Quantitative analysis of surface-located triacylglycerol in intact emulsion particles

The amount of triacylglycerol (TG) in the surface monolayer of intact phosp holipid-stabilized emulsions was determined using C-13 nuclear magnetic res onance (C-13 NMR). C-13 NMR spectra of emulsions composed of bulk long-chai n or medium-chain TG were prepared with [C-13(3)]-carbonyl-enriched triolei n, tripalmitin, or trioctanoin, and were analyzed and compared with NMR spe ctra of phosphatidylcholine vesicles with and without added TG. Identificat ion of carbonyl peaks intermediate between those of phosphatidylcholine car bonyls and bulk. TG confirmed the presence of surface TG in each emulsion. The surface of emulsions contained 2.2 mol % tripalmitin and 1.4 mol re tri olein, but significantly more medium-chain TG, 9.1 mol % trioctanoin, as pr edicted by measurements of TG in phospholipid vesicles. Thus, medium-chain TGs are more accessible than long-chain TGs to enzymes or pro-oxidants in t he continuous phase of phospholipid-stabilized emulsion systems. The quanti tative determination of surface-located TG in intact particles will advance the understanding of emulsion colloidal properties, physicochemical stabil ity, and metabolic behavior.