 as the oxidant. This study highlights three examples which clearly demonstrate that laccases can be used as catalysts for regio- and stereoselective oxidative couplings of phenolic compounds. The first example deals with the laccase-catalyzed oxidative dimerization of (E)-2-propenylsesamol to carpanone (a). The oxidative cyclization starts with a phenolic oxidation, which is followed by a radical coupling and an intramolecular hetero-Diels-Alder reaction. Experiments with laccases and a number of other catalysts indicate that the diastereoselectivity of the carpanone formation doesn´t depend on the nature of the catalyst but on the double bond geometry of the substrate. With (E)-2-propenylsesamol as the substrate, a 9:1-mixture of carpanone (a) and its diastereoisomer c was formed, irrespective of the catalyst used. When (Z)-2-propenylsesamol was used as the substrate, the formation of a 5:1:4-mixture of three diastereoisomers, i.e. a, c and d, was observed. When the oxidation of (E)-2-propenylsesamol with O2 as the oxidant was run in the absence of any catalyst the diastereoisomeric benzopyrans a and b were obtained in a 3:2-ratio. From a mechanistic point of view, this reaction proceeds as a Domino oxidation/intermolecular hetero-Diels-Alder reaction. The second example selected was the laccase-catalyzed oxidative coupling of sesamol, a naturally occurring phenolic antioxidant. Here, a so far unknown trimer was formed as the main product in good yield. Experiments with different catalysts indicated that the course of the oxidative coupling of sesamol depends strongly on the catalyst chosen. Finally, the laccase-catalyzed phenolic coupling of di- and trisubstituted vanillidene derivatives with O2 as the oxidant was studied. The dimerization of (E)-ferulic acid proceeded as a 8,8?-coupling with formation of a dilactone. When the disubstituted vanillidene derivatives were reacted, the diastereoselective formation of the racemic dihydrobenzo[b]furans which can be understood as the products of a 5,8?-coupling mode were formed. In contrast to the disubstituted vanillidene derivatives, the laccase-catalyzed reaction of the trisubstituted vanillidene derivatives exclusively yielded biphenyls as the result of a 5,5?-coupling.