Hydrolysis of the oil phase of a W/O/W emulsion by pancreatic lipase.

W/O/W emulsions are expected to protect bioactive substances from degradation by pancreatic enzymes. We investigated the enzymatic hydrolysis of the oil phase and release of a marker substance from the inner-aqueous phase to the outer-aqueous phase using an artificial digestive fluid. Octanoic acid triacylglycerol (C8TG) was used as the oil phase. W/O/W emulsions were prepared by two-step homogenization and succeeding membrane filtration. When the artificial digestive fluid containing lipase and gall was added to the emulsion, release of the marker substance from the inner-phase solution, oil-phase hydrolysis, and emulsion coalescence occurred in that order. When a coarse emulsion and 0.2- and 0.8-microm membrane-filtered fine emulsions were treated with the fluid for 1 h, the degrees of C8TG hydrolysis were 3.8%, 55% and 57%, the fractions of the marker substance released from the inner-water phase were 2.7%, 89% and 72%, and the median diameters of the oil droplets were changed from 32 to 23 microm, 0.71 to 27 microm, and from 2.2 to 26 microm, respectively. These results suggested that the diameter of the oil droplets in the W/O/W emulsion significantly affected the release profile of the marker loaded in the inner-water phase of the emulsion.