Anthocyanins are flavonoids which produce blue, purple red and
intermediate colours in plants. They are present as glycosides with an
anthocyanidin C6-C3-C6 skeleton, whose structure is dependent on pH.
Anthocyanins are poorly detected from the biological fluids: plasma and urine.
They may be poorly absorbed or they undergo changes in their structure.
Nevertheless, large amounts of the ingested compounds are likely to enter the
colon either within the matrix of the dietary source or through enterohepatic
circulation. In vitro and in vivo studies have shown that colonic bacteria
transform various flavonoids to smaller phenolic acids. However, there is very
little information on bacterial transformations of anthocyanins.
Aims of the study were to find out the release and changes of anthocyanins in
the in vitro upper intestinal model and their bacterial metabolism in the
colon model. Frozen berries, bilberry (Vaccinium myrtillus) and red raspberry
(Rebus idaeus, v. Ottawa), were subjected to physiological conditions in the
presence and absence of active or heat-inactivated alimentary enzymes
(salivary amylase, pepsin, pancreatin and mucin) in successive stages of
mouth, stomach and duodenum. Changes in stomach and duodenum were compared for
their anthocyanin response by HPLC detected at 520 nm. Bacterial
transformations of pure anthocyanins (cyanidin-3-glucoside and -rutinoside)
isolated from red blum (Prunus domestica L.) and red grapes (Vitis vinifera
L.) were studied in an in vitro colon model using human faecal microbiota as
an inoculum. Metabolites were analysed and characterized by HPLC-DAS and
LC-MS. They were identified by comparing their characteristics with those of
available standards, and semi-quantified using the amount of substrate
analysed from samples at initial timepoint.
Anthocyanins gave a good response as flavylium cations in 520 nm in acidic
conditions mimicking stomach and the detection was decreased dramatically in
neutral to mildly basic conditions of duodenum indicating opening of the
flavylium cation to quinoidal base. In the colon model in vitro
cyanidin-3-rutinoside and cyanidin-3-glucoside were deglycosylated and
formation of three low molecular weight metabolites were shown. The major
metabolite at earlier time points was identified as protocatechuic acid.
Furthermore, reconjugation of the aglycone with other groups, non-typical for
dietary anthocyanins, was evident at the later timepoints.
In conclusion, anthocyanins are poorly detected due to their pH dependent
structural characteristics and their bioavailability is difficult to define on
the basis of detection of flavylium cations only. Also, smaller molecular
weight metabolites are formed due to bacterial actions in the colon, which
involve the cleavage of glycosidic linkages, breakdown of the anthocyanidin
heterocycle and reconjugation of the aglycone. Information about the health
effects of the bacterial metabolites in general is scarce and therefore
research directed to this area is necessary.
|Title of host publication
|Polyphenols communications 2004
|Antti Hoikkala, Otto Soidinsalo
|Place of Publication
|Published - 2004
|MoE publication type
|B3 Non-refereed article in conference proceedings
|Polyphenols Communications 2004: XXII International Conference on Polyphenols - Helsinki, Finland
Duration: 25 Aug 2004 → 28 Aug 2004
|Polyphenols Communications 2004
|25/08/04 → 28/08/04