Enhancement of phytochemical bioaccessibility from plant-based foods using excipient emulsions: impact of lipid type on carotenoid solubilization from spinach

Effects of lipid type in excipient emulsions on the bioaccessibility of carotenoids (lutein and β-carotene) in spinach were studied using a simulated gastrointestinal tract (GIT). Results showed that the lipid type only had a minor impact on the physical and structural characteristics of the spinach/emulsion mixtures as they passed through simulated mouth, stomach, and small intestine phases. However, a significant effect was observed on lipid digestion, mixed micelle formation, and carotenoid bioaccessibility. Excipient emulsions containing mainly medium chain triacylglycerols (MCTs) (MCT and coconut oils) had faster initial lipid digestion rates, higher overall digestibility, smaller mixed micelle sizes, and higher lutein bioaccessibilities than those containing mainly long chain triacylglycerols (LCTs) (corn, olive, and fish oils). Excipient emulsions rich in long chain monounsaturated fatty acids (MUFAs) (corn and olive oils) formed larger mixed micelles and gave higher β-carotene bioaccessibilities than those rich in either medium chain saturated fatty acids (SFAs) (MCT and coconut oils) or long chain polyunsaturated fatty acids (PUFAs) (fish oil). These differences in bioaccessibility were attributed to differences in micelle size and solubilization capacity, as well as carotenoid dimensions. Finally, emulsions containing a mixed oil phase (MCT oil : corn oil = 1 : 1, w/w) appreciably increased both lutein (from 21% to 42%) and β-carotene (from 6.8% to 25%) bioaccessibility from spinach compared to a control (no oil). These results suggest that mixed LCT–MCT oil phases may be useful for the design of excipient emulsions for improving the bioaccessibility of various hydrophobic nutraceuticals.