Divalent minerals decrease micellarization and uptake of carotenoids and digestion products into caco-2 cells

Carotenoids are lipophilic, dietary antioxidants with the potential to prevent chronic and age-related diseases. Prior to their availability for physiological functions, carotenoids require micellarization and intestinal uptake, both constituting marginally understood processes. Based on an in vitro digestion model coupled to Caco-2 cells, we assessed the effect of dietary abundant divalent ions on spinach-derived carotenoid micellarization and cellular uptake: Ca and Mg ranging from 7.5 to 25 mmol/L in the digesta and Zn and Fe ranging from 3.8 to 12.5 mmol/L. Both micellarization and uptake were significantly inhibited by minerals in a concentration-dependent manner, with stronger effects for Fe and Zn compared to Ca and Mg. Compared to controls (no mineral addition), fractional micellarization and uptake were decreased to the greatest extent (to 22.5 and 5.0%, respectively; P< 0.001) by 12.5 mmol/L Fe. Effects of Mg were of the least magnitude; at 25 mmol/L, only uptake was decreased significantly to 69.2% of the control value (P< 0.001). Total cellular carotenoid uptake from test meals decreased similarly compared to micellarization; however, decreased β-carotene micellarization was counterbalanced by improved fractional cellular uptakes from the micelles for all ions. Compared to controls, fractional β-carotene uptake from the micelles was greater in samples digested in the presence of Fe, Ca, and Zn, by up to 5-10 times at the highest concentrations of each ion (P< 0.001). Like for the above carotenoids, a high cellular uptake of the epoxycarotenoid conversion products neochrome (from neoxanthin) and luteoxanthin+auroxanthin (from violaxanthin) was also observed. The present results indicate that divalent ions may inhibit carotenoid micellarization and uptake.