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.

Cell wall cross-linking can have a substantial effect on the properties of the wall. To estimate cross-linking (between arabinoxylans) in cereal ®bres, dehydrodiferulate levels were measured in soluble and insoluble dietary ®bre (SDF and IDF) isolated from whole grains of maize (Zea mays L), wheat (Triticum aestivum L), spelt (Triticum spelta L), rice (Oryza sativa L), wild rice (Zizania aquatica L), barley (Hordeum vulgare L), rye (Secale cereale L), oat (Avena sativa L) and millet (Panicum miliaceum L). After saponi®cation of the cereal ®bres the extracts were investigated for dehydrodimers of ferulic acid using GLC±MS and GLC±FID. From most cereal IDF the whole spectrum of dehydrodiferulic acids (DFAs) (8-5'-, 8-8'-, 5-5'-, 8-O-4'-and 4-O-5'-coupled) could be identi®ed. The absolute contents of total DFAs ranged between 2.4 and 12.6 mg g À1. With the exception of 4-O-5'-coupled DFA, the whole range of DFAs was also detected from cereal SDF but only in amounts of 40±230 mg g À1. It was estimated that arabinoxylans of cereal IDF contain 8±39 times more diferulates than arabinoxylans of cereal SDF (where measurement of DFA levels in SDF was possible). In cereal IDF, 8-5'-coupled dimers dominated, whereas in cereal SDF, 8-8'-coupled dimers were relatively enhanced and often became the major dimers.

No abstract

The diet provides carbohydrates that are non-digestible in the upper gut and are major carbon and energy sources for the microbial community in the lower intestine, supporting a complex metabolic network. Fermentation produces the short-chain fatty acids (SCFAs) acetate, propionate and butyrate, which have health-promoting effects for the human host. Here we investigated microbial community changes and SCFA production during in vitro batch incubations of 15 different non-digestible carbohydrates, at two initial pH values with faecal microbiota from three different human donors. To investigate temporal stability and reproducibility, a further experiment was performed 1 year later with four of the carbohydrates. The lower pH (5.5) led to higher butyrate and the higher pH (6.5) to more propionate production. The strongest propionigenic effect was found with rhamnose, followed by galactomannans, whereas fructans and several α- and β-glucans led to higher butyrate production. 16S ribosomal RNA gene-based quantitative PCR analysis of 22 different microbial groups together with 454 sequencing revealed significant stimulation of specific bacteria in response to particular carbohydrates. Some changes were ascribed to metabolite cross-feeding, for example, utilisation by Eubacterium hallii of 1,2-propanediol produced from fermentation of rhamnose by Blautia spp. Despite marked inter-individual differences in microbiota composition, SCFA production was surprisingly reproducible for different carbohydrates, indicating a level of functional redundancy. Interestingly, butyrate formation was influenced not only by the overall % butyrate-producing bacteria in the community but also by the initial pH, consistent with a pH-dependent shift in the stoichiometry of butyrate production.

Ferulate dehydrodimers and the more recently discovered dehydrotrimers play an important role in the cell wall architecture of plant-based foods and forages. High-performance liquid chromatography methods to determine ferulate dimers often lack specificity; methods for trimers did not exist yet. A method for the determination of 11 cell wall-bound ferulate dehydrodimers and -trimers was developed, including the crucial separation of the di/trimers from the often dominating phenolic monomers. Validation parameters for the basic calibration of the dimers and trimers met our acceptance criteria. However, the matrix calibration revealed that lignin-rich matrices lead to problems with precision and accuracy that likely can be addressed by using a more specific detection, that is, mass spectrometric detection, next to improved sample preparation procedures. The method was used to analyze low-lignin fibers from corn, wheat, and rye grains, wild rice, asparagus, and sugar beet. With the exception of wild rice, the 5-5/8-O-4-, 8-O-4/8-O-4-, and 8-8(aryltetralin)/8-O-4-dehydrotrimers were detected in all analyzed samples, however, often in amounts below the limit of quantitation.