Cardoon stalks and sweet pepper fruits: in vitro approach to their potential genoprotective, anti-inflammatory and prebiotic activity in the gastrointestinal tract, before and after culinary treatment

Polyphenols have shown ability to modulate DNA damage, inflammation, and the gut microbiota. Cardoon stalks (Cynara cardunculus var. L. altilis DC) and sweet Italian green peppers fruits (Capsicum annuum L.) are vegetables with different polyphenolic profile (chlorogenic acids vs flavonoids respectively). Thus, the main aim of this project was to evaluate the potential genoprotective and/or anti-inflammatory and prebiotic activity of cardoon stalks and sweet Italian green pepper fruits in the gastrointestinal (GI) tract, by simulating an intake situation. A total of 30 polyphenols were identified and quantified by HPLC-MS/MS in white and red cardoon stalks. Red cardoon almost doubled the polyphenol content of white cardoon, and was therefore selected for the assessment of its biological activity. Besides, the impact of 4 heat treatments (i.e., blanching, different frying conditions, traditional boiling and sous-vide cooking) on the antioxidant capacity and/or the polyphenol profile and content of cardoon stalks, was evaluated. Then, sous-vide cooking was selected for red cardoon, and griddling for green pepper, as they favour a high polyphenol bioaccessibility after GI digestion. Bioaccessible polyphenols of GI-digested green pepper did not show genoprotection against oxidatively generated damage in HT-29 cells, regardless of the application of a heat treatment (griddling). Besides, high polyphenol concentrations caused a slight pro-oxidant effect on DNA. GI-digested raw red cardoon and raw green pepper had <1 and 78% of bioaccessible polyphenols, respectively, and exerted anti-inflammatory activity against lipopolysaccharide-induced secretion of cytokines in Caco-2 cells. This anti-inflammatory effect was more effective in cardoon than in pepper. In addition, high concentration of digested raw pepper revealed pro-inflammatory activity. The application of a heat treatment on the vegetables had a negative impact on their anti-inflammatory activity. In fact, GI-digested sous-vide cooked cardoon (60% bioaccessible polyphenols) induced pro-inflammatory effects at high concentration, while digested griddled pepper (80% bioaccessible polyphenols) showed lower anti- and pro-inflammatory activity than digested raw pepper. On the other hand, red cardoon and green pepper after 8 and 24 h of colonic fermentation showed great differences in their content of polyphenols and catabolites, but did not show anti-inflammatory activity in HT-29 cells. Both red cardoon and green pepper showed in vitro prebiotic activity on human gut microbiota, comparable to commercial prebiotic fructooligosaccharides, by stimulating Bifidobacterium spp., and by increasing acetate production mainly. Red cardoon also stimulated Lactobacillus/enterococcus group. The application of sous-vide cooking in red cardoon and griddling in green pepper enhanced the bifidogenic effect. In summary, bioaccessible polyphenols from both GI-digested red cardoon and green pepper seem to exert anti-inflammatory activity at low concentration, but DNA pro-oxidant and/or pro-inflammatory activity at high concentration in intestinal cells, at simulated physiological concentrations. Both red cardoon and green pepper exert in vitro prebiotic activity on the human gut microbiota. Finally, the application of a heat treatment enlarges the polyphenol bioaccessibility, inhibits the anti-inflammatory activity, and enhances the prebiotic activity of both vegetables