Browsing by Subject "Laccase"

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Comparison of binding properties of a laccase-treated pea protein-sugar beet pectin mixture with methylcellulose in a bacon-type meat analogue
(2022) Moll, Pascal; Salminen, Hanna; Stadtmueller, Lucie; Schmitt, Christophe; Weiss, Jochen
A bacon-type meat analogue consists of different structural layers, such as textured protein and a fat mimetic. To obtain a coherent and appealing product, a suitable binder must glue those elements together. A mixture based on pea protein and sugar beet pectin (r = 2:1, 25% w/w solids, pH 6) with and without laccase addition and a methylcellulose hydrogel (6% w/w) serving as benchmark were applied as binder between textured protein and a fat mimetic. A tensile strength test, during which the layers were torn apart, was performed to measure the binding ability. The pea protein–sugar beet pectin mixture without laccase was viscoelastic and had medium and low binding strength at 25 °C (F ≤ 3.5 N) and 70 °C (F ≈ 1.0 N), respectively. The addition of laccase solidified the mixture and increased binding strength at 25 °C (F ≥ 4.0 N) and 70 °C (F ≈ 2.0 N), due to covalent bonds within the binder and between the binder and the textured protein or the fat mimetic layers. Generally, the binding strength was higher when two textured protein layers were glued together. The binding properties of methylcellulose hydrogel was low (F ≤ 2.0 N), except when two fat mimetic layers were bound due to hydrophobic interactions becoming dominant. The investigated mixed pectin–pea protein system is able serve as a clean-label binder in bacon-type meat analogues, and the application in other products seems promising.
Laccase-katalysierte Dominoreaktionen von Brenzcatechinen und Hydrochinonen mit 1,3-Dicarbonylverbindungen
(2012) Hajdok, Szilvia; Beifuss, Uwe
In the present work novel domino reactions have been described which are based on the laccase-catalyzed oxidation of catechols and hydroquinones to the corresponding o- and p-quinones and their subsequent reactions with 1,3-dicarbonyl compounds. In the first part of this thesis an efficient approach to 3,4-dihydro-7,8-dihydroxy-2H-dibenzofuran-1-ones has been developed. The method includes a laccase-initiated domino reaction between cyclohexane-1,3-diones and catechols using air as an oxidant. The reactions can be carried out under mild reaction conditions without using toxic reagents. The products were obtained in yields ranging from 70 to 97% and with high purity. Byproducts were not formed. The structures of all products were unambiguously elucidated by NMR spectroscopic methods. In the second part of this work laccase-initiated domino reactions between catechols and heterocyclic 1,3-dicarbonyls have been presented. Using pyridinones, quinolinones and thiocoumarin as substrates, the corresponding benzofuropyridinones, benzofuroquinolinones and thiocoumestans were being obtained. The reactions could be easily performed to deliver the products regioselctively in yields ranging between 55 and 98%. In contrast, polycyclic dispiropyrimidinones were exclusively formed when barbituric acid derivatives were employed as substrates. The unambiguous and complete structure elucidation of all products has been achieved by NMR spectroscopic methods (HSQMBC and band-selective HMBC) as well as by X-ray crystal structure analysis. In the third part of this work laccase-catalyzed transformations between differently substituted hydroquinones and 1,3-dicarbonyls have been studied. These reactions provide a new and highly selective method for the formation of quinone bisadducts with two adjacent 1,3-dicarbonyl substituents. The only exception is the reaction of 2-chlorohydroquinone with 4-hydroxycoumarin which delivers a trisadduct. It is noteworthy that under different conditions the reaction between hydroquinones and 1,3-dicarbonyls resulted in the formation of benzofuran derivatives. The unambiguous structure elucidation of all products has been achieved by NMR spectroscopic methods including spin pattern analysis of the long-range coupled C=O carbons and 13C satellites analysis in 1H NMR spectra. The domino reactions presented in this thesis allow for the efficient and selective synthesis of numerous heterocyclic systems as well as substituted p-benzoquinones under mild reaction conditions. In most cases the products can be isolated in good to very good yields and with high purity. For the structure elucidation of the products a wide range of NMR methods was used.
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.