In vitro absorption and antiproliferative activities of monomeric and polymeric anthocyanin fractions from açai fruit (Euterpe oleracea Mart.)

Anthocyanins are among the most important and widely consumed natural pigments in foods, and have attracted increased attention as natural food colourants and potent bioactive agents. However, anthocyanins are generally unstable and may undergo chemical changes that include oxidative and polymerisation reactions during processing and storage. The role of anthocyanin polymerisation reactions on in vitro intestinal absorption and anti-cancer properties has not been assessed. This study investigated the chemical composition, antioxidant properties, antiproliferative activity, and in vitro absorption of monomeric and polymeric anthocyanin fractions from açai fruit (Euterpe oleracea Mart.). Cyanidin-3-rutinoside (58.5 ± 4.6%) and cyanidin-3-glucoside (41.5 ± 1.1%) were the predominant compounds found in monomeric fractions, while a mixture of anthocyanin adducts were found in polymeric fractions and characterised using HPLC–ESI-MSⁿ analyses. Monomeric fractions (0.5–100 μg cyanidin-3-glucoside equivalents/ml) inhibited HT-29 colon cancer cell proliferation by up to 95.2% while polymeric anthocyanin fractions (0.5–100 μg cyanidin-3-glucoside equivalents/ml) induced up to 92.3% inhibition. In vitro absorption trials using Caco-2 intestinal cell monolayers demonstrated that cyanidin-3-glucoside and cyanidin-3-rutinoside were similarly transported from the apical to the basolateral side of the cell monolayers (0.5–4.9% efficiency), while no polymeric anthocyanins were transported following incubation for up to 2 h. The addition of polymeric anthocyanin fractions also decreased monomeric anthocyanin transport by up to 40.3 ± 2.8%. Results from this study provide novel information regarding the relative size, absorption, and bioactive properties of anthocyanin monomers and polymer adducts.