The physicochemical stability and in vitro bioaccessibility of beta-carotene in oil-in-water sodium caseinate emulsions

Beta-carotene (BC), the most important dietary source of provitamin A, is necessary for optimum human health. BC is insoluble or only slightly soluble in most liquids but its bioavailability improves when ingested with fat. Therefore lipid emulsions are ideal matrices for BC delivery. BC (0.1%) in corn oil, the dispersed phase (5 or 10%), was homogenized with 2% sodium caseinate solution in a microfluidizer. Homogenization at different pressures produced droplet diameters (Dz = 368–124 nm) that were linear and inversely related to homogenization pressures in the pressure range 10–100 MPa. Nanoemulsions (r < 200 nm) were prepared at 100 MPa. The sodium caseinate emulsions were generally very stable to coalescence or flocculation over 30 days and the slow rate of volume increase was found to be related to the square of the initial droplet radius following Stokes velocity of settling equation. BC stability towards oxidation was lower as droplet diameter decreased. The extent of lipolysis in an in vitro system was higher and linearly related to the inverse of droplet diameter. Bioaccessibility, as defined by the amount of BC recovered in the aqueous phase after ultracentrifugation, was linearly related to smaller emulsion droplet diameter. These results show that sodium caseinate, a food grade emulsifier, can be used to prepare stable emulsions of food oils carrying beta-carotene. Since food oils facilitate the uptake of beta-carotene this may be a preferred system to deliver beta-carotene.