Control of lipase digestibility of emulsified lipids by encapsulation within calcium alginate beads

Structured delivery systems, fabricated from natural lipids and polymers, are finding increasing use to improve the oral bioavailability of poorly water-soluble drugs and nutraceuticals, as well as to control the release of lipophilic bioactive molecules within the human gastrointestinal tract. This study focused on the development of filled hydrogel particles to control the digestion and release of encapsulated lipids. These filled hydrogel particles were fabricated by trapping sub-micron lipid droplets within calcium alginate beads. These particles remained intact when the pH was varied from 1 to 7, but exhibited some shrinkage at pH 1 and 2. The free fatty acids released from the filled hydrogel particles after addition of pancreatic lipase were monitored using a pH-stat in vitro digestion model. Encapsulation of lipid droplets within calcium alginate beads (d = 2.4 mm) reduced the free fatty acids released from around 100% to less than 12% after 120 min. The rate and extent of lipid digestion increased with decreasing bead size (from 3.4 to 0.8 mm), decreasing degree of cross-linking (i.e., lower calcium or alginate concentrations), and decreasing triglyceride molecular weight (i.e., tributyrin > MCT ≈ corn oil). These results have important implications for the design of delivery systems to protect and release lipophilic bioactive components within the human body, as well as to modulate satiety/satiation by controlling the rate of lipid digestibility.