Changes in WPI-Stabilized Emulsion Interfacial Properties in Relation to Lipolysis and ß-Carotene Transfer During Exposure to Simulated Gastric–Duodenal Fluids of Variable Composition

Abstract

A whey protein isolate-stabilized oil-in-water emulsion was investigated as a carrier for β-carotene (BC). The changes in emulsion structure during gastric and upper intestinal digestion and BC transfer to the mixed bile salt micelles were studied using a comprehensive in vitro procedure which included colipase (COL), phospholipids (PL), and phospholipase A2 (PLA2), in addition to the standard enzymes and bile salts (BS). During the gastric phase, peptic hydrolysis of the proteins adsorbed at the interface resulted in droplet destabilization. Changes in droplet size distribution continued in the duodenal phase, in the presence of BS alone or BS and PL (BS-PL). Marked influences of BS, COL, PL, and PLA2 on pancreatic triglycerides lipase (PTL) activity were observed. While both BS and PL inhibited PTL activity, the presence of COL and PLA2 minimized the inhibition by BS and PL, respectively. The optimal PTL activity (72.3 ± 1.7% lipid hydrolysis) was only achievable with the inclusion of COL and PLA2, although these components are rarely included in in vitro digestion models. The efficiency of BC micellization was 31.2 ± 1.1% in the presence of only BS and no significant differences were observed in the case of the BS-PL or BS-PL-COL systems (p > 0.05). However, more BC was micellarized (48.5 ± 0.9%) in the presence of BS-PL-COL-PLA2 (p < 0.05). The extent of BC micellarized was linearly proportional to the extent of lipid hydrolysis. These results contribute to an understanding of how emulsions can be used to encapsulate and deliver lipophilic bioactive molecules. Furthermore, they underscore the importance of using physiologically relevant in vitro models to study lipid hydrolysis and the release and transfer of encapsulated molecules.