Nutritional benefits of carotenoids depend on their bioavailability, i.e. the proportion of the carotenoids in food which reaches blood and in fine the target tissue. Since most of carotenoids are lipophilic, their bioavailability strongly depends on their diffusion from the food matrix to a lipid phase inside the stomach. The present study focused on this initial step of the bioavailability called bioaccessibility.
We aimed at quantifying and characterizing the lycopene diffusion from a standard tomato purée to two different lipid containing phases: oil and oil-in-water emulsion.
The partition factor (PF) and the diffusivity (D) of lycopene were defined as follows: PF is the maximum percentage of the initial lycopene which diffuses from the tomato purée to the oil, D is to the slope of the linear part of the kinetic curve. The variation of PF and D were assessed first for various oil/tomato purée ratios and then for oil-in-water emulsion/tomato purée mixtures.
In a mixture of oil/tomato purée 50/50 v/v, maximum transfer of lycopene to the oil was reached after 20 min and PF value calculated was 14.0 ± 0.09%. Varying the percentage of oil from 10 to 90%, PF changed from 7.55% to 30.03% respectively, indicating that even under non limiting conditions (i.e. with a large excess of oil), almost 70% of the lycopene remained in the tomato purée. D calculated from the model was 3.0x10-11 m².s-1 . When oil was replaced by an oil-in-water emulsion, PF remained the same for an equivalent oil-in-water emulsion/tomato purée ratio, and maximum transfer of lycopene to the oil-in-water emulsion was reached after less than 2 minutes. This diffusivity was 2 orders of magnitude below that of sugar from melon to water  and one order of magnitude lower than lutein from Marigold flowers diffusion in hexane .
Times required for the diffusion are compatible with the residence time of the food in the stomach. The fraction of lycopene which is transferred represents possibily all the available lycopene, which could thus exert its antioxidant activity in this compartment of digestion.
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