Micellization of Beta-Carotene from Soy-Protein Stabilized Oil-in-Water Emulsions under In Vitro Conditions of Lipolysis

The details of the interfacial changes occurring during digestion of an oil-in-water emulsion stabilized with soy protein isolate (SPI) and the impact of the changes on lipolysis and subsequent release of beta-carotene (BC) were studied using a two-step in vitro digestion model with varying composition containing bile salts (BS), colipase (COL), phospholipids (PL), and phospholipase A(2) (PLA(2)). The hydrolysis of the interfacial layer by pepsin resulted in significant changes in the emulsion droplet size distribution. The introduction of bio-surfactants (BS and PL), in combination with the release of lipid digestion products in the duodenal stage, resulted in re-emulsification of the oil droplets. During this stage a significant increase in the negative charge of the oil droplets from -40 to -70 mV, was also observed, indicating significant changes in interfacial composition. The activity of the pancreatic triglyceride lipase (PTL), as monitored by the liberation of free fatty acids, was largely governed by the composition of digestive fluids. In the presence of BS alone, lipid hydrolysis reached 66.1 +/- A 3.4%, while addition of PL inhibited lipolysis. Inclusion of PLA(2) was found to increase the rate of lipolysis markedly, and the introduction of COL, along with BS, significantly increased the efficiency of the lipolysis such that a maximum lipid hydrolysis of 81.2 +/- A 1.2% was reached with about 50% transfer of BC to the mixed micelles.