Role of calcium and calcium-binding agents on the lipase digestibility of emulsified lipids using an in vitro digestion model

Controlling the digestibility of lipids within the gastrointestinal tract is important for developing food and pharmaceutical products. In vitro digestion methods are commonly used to study the influence of formulation composition and microstructure on lipid digestibility. In this paper, we focus on the impact of calcium and calcium-binding agents on the rate of lipid droplet digestion in corn oil-in-water emulsions monitored using a pH-stat method. The rate of fatty acid production increased with increasing calcium, e.g., the free fatty acids released after 20 min digestion was <12% for 0 mM CaCl2, but >95% for 20 mM CaCl2. The ability of calcium to increase the digestion rate was found for three different emulsifiers used to stabilize the initial lipid droplets: lyso-lecithin, caseinate and β-lactoglobulin. For these three systems, the initial rate of lipid digestion increased in the following order lyso-lecithin > β-lactoglobulin > caseinate at both 0 and 20 mM CaCl2, but the rate was considerably faster at higher calcium levels for all systems. The addition of EDTA, a calcium chelating agent, to emulsions containing 20 mM CaCl2 caused an appreciable decrease in lipid digestion rate, reducing the amount of free fatty acids produced after 20 min from around 97% to 32% when the EDTA level was increased from 0 to 5 mM. Finally, we examined the impact of two anionic polysaccharides (pectin and alginate) on the rate of lipid digestion in emulsions containing 20 mM CaCl2. High methoxy pectin, which does not bind calcium strongly, did not have a major effect on the rate of digestion, whereas alginate, which does bind calcium strongly, depressed the rate considerably. This study has important implications for designing and testing delivery systems that control lipid digestion.