Abstract
Polyphenols are often ingested alongside dietary fibres. They are both catabolised by, and may influence, the intestinal microbiota; yet, interactions between them and the impact on their resultant microbial products are poorly understood. Dietary fibres (inulin, pectin, psyllium, pyrodextrin, wheat bran, cellulose—three doses) were fermented in vitro with human faeces (n = 10) with and without rutin (20 µg/mL), a common dietary flavonol glycoside. Twenty-eight phenolic metabolites and short chain fatty acids (SCFA) were measured over 24 h. Several phenolic metabolites were produced during fibre fermentation, without rutin. With rutin, 3,4-dihydroxyphenylacetic acid (3,4diOHPAA), 3-hydroxyphenylacetic acid (3OHPAA), 3-(3 hydroxyphenyl)propionic acid (3OHPPA) and 3-(3,4-dihydroxyphenyl)propionic acid (3,4diOHPPA; DOPAC) were produced, with 3,4diOHPAA the most abundant, confirmed by fermentation of 13C labelled quercetin. The addition of inulin, wheat bran or pyrodextrin increased 3,4diOHPAA 2 2.5-fold over 24 h (p < 0.05). Rutin affected SCFA production, but this depended on fibre, fibre concentration and timepoint. With inulin, rutin increased pH at 6 h from 4.9 to 5.6 (p = 0.01) but increased propionic, butyric and isovaleric acid (1.9, 1.6 and 5-fold, p < 0.05 at 24 h). Interactions between fibre and phenolics modify production of phenolic acids and SCFA and may be key in enhancing health benefits.
Highlights
Intake of plant phenolics is estimated to be ~1 g per day [1,2,3] in most populations, a small proportion of which are flavonols [3,4]
Despite the previous observations that rutin formed only a limited set of metabolites in fermentations without fibres, we investigated its effect on the whole profile of phenolic acids using a three-way MANOVA with fibre, concentration and rutin addition as factors
Dietary fibres showed differential interactions with dietary rutin which affected the pattern of phenolic acid and short chain fatty acids (SCFA) production
Summary
Intake of plant phenolics is estimated to be ~1 g per day [1,2,3] in most populations, a small proportion of which are flavonols [3,4]. Rutin is an abundant glycosidic form of quercetin, found in significant quantities in capers, black olives and buckwheat (332, 45 and 36 mg/100 g fresh food weight, respectively) [7]. Drupe fruits such as blackcurrants and raspberries may provide up to 11 mg of rutin per 100 g [7,8]. Most ingested rutin enters the colon, where it is catabolised by the gut microbiota via a pathway starting with the hydrolytic cleavage of the disaccharide moiety [19,20,21]
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