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Background: Strong interindividual differences in the microbial conversion of some dietary polyphenols have been reported. In-depth studies of trans-resveratrol metabolism by human gut microbiota, however, are lacking, and only one bacterial metabolite, namely dihydroresveratrol, has been described. Objective: The aim of this study was to elucidate interindividual differences in trans-resveratrol metabolism by human gut microbiota and to identify bacterial strains involved. Design: In the first part of the study, in vitro fermentation experiments were performed with feces samples from 7 healthy volunteers, and metabolite formation was measured by liquid chromatographyultraviolet/visible (UV/Vis)-mass spectrometry (MS)/MS detection. Microbial diversities in 3 feces samples were analyzed by high-throughput pyrosequencing and quantitative real-time polymerase chain reaction. In addition, trans-resveratrol conversion experiments were conducted with selected fecal bacterial strains in pure culture. The second part of the study was a controlled intervention study with 12 healthy volunteers. After a washout period, all of the subjects received a one-time oral dose of 0.5 mg trans-resveratrol/kg body weight in the form of a grapevine-shoot supplement, and 24-h urine samples were analyzed by liquid chromatography-UV/Vis-MS/MS. Results: Besides dihydroresveratrol, 2 previously unknown bacterial trans-resveratrol metabolites were identified in vitro and in vivo: 3,4'-dihydroxy-trans-stilbene and 3,4'-dihydroxybibenzyl (lunularin). Their formation, however, varied among the volunteers. Two strains, Slackia equolifaciens and Adlercreutzia equolifaciens, were identified as dihydroresveratrol producers. Gut bacteria able to produce dehydroxylated metabolites could, however, not be identified. Conclusions: trans-Resveratrol metabolism by human gut microbiota shows pronounced interindividual differences, which should be taken into account during investigation of health-related effects of this stilbene. This trial was registered at the German Clinical Trials Register as DRKS00004311, Universal Trial Number (WHO) UTN: U1111-1133-4621. [ABSTRACT FROM AUTHOR]

Borago officinalis (borage) is widely consumed as a herb or vegetable, however, it produces toxic pyrrolizidine alkaloids (PA). In 2020, the European Union (EU) established maximum levels for the PA content in certain foodstuffs, including borage leaves. This study aimed to evaluate PA contents and profiles in borage originating from different cultivation conditions and developmental stages. A total of 106 borage leaf samples, including borage microgreens, leaves from commercial producers, and plants from various home gardens at pre-flowering, flowering and end-of-flower stages, as well as 33 flower samples from plants grown in home gardens, were analyzed. The microgreens exhibited strikingly high PA contents, exceeding the maximum level set by Commission Regulation (EU) 2023/915 by an average factor of 130. PA contents in the leaves of pre-flowering plants exceeded the maximum level by an average factor of 5, whereas PA contents in the leaves of flowering plants were below the maximum level in most cases. The PA contents in flowers were higher than those of the corresponding leaves, suggesting increased accumulation of PA in flowers compared to leaves. Additionally, the occurrence of acetylated PA, especially 7-acetyl-lycopsamine- N -oxide, which are not listed in the EU regulation, was shown to be significant in borage. In summary, our results indicate that the PA contents in borage leaves are highest in emerging plants and decrease with the progression of plant or leaf maturity. The findings suggest that borage microgreens may not be suitable for human consumption and that further regulatory consideration of acetylated PA is warranted. • Borage microgreens pose a food safety concern due to high PA contents. • Developmental stage of borage influences the PA content in leaves. • Borage contains relevant levels of acetylated PA not covered by the EU legislation. • The PA contents of borage flowers were higher than those of the leaves. [ABSTRACT FROM AUTHOR]

Vegetables can be important dietary sources of vitamin E. However, data on vitamin E in raw and cooked vegetables are in part conflicting, indicating analytical pitfalls. The purpose of the study was to develop and validate an HPLC-FLD method for tocochromanol (tocopherols and tocotrienols) analysis equally suitable for raw and cooked vegetables. Significant instability of tocochromanols was observed in raw broccoli and carrot homogenates. Tocochromanols could be stabilized by freeze-drying or ascorbic acid addition prior to homogenization. The optimized protocol for tocochromanol analysis included knife and ball milling of freeze-dried vegetable pieces. Direct acetone extraction of vegetable powders allowed for satisfactory recoveries and precisions. A significant decrease of tocochromanols in baked compared to raw vegetables was shown, the extent of which varied largely between vegetables. For some raw vegetables, such as spinach or broccoli, underestimation of vitamin E in nutrient databases cannot be ruled out and should be examined. [ABSTRACT FROM AUTHOR]