Browsing by Subject "Phenole"

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Highlighting outstanding beetroot varieties for the food industry - Evaluation of agronomic and compositional attributes of organically grown beetroot (Beta vulgaris L. subsp. vulgaris) varieties
(2022) Yasaminshirazi, Khadijeh; Graeff-Hönninger, Simone
The constant increase in awareness of the relationship between health and diet changed consumers’ perception of food and, accordingly, their food products’ choices. In this regard, the demand for foods, which promote mental and physical health and prevent specific diseases, has increased. Due to its high amount of bioactive compounds, which permits the reformulation of conventional products and transformation of them into functional foods, beetroot (Beta vulgaris L. subsp. vulgaris) was classified as a superfood. On account of the rising demand for organic food products, there is a necessity for varieties, which are adapted to the special requirements of organic farming. Alongside growing beetroot genotypes with desirable agronomic performances and promising contents of bioactive compounds, preserving the quality of harvested beetroots for an extended time can prolong the availability and use of this crop. Hence, affordable and easy-accessible possibilities for prolonging the shelf life of beetroot are required. This thesis aimed to disclose the genetic potential of a broad assortment of new and existing open-pollinated beetroot genotypes, which perform desirably in terms of agronomic and morphological traits (Publication I), compositional characteristics (Publication II), and quality stability (Publication III) under organic farming conditions. In this respect, in total, six genotype-screening field experiments were conducted in 2017 and 2018 at three different locations. Results of the first publication depicted a significant impact of genotype on the total and marketable yields, as well as most of the assessed morphological traits, including skin smoothness, corky surface, and beet shape uniformity. With the analysis of the contents of the total dry matter, total soluble sugar, nitrate, betalains, and total phenolic compounds in the second publication, significant differences were found between 15 studied beetroot genotypes. In addition, the outcome of the third publication demonstrated a significant effect of genotype on all measured compounds of 36 examined beetroot genotypes. Furthermore, the extent of change in the compositional quality during four months of cold storage was assessed for all studied genotypes. On account of the existing genetic variability in beetroot, it was concluded that the intended final utilization should be taken into account for the selection of suitable genotypes. In addition to the conducted assessments in Publication I – III, in the overall project framework from which this thesis was derived, the sensory characteristics of selected open-pollinated genotypes were compared with the commercially used varieties. Three sensory tests were carried out at the University of Hohenheim to determine consumers’ perception of the desired beetroot taste characteristics, including sweetness, aroma intensity, bitterness, earthy flavour, and the degree of acceptability. Generally seen, the studied open-pollinated genotypes indicated more sweetness and less bitterness compared to the F1 hybrid varieties. Furthermore, this thesis assessed the impact of nitrogen fertilisation level on selected compounds (nitrate and total soluble sugar contents) of specific genotypes (Borus, Ronjana, and Regulski Okragly) at the University of Hohenheim in 2018 and 2019. The outcomes indicated no significant influence of the N fertilisation rate on the total soluble sugar content. However, the impacts of fertilisation level and interactions between year and replication on the nitrate content were significant. Consequently, with adjusted N fertilisation, the amount of nitrate in beetroot can be directed in the desired direction based on the intended product (for example, sport drinks with high nitrate levels, and baby food with low nitrate levels). Nevertheless, in the pool of the investigated genotypes in Publication III, some genotypes possessed a comparable nitrate content with the highest values reached by using additional N-fertilisation in this experiment. To conclude, with the investigation of a broad assortment of beetroot genotypes, the findings of the present thesis revealed a high genetic variability regarding yield, morphological and compositional characteristics of beetroot, which provide new possibilities for farmers, the food industry, and consumers. To ensure the competency of the studied genotypes, further studies concerning the determination of other taste-relevant compounds like geosmin and disputable compounds such as oxalic acid are highly recommended. Moreover, to extend the use of the functional properties of fresh beetroot throughout the year, besides the selection of a suitable genotype, the external factors, such as storage conditions, should be optimized as well.
Investigations into the secondary metabolite profile and bioactivity characteristics of various Achillea species grown under different environmental conditions
(2022) Salomon, Lysanne; Kammerer, Dietmar R.
Various Achillea species, including common yarrow Achillea millefolium L., are known to be rich in bioactive substances and are important medicinal plants in modern phytotherapy. In contrast, the alpine species Achillea atrata L. has hardly been studied so far regarding its bioactive compounds and the concomitant potential for human health. Having this in mind, the present work combined studies on the cultivation of A. atrata in different habitats with the phytochemical characterization of its secondary metabolite profile aiming at the generation of plant material with a defined and consistent phenolic profile suitable for pharmaceutical application. Particular emphasis was put on potential relationships between phytochemical profile and bioactivity, and these parameters were considered in comparison with other Achillea species. The results presented in this thesis reveal that the cultivation of A. atrata can be realized at sites differing significantly in altitude and, consequently, in their climatic conditions. Environmental conditions were found to have only a minor impact on the secondary metabolite profile. Rather, differences of various chemotypes might be more decisive. However, the contents of individual phenolic components, especially phenolic acids, is strongly dependent on environmental factors and reach their maximum at increasing altitude levels. Significant differences in the occurrence of the identified phenolic compounds were found between flowers and leaves. In addition to the previously mentioned studies, A. millefolium, Achillea moschata Wulfen, and A. atrata were compared with respect to their phenolic profile and antibacterial activity against gram-positive bacterial strains (Staphylococcus, Propionibacterium). A. atrata showed more similarities in the secondary metabolite profile with the alpine A. moschata than with A. millefolium. The two alpine Achillea species only differed in the occurrence of four compounds. All three aforementioned Achillea species reduced the growth of the tested bacteria. A. atrata showed the highest activity against Propionibacterium acnes and Staphylococcus epidermidis, which are involved in the development of the skin disease Acne vulgaris. In addition, A. atrata exhibited pronounced anti-MRSA potential. Bioassay-guided fractionation of the corresponding extracts revealed that the high antimicrobial activity was due to the flavonoids apigenin, centaureidin, and nevadensin, which were detected exclusively in the most polar fraction and were present in high amounts in A. atrata. Additional studies on the bioactivity and phytochemistry of A. atrata proved that this species exhibits higher antioxidant activity compared to A. millefolium, which was significantly correlated with its total phenolic content. Further bioassay-guided fractionation confirmed the correlation between the mentioned flavonoids in the most polar fraction and the high antioxidant capacity of A. atrata. In conclusion, A. atrata may be an alternative source for the development of novel herbal drugs, based on its compound and bioactivity characteristics.
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.