Abstract
Flavonols and flavanones are polyphenols exerting many healthy biological activities. They are often glycosylated by rutinose, which hampers absorption in the small intestine. Therefore they require the gut microbiota to release the aglycone and enable colonic absorption. The role of the gut microbiota and bifidobacteria in the release of the aglycones from two major rutinosides, hesperidin and rutin, was investigated. In bioconversion experiments, the microbiota removed rutinose from both rutin and hesperidin, even though complete hydrolysis was not obtained. To investigate whether bifidobacteria can participate to the hydrolysis of rutinosides, 33 strains were screened. Rutin was resistant to hydrolysis by all the strains. Among six tested species, mostly Bifidobacterium catenulatum and Bifidobacterium pseudocatenultum were able to hydrolyze hesperidin, by means of a cell-associated activity. This result is in agreement with the presence of a putative α-l-rhamnosidase in the genome of B. pseudocatenulatum, while most of the available genome sequences of bifidobacteria aside from this species do not bear this sequence. Even though B. pseudocatenulatum may contribute to the release of the aglycone from certain rutinose-conjugated polyphenols, such as hesperidin, it remains to be clarified whether this species may exert a role in affecting the bioavailability of the rutinoside in vivo.
Highlights
Plants are dietary sources of hundreds of polyphenols with beneficial biological activities.Polyphenols are classified as phenolic acids, flavonoids, stilbenes, lignans, hydrolyzable tannins, and condensed tannins on the basis of the number of phenol rings and the structure elements which connect them, with flavonoids clustered into flavonols, flavones, isoflavones, flavanones, anthocyanidins, and flavanols [1]
This study aims to focus on the involvement of bifidobacteria in the hydrolysis of the major rutinosides rutin and hesperidin, taking into account the inter-individual variability of transformation of these conjugated flavonoids by colonic microbiota
The transformation of rutin and hesperidin was observed after 24 h incubation with the resting cells of human gut microbiota from nine different healthy volunteers
Summary
Polyphenols are classified as phenolic acids, flavonoids, stilbenes, lignans, hydrolyzable tannins, and condensed tannins on the basis of the number of phenol rings and the structure elements which connect them, with flavonoids clustered into flavonols, flavones, isoflavones, flavanones, anthocyanidins, and flavanols [1]. Flavonols and flavanones are antioxidants, and exert many health effects which include anti-inflammatory effects and protective activities against breast and gastrointestinal cancer and cardiovascular diseases [2,3,4]. Quercetin is the most abundant flavonol, followed by kaempferol. These compounds generally occur in glycosylated form, bound to glucose, rhamnose, or rutinose, the most widespread glycosidic form of quercetin being its rutinoside, rutin (Figure 1) [1]. Flavanones are less common than flavonols, but they are present in high concentrations in citrus fruit, in the albedo
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