CAROTENOIDS IN BIOLOGICAL EMULSIONS - SOLUBILITY, SURFACE-TO-CORE DISTRIBUTION, AND RELEASE FROM LIPID DROPLETS

Data on the physico-chemical properties of carotenoids in biological e mulsions are essential to our knowledge of carotenoid metabolism. Ther efore, we determined the behavior of carotenoids in phospholipid-stabi lized triglyceride emulsions, a model for biological emulsions such as dietary emulsions, triglyccride-rich lipoproteins, and intracellular storage droplets. The solubility of beta-carotene (a model for apolar carotenoids, carotenes) in pure bulk triglycerides (0.112 to 0.141 wt % according to triglycerides) was significantly higher than zeaxanthin (a model for polar carotenoids, xanthophylls) (0.022 to 0.088 wt %). The solubility of both carotenoids increased when the chain-length of the triglycerides' fatty acids decreased. The amount of zeaxanthin ass ociated with lipid droplet dramatically increased in phospholipid-trig lyceride droplets as compared to the pure corresponding triglyceride d roplets, whereas the amount of beta-calotene associated with lipid dro plets increased only slightly. beta-carotene distributed almost exclus ively in the core of triolein-lecithin-carotenoid droplets, while zeax anthin distributed preferentially at the droplet's surface. A signific ant percentage (8.3%) of zeaxanthin was spontaneously transferred from lipid droplets to aqueous phase and the remaining part was transferre d during triglyceride hydrolysis catalysed by pancreatic lipase, while beta-carotene absolutely required triglyceride lipolysis to be transf erred to the aque-ous phase. Our results show that polar and apolar ca rotenoids behave differently in biological emulsions. They further our understanding of the bioavailability of polar and apolar carotenoids and of their distribution between lipoprotein particles.