Carotenoid-enriched oil-in-water emulsions with different droplet sizes (small: d 0.72μm; medium: d 1.9μm; large: d 15.1μm) were subjected to simulated gastrointestinal conditions. The kinetics of lipolysis, micelle formation and carotenoid bioaccessibility were monitored during the intestinal phase. The rates of all three processes increased with decreasing droplet size. The large droplet size emulsion contained undigested oil at the end of digestion, whereas an almost complete hydrolysis was observed for the other two emulsions. The sub-micron emulsion presented a higher conversion of MAGs to FFAs during digestion, which led to a higher concentration of FFAs in the mixed micelles. The incorporation of carotenoids into mixed micelles occurred faster and reached a higher final value for the small droplet size emulsion, leading to final carotenoids bioaccessibility values of around 70%. This work provides valuable information for developing in silico models to simulate the lipid digestibility and carotenoid bioaccessibility.

Highlights:  Citrus pectin is a surface-active molecule  Addition of citrus pectin allows creation of emulsions with small droplet sizes  Pectin structure influences its organization at the oil droplet surface  Emulsion acidity determines the way pectin stabilizes the oil droplet interface  Combination of pectin and conventional emulsifier led to depletion flocculation

Oil-in-water emulsions were prepared with carrot- or tomato-enriched olive oil (5%w/v) and stabilized with Tween80 or sucrose esters (0.5%w/v) with different hydrophilic-lipophilic balance (8; 11 or 16). All emulsions had similar initial oil droplet sizes and were submitted to simulated gastrointestinal conditions using a kinetic digestion procedure. Sucrose esters induced an unstable system after gastric conditions leading to coalesced oil droplets, while Tween80 emulsions remained stable. Emulsion particle sizes at the end of the gastric phase were directly associated with the lipolysis kinetics during the intestinal phase. Moreover, a direct relationship was observed between lipolysis and carotenoid micellarisation for all emulsions, and depended mainly on the surfactant structure used. Tween80 emulsions led to a higher lipolysis extent (53-57%) and carotenoid bioaccessibility (17-42%) compared to sucrose ester emulsions (33-52% and 9-27%, respectively). These findings show the importance of the emulsifier structure and emulsion stability during gastrointestinal conditions in modulating lipolysis kinetics.

Emulsions were prepared with oils (5%w/v) differing in unsaturation degree (olive, soybean or linseed oil) and sucrose ester (0.5%w/v) used as emulsifier. The oils studied were enriched with carotenoids from carrot or tomato purees. All emulsions were in vitro digested and characterised at the level of lipolysis and carotenoid micellarisation kinetics in the small intestinal phase. Olive oil emulsions led to a faster and more extensive lipolysis and carotenoid bioaccessibility compared to soybean and linseed oil emulsions. Monounsaturated fatty acids present in olive oil might be more hydrophobic in comparison to polyunsaturated fatty acids from soybean or linseed oil, leading to micelles with greater capacity of solubilising hydrophobic carotenoids. The obtained results evidence the potential of the oil unsaturation degree for modulating lipolysis and carotenoid bioaccessibility in the gastrointestinal tract and moreover, exemplify the relevance of a kinetic approach including modelling of different lipolysis species to quantitatively prove their interrelation.

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