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The release characteristics of a unique blend of carotenoid beadlets designed to increase bioavailability were tested using the dynamic gastrointestinal model TIM‐1. Individual carotenoid bioaccessibility peaks were observed over approximately 3–4 hr in the order of lutein and zeaxanthin first, followed by lycopene, and then finally α‐ and β‐carotene; when tested as a beadlet blend or when the beadlets were compressed into tablets. Bioaccessibility measurements of 7%–20% were similar to those previously reported in literature and comparable between the two formulations, beadlet blend and tablet formulations. Total recovery of carotenoids from all compartments ranged from 70% to 90% for all carotenoids, except lycopene where almost 50% was unrecoverable after digestion in the TIM system. [ABSTRACT FROM AUTHOR]

This study introduces a stable-isotope metabolic approach employing [U-13C]glucose that, as a novelty, allows selective profiling of the human intestinal microbial metabolic products of carbohydrate food components, as well as the measurement of the kinetics of their formation pathways, in a single experiment. A well-established, validated in vitro model of human intestinal fermentation was inoculated with standardized gastrointestinal microbiota from volunteers. After culture stabilization, [U-13C]glucose was added as an isotopically labeled metabolic precursor. System lumen and dialysate samples were taken at regular intervals. Metabolite concentrations and isotopic labeling were determined by NMR, GC, and enzymatic methods. The main microbial metabolites were lactate, acetate, butyrate, formate, ethanol, and glycerol. They together accounted for a 13C recovery rate as high as 91.2%. Using an NMR chemical shift prediction approach, several minor products that showed 13C incorporation were identified as organic acids, amino acids, and various alcohols. Using computer modeling of the 12C contents and 13C labeling kinetics, the metabolic fluxes in the gut microbial pathways for synthesis of lactate, formate, acetate, and butyrate were determined separately for glucose and unlabeled background substrates. This novel approach enables the study of the modulation of human intestinal function by single nutrients, providing a new rational basis for achieving control of the short-chain fatty acids profile by manipulating substrate and microbiota composition in a purposeful manner. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Carbohydrates, including starches, are an important energy source for humans, and are known for their interactions with the microbiota in the digestive tract. Largely, those interactions are thought to promote human health. Using 16S ribosomal RNA (rRNA)-based stable isotope probing (SIP), we identified starch-fermenting bacteria under human colon-like conditions. To the microbiota of the TIM-2 in vitro model of the human colon 7.4 g l−1 of [U-13C]-starch was added. RNA extracted from lumen samples after 0 (control), 2, 4 and 8 h was subjected to density-gradient ultracentrifugation. Terminal-restriction fragment length polymorphism (T-RFLP) fingerprinting and phylogenetic analyses of the labelled and unlabelled 16S rRNA suggested populations related to Ruminococcus bromii, Prevotella spp. and Eubacterium rectale to be involved in starch metabolism. Additionally, 16S rRNA related to that of Bifidobacterium adolescentis was abundant in all analysed fractions. While this might be due to the enrichment of high-GC RNA in high-density fractions, it could also indicate an active role in starch fermentation. Comparison of the T-RFLP fingerprints of experiments performed with labelled and unlabelled starch revealed Ruminococcus bromii as the primary degrader in starch fermentation in the studied model, as it was found to solely predominate in the labelled fractions. LC-MS analyses of the lumen and dialysate samples showed that, for both experiments, starch fermentation primarily yielded acetate, butyrate and propionate. Integration of molecular and metabolite data suggests metabolic cross-feeding in the system, where populations related to Ruminococcus bromii are the primary starch degrader, while those related to Prevotella spp., Bifidobacterium adolescentis and Eubacterium rectale might be further involved in the trophic chain. [ABSTRACT FROM AUTHOR]