Complex flavonoids in cocoa: synthesis and degradation by intestinal microbiota.

Rarely occurring flavan-3-ol derivatives such as C-glycosides can be generated during food processing, for example, by cocoa production. These astringent taste compounds may also exert interesting behavior toward microbial metabolism, as other C-glycosides have been shown to be quite stable. Oligomeric flavan-3-ols, the procyanidins, bear also a C-C bond between the main moieties and are suspected to resist microbial metabolism for a prolonged time compared to other flavonoids.

Flavan-3-ol C-glycosides--preparation and model experiments mimicking their human intestinal transit.

In order to study the human intestinal transit of flavan-3-ol C-glycosides, several C-glycosyl derivatives were prepared by non-enzymatic reaction of (+)-catechin with α-D-glucose, α-D-galactose and α-D-rhamnose, respectively. In contrast to literature data, we propose that the reaction mechanism proceeds in analogy to the rearrangement of flavan-3-ols during epimerization under alkaline conditions. Four of the 12 synthesized flavan-3-ol C-glycosides were incubated under aerobic conditions at 37°C using saliva (2 min) and simulated gastric juice (3 h).

Degradation and metabolism of catechin, epigallocatechin-3-gallate (EGCG), and related compounds by the intestinal microbiota in the pig cecum model.

As intestinal metabolism strongly influences the bioavailability of flavonoids, this study investigated the microbial deconjugation and degradation of the most common flavan-3-ols using the pig cecum in vitro model system developed in the authors' group. The microbial degradation of (+)-/(-)-catechin, (-)-epicatechin, (-)-gallocatechin, (-)-epigallocatechin, (-)-gallocatechin gallate, (-)-epigallocatechin gallate, procyanidin B2, and gallic acid was investigated under anaerobic physiological conditions in single incubation experiments and as a mixture. Incubation was done with the microbiota from three different animals in repeat determinations (n = 6).

Deconjugation and degradation of flavonol glycosides by pig cecal microbiota characterized by Fluorescence in situ hybridization (FISH).

As the bioavailability of flavonoids is influenced by intestinal metabolism, we have investigated the microbial deconjugation and degradation of several flavonols and flavonol glycosides using the pig cecum in vitro model system developed in our group. For this model system the microbiota was directly isolated from the cecal lumen of freshly slaughtered pigs. The characterization of the cecal microbiota by fluorescence in situ hybridization (FISH) with 16S rRNA-based oligonucleotide probes confirmed the suitability of the model system for studying intestinal metabolism by the human microbiota.

Synthesis and structure determination of covalent conjugates formed from the sulfury-roasty-smelling 2-furfurylthiol and di- or trihydroxybenzenes and their identification in coffee brew.

Recent investigations demonstrated that the reaction of odor-active thiols such as 2-furfurylthiol with thermally generated chlorogenic acid degradation products is responsible for the rapid aroma staling of coffee beverages. To get a clear understanding of the molecular mechanisms underlying this aroma staling, the existence of putative phenol/thiol conjugates needs to be verified in coffee. The aim of the present study was therefore to synthesize such conjugates for use as reference substances for LC-MS screening of coffee.