Bioaccessibility and antioxidant activity of Calendula officinalis supercritical extract as affected by in vitro co-digestion with lipids

Abstract

Calendula officinalis (marigold) is an interesting source of terpenes of bioactive interest, mainly pentacyclic triterpenes (PT). Supercritical extracts of marigold (ME), in absence and presence of co-solvent (ethanol), were produced and characterized. The bioaccessibility of terpenes and the distribution of particle sizes after in vitro gastrointestinal digestion affected by the coexistence of olive oil (OO) were determined. The impact of the gastrointestinal process on the antioxidant activity of the ME was also evaluated by the DPPH assay. The major quantified compounds of the extracts in absence of co-solvent were the bioactive PT taraxasterol, lupeol, D-amyrin and β-amyrin. The total amount of quantified compounds was lower in case of the ethanol-CO2 extract. The bioaccessibility decreased in the following order: sesquiterpenes hydrocarbons > oxygenated sesquiterpenes > oxygenated triterpenes > alkanes. PT showed high values of bioaccessibility (>75%), whereas such value was lower than 50% for other compounds of the extract. A negative correlation was found between molecular properties of the compounds (logP and number of rotatable bonds) and bioaccessibility. The coexistence of ME with OO during in vitro digestion enhanced the bioaccessibility of most compounds, being closer to 100% for most PT. In agreement with these results, a higher abundance of particles of lower sizes within the aqueous micellar phase after digestion of the ME+OO were found compared with the absence of OO (most particles sizes lower than 28 ½m and 192 ½m, respectively). On the other hand, the antioxidant activity of ME increased after gastrointestinal digestion up to 50%, regardless of OO. Supercritical CO2 extraction in absence of co-solvent is the preferred procedure for producing a ME richer in PT. Furthermore, in spite of the proper bioaccessibility, the co-digestion with low levels of a typical dietary fat would be enough to reach a complete bioaccessibility of PT, due to a better dispersion of the extract in the aqueous media of digestion. Additionally, the gastrointestinal process enhances the antioxidant effect of the ME, regardless of the coexistence of oil.