Catabolism of raw and cooked green pepper (Capsicum annuum) (poly)phenolic compounds after simulated gastrointestinal digestion and faecal fermentation

A total of 21 (poly)phenolic compounds (free and bound) were quantified in raw, olive oil fried, sunflower oil fried and griddled green pepper before and after a simulated gastrointestinal digestion. Flavonoids, particularly quercetin rhamnoside, were the main compounds. The bioaccessibility of (poly)phenolic compounds after gastrointestinal digestion was higher in cooked (>82%) than in raw (48%) samples, showing a positive effect of heat treatment on the release of (poly)phenols from the vegetal matrix. Additionally, a faecal fermentation was carried out for 24h. A time-dependent microbial metabolic activity was observed, which resulted firstly (<5h) in the hydrolysis of flavonoid glycosides and then in the formation of 3 catabolites, namely 3,4-dihydroxybenzoic acid, dihydrocaffeic acid and 3-(3′-hydroxyphenyl)propionic acid, this being by far the most abundant. Catabolic pathways for colonic microbial degradation of flavonoids and hydroxycinnamic acids have been proposed. Griddled pepper showed the highest amount of (poly)phenols both after gastrointestinal digestion and colonic fermentation.