Abstract: An in vitro simulated gastrointestinal (GI) digestion system was used to investigate the effects of ratio between casein and whey protein and calcium chloride concentration as well as interaction between the two factors on the digestion of a structured lipid made with 1,3-dioleoyl-2-palmitoylglycerol (OPO). The changes in the release rate of fatty acids, particle size distribution and fatty acid composition were determined during the digestion process. The results showed that at the same emulsifier ratio, lipid bioavailability of OPO emulsions increased with the increase of CaCl2 concentration. At a CaCl2 concentration of 20 mmol/L, the release rate of free fatty acids (FFA) from emulsions stabilized with different ratios between whey protein and casein decreased as follows: 10:0 > 6:4 > 0:10 during simulated gastric digestion. For each CaCl2 concentration, the average particle size of the emulsions became smaller after simulated GI digestion. The d(0.1), d(0.5), and d(0.9) values of the fresh emulsions increased with increasing CaCl2 concentration. Both the release rate and amount of FFA during the simulated intestinal digestion of the three emulsions became greater with increasing CaCl2 concentration. FAA and monoglyceride composition analysis showed that the digested products consisted mainly of palmitic acid and oleic acid. The effect of different calcium salts on the lipid digestion of OPO emulsions was also investigated. It turned out that calcium salts with higher solubility promoted lipid hydrolysis and that the release rate and amount of FFA with different calcium salts during simulated intestinal digestion were ranked in the following order: calcium citrate > calcium chloride > calcium lactate > calcium carbonate.

Key words: 1,3-dioleoyl-2-palmitoylglycerol, emulsion, in vitro digestion, CaCl2