Maike Passon

Oxidative coupling of caffeic acid esters with primary amino compounds may cause the formation of colored compounds, but there is still uncertainty about the mechanisms and structures, especially when derived from α-amino acids. Therefore, methyl caffeate (MCA) or 5-caffeoylquinic acid (5-CQA) was reacted with either α- or β-alanine, and the products were characterized using UHPLC-DAD-ESI-LIT-MS and UHPLC-DAD-ESI-QToF-MS. For both caffeic acid esters, UV–vis data, fragmentation patterns, and exact masses revealed the formation of analogous reaction products, supposedly based on a benzacridine core. However, data derived from model systems based on MCA were less complex due to the absence of acyl migration. As expected, presumed N-unsubstituted benzacridines were found with α- but not β-alanine, whereas N-substituted benzacridines were surprisingly found with both. The findings expand current knowledge of benzacridine formation from different precursors and provide a sound basis for the generation of reference substances and studies in real food systems.

Improving the quality of compounds in medicinal and aromatic plants is crucial due to their uses in the pharmaceutical, cosmetics, and food sectors. One way of influencing plant composition is through exposure to different light conditions. Therefore, a two-year field study (2023–2024) was conducted to investigate the impact of coloured shading nets on the physiology, essential oil (EO) content, and composition of three Mentha genotypes: Mentha × piperita ‘Multimentha’, Mentha × piperita ‘Fränkische Blaue’, and Mentha rotundifolia ‘Apfelminze’. In addition to an unshaded control, the Mentha plants were grown under red and blue shading nets. Plant height and vegetation indices were collected weekly. Biomass accumulation, EO content, and composition were determined for each harvest. Both red and blue shading were found to influence the physiological responses and EO compositions of the plants, with red shading promoting slightly higher p-menthone levels in ‘Fränkische Blaue’ and ‘Multimentha’, while blue shading slightly increased carvone levels in ‘Apfelminze’. While EO content varied across harvest seasons (spring, summer, and autumn), ‘Fränkische Blaue’ responded to red shading, demonstrating an increased EO content. The findings suggest that targeted use of coloured shading nets can modulate EO quality. However, genotype-specific responses highlight the necessity of further research to define shading applications for different species and genotypes.

Mentha spp. are commonly used for the production of tea and for the extraction of essential oils (EOs). The key factor of mint quality is the content and composition of the EO. Health-promoting compounds such as menthol are desirable, whereas the presence of potentially health-damaging compounds such as menthofuran should be avoided. This study examines the effect of shading on the EO content and composition of three Mentha genotypes (Mentha × piperita ‘Multimentha’, Mentha × piperita ‘Fränkische Blaue’ and Mentha rotundifolia ‘Apfelminze’). The Mentha genotypes were cultivated in field trials for two years (2022–2023). Each genotype was shaded with a shading net (50% photosynthetic active radiation (PAR) reduction), and a control without shading was prepared. EO content was determined by steam distillation and EO composition was characterized by GC-MS analysis. Furthermore, biomass, vegetation indices (VIs) and the electron transport rate (ETR) were analyzed. While shading led to higher plant heights, higher EO content and a slightly reduced amount of undesired EO compounds, the unshaded control yielded a higher biomass accumulation. Significant genotypic differences were determined. In conclusion, the benefits of shading depend on the intended use and genotype selection.

Mentha sp. is commonly used for essential oil (EO) extraction and incorporated in multiple products of food and pharmaceutical industries. Postharvest management is a key factor in line of production to preserve quality-determining plant ingredients. This study focused on the effects of two different postharvest processes on EO content and the composition of three different Mentha genotypes (Mentha × piperita ‘Multimentha’, Mentha × piperita ‘Fränkische Blaue’ and Mentha rotundifolia ‘Apfelminze’). They were cultivated under greenhouse conditions. One postharvest treatment consisted of drying Mentha as whole plant after harvesting and later separating leaves from stems. In the second treatment, leaves were separated from stems directly after harvesting and then dried. EO content was determined by steam distillation and composition of EO was characterized by GC/MS analysis. Key findings of the study are that the postharvest processing treatments had no significant influence on the content or composition of the EO. Only the genotype ‘Fränkische Blaue’ showed a significantly higher EO content in the dry separated treatment at the third harvest (2.9 ± 0.15 mL/100 g DM (sD)) than separated fresh (2.4 ± 0.24 mL/100 g DM (sF)). However, genotype selection and harvest time had a clear impact on EO content and composition.

The metabolism of anthocyanins in humans is still not fully understood, which is partly due to the lack of reference compounds. It is known that sulfation is one way of the complex phase II biotransformation mechanism. Therefore, cyanidin-3-O-glucoside and the cyanidin aglycone were chemically converted to their sulfates by reaction with sulfur trioxide-N-triethylamine complex in dimethylformamide. The reaction products were characterized by UHPLC coupled to linear ion trap and IMS-QTOF mass spectrometry. Based on MS data, retention times, and UV-Vis spectra, the compounds could tentatively be assigned to A-, C-, or B-ring sulfates. Analysis of urine samples from two volunteers after ingestion of commercial blackberry nectar demonstrated the presence of two sulfated derivatives of the cyanidin aglycone and one sulfated derivative of the cyanidin-3-O-glucoside. It was found that both the A ring and the B ring are sulfated by human enzymes. This study marks an important step toward a better understanding of anthocyanin metabolism.

The approach presented in this study is the first for the hemisynthesis of methylated anthocyanins. It was possible to obtain cyanidin-3-O-glucoside derivatives with different degrees of methylation. Cautious identification of 4′-, 5-, and 7-OH monomethylated derivatives was also accomplished. The methylation agent used was the “green chemical” dimethyl carbonate (DMC), which is characterized by low human and ecological toxicity. The influence of the temperature, reaction time, and amount of the required diazabicyclo[5.4.0]undec-7-en (DBU) catalyst on the formation of the products was examined. Compared to conventional synthesis methods for methylated flavonoids using DMC and DBU, the conditions identified in this study result in a reduction of reaction time, and an important side reaction, so-called carboxymethylation, was minimized by using higher amounts of catalyst.

Introduction: Craterostigma plantagineum and Lindernia brevidens are resurrection plants, so these plants can tolerate desiccation of their vegetative tissues. Different components and mechanisms contribute to desiccation tolerance and secondary plant metabolites, like phenolic compounds, may play a role during these processes.Objectives: Secondary plant metabolites of the two resurrection plants, C. plantagineum and L. brevidens as well as the closely related desiccation sensitive species, L. subracemosa, were investigated regarding the polyphenol profile.Material and methods: Secondary plant compounds were extracted with acidified methanol and analysed with ultra‐high‐performance liquid chromatography electrospray ionisation mass spectrometry (UHPLC‐ESI‐MS). Phenolic compounds were identified by comparing of ultraviolet (UV) and MSⁿ‐spectra with published data. All compounds were quantified as verbascoside equivalents by external calibration at the compound specific wavelength.Results: In total, eight compounds that belong to the subclass of phenylethanoid glycosides and one flavone, luteolin hexoside pentoside, were identified. Two of these compounds exhibited a fragmentation pattern, which is closely related to phenylethanoid glycosides. The predominantly synthesised phenylethanoid in all of the three plant species and in every stage of hydration was verbascoside. The total content of phenolic compounds during the three stages of hydration, untreated, desiccated, and rehydrated revealed differences especially between C. plantagineum and L. brevidens as the latter one lost almost all phenolic compounds during rehydration.Conclusion: The amount of verbascoside correlates with the degree of desiccation tolerance and verbascoside might play a role in the protective system in acting as an antioxidant.