Cactus cladodes (Opuntia ficus-indica) as a dietary source of bioaccessible (poly)phenols: effect of heat treatment, gastrointestinal digestion and human gut microbiota action, and bioactivity in colon

Abstract

Cactus (Opuntia ficus-indica Mill.) cladodes, commonly eaten as a fresh or cooked vegetable, present a great amount of (poly)phenolic compounds which can be modified by cooking treatments, gastrointestinal digestion and the human gut microbiota. Likewise, (poly)phenols could be able to exert their biological activity into the colon cells. Therefore, the main aim of this work was to evaluate the impact of heat treatment (boiling, microwaving, griddling, and frying in olive and soybean oils) on nutritional composition, antioxidant capacity and (poly)phenols profile of cactus cladodes, as well as their bioaccessibility after an in vitro gastrointestinal digestion and colonic fermentation. Moreover, the potential biological activity of colonic fermented cactus cladodes in HT29 colon cells was assessed. Previously, the extraction method of (poly)phenolic compounds with several solvents and conditions was optimized, selecting a combination of methanol, acetone and water as the best one. In addition, acid hydrolysis conditions were also optimized in order to identify and quantify (poly)phenol aglycones by HPLC-DAD analysis.

Culinary processes, except boiling, increased soluble and insoluble fibre up to 5.0 g/100 g, becoming cactus cladodes a good fibre source. Likewise, heat treatments increased the total phenolic content measured by Folin-Ciocalteu in cactus cladodes, except in boiled ones due to the leaching losses. A total of 45 (poly)phenols were identified and quantified in raw and cooked cactus cladodes by UHPLC-PDA-HR-MS, predominating flavonoids (60−68% total), mainly isorhamnetin derivatives, and phenolic acids (32−40%) with eucomic acids as the predominant ones. Microwaving (1.4-fold) and griddling (1.2-fold) increased the total amount of compounds while both frying (0.6-fold) and boiling (0.9-fold) produced a decrease. Additionally, antioxidant capacity was measured, which was also increased after cooking treatments applied.

Gastrointestinal digestion significantly (p<0.05) decreased (poly)phenolic compounds showing flavonoids a higher retention or degradation (37&#8722;63% bioaccessibility) than phenolic acids (56&#8722;87% bioaccessibility). Furthermore, gastrointestinal digestion induced isomerizations among piscidic and eucomic acids. The human gut microbiota also produced a higher degradation in flavonoids than in phenolic acids. However, some compounds still remained after 24 h of colonic fermentation, being eucomic acid as the most relevant. Cactus cladodes after the action of colonic microbiota showed an antigenotoxic effect on HT29 colon cells, reducing the H2O2-induced DNA damage.