Interactions Between Dietary Anthocyanins and the Human Gut Microbiota

Shehata, Emad (2022) Interactions Between Dietary Anthocyanins and the Human Gut Microbiota. Doctoral thesis, University of East Anglia.

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Background: Consumption of dietary anthocyanins has been associated with various health benefits. However, anthocyanins are known to be very poorly bioavailable, and this has led to the concept that there is an important interplay between anthocyanins and the human gut microbiota, where the gut microbiota are able to break down anthocyanins into various metabolites, and that anthocyanins and/or their metabolites may alter the composition of the gut microbiota. However, these interactions are still not clear and much remains to be understood.

Objectives: (i) Investigate the in-vitro metabolism of black rice and bilberry anthocyanins by the gut microbiota and (ii) explore the impact of anthocyanins on the structure and function of the gut microbiota.

Approaches: Incubate black rice and bilberry anthocyanins over 24 h with human faecal samples using an in-vitro batch colon fermentation model and collect samples for quantifying anthocyanins and anthocyanin metabolites using HPLC-DAD and UPLC-MS-MS. Assess the gut microbiota composition differences between anthocyanin treated and non-anthocyanin treated human colon model samples using whole-genome shotgun metagenomics.

Results: It was shown that loss of anthocyanins was partly spontaneous and partly due to the gut microbiota. Anthocyanins were subject to high inter-individual variations in both spontaneous and gut microbiota-dependent degradation, and modest intra-individual variations. The gut microbiota metabolism (enzymatic) of anthocyanins generates various ring-fission metabolites, and various microbial metabolic pathways were determined such as [Cya3Glc → PCA → catechol], [Cya3Glc → PGA → PGCA→ phloroglucinol], and [Cya3Glc → dihydroferulic acid → dihydrocaffeic acid → 4-methylcatechol]. The production of the microbial anthocyanin metabolites such as catechol, dihydrocaffeic acid, dihydroferulic acid, and 4-methylcatechol were completely microbiota-dependent, providing strong evidence that the gut microbiota is important for the metabolism of anthocyanins. In contrast, in the absence of live gut microbiota and in anaerobic conditions, anthocyanins underwent classic pH-dependent transformation to give Cya hemiketal-Glc, Cya chalcone-Glc, Cya chalcone anionic-Glc and trihydroxyethenylbenzene-Glc (all colourless). But under aerobic conditions, there was a substantial increase in the number of anthocyanin breakdown products formed and these included PCA, PGA, coumarin-Glc, di- and tri-hydroxyphenyloxoacetic acid, and trihydroxyphenylacetic acid. Although there was a small increase of Bacteroidetes over Firmicutes at 6 and 12 h and small increase of Bacteroides vulgatus at 6 h, no significant changes were observed in the gut microbiota profile in response to anthocyanin treatments.

Conclusions: Anthocyanins are rapidly and completely degraded in the human colon by a combination of spontaneous and microbiota-dependent processes generating a series of ring fission metabolites, but they did not significantly affect the structure and function of the microbiome. These data extend our understanding of the important role of the human gut microbiota on the bioavailability of consumed anthocyanins.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Kitty Laine
Date Deposited: 12 Dec 2022 17:37
Last Modified: 06 Mar 2023 13:45


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