Comparative behavior of protein or polysaccharide stabilized emulsion under in vitro gastrointestinal conditions

Abstract

In the present work, an in vitro model digestion was used to compare the behavior of emulsions stabilized by proteins or polysaccharide upon digestion and to analyze its relationship with the kinetics and extent of lipid digestion. Oil/water emulsions were prepared using different emulsifiers (β-lactoglobulin, soy protein isolate and hydroxypropylmethylcellulose (HPMC)). The emulsion digestion was carried out in two continuous stages at 37 °C: 1) under simulated gastric conditions (1 h) using pepsin and phosphatidylcholine (simulated gastric fluid: pH 2.5, NaCl, NaH2PO4, KCl and CaCl2) and 2) under simulated intestinal conditions (1 h) with bile salts, pancreatic lipase, trypsin and chymotrypsin (simulated intestinal fluid: pH 7.0, K2HPO4, NaCl and CaCl2). The changes in the particle size distributions, the interfacial area and their microstructures were analyzed as a function of the digestion time. The free fatty acid release during the simulated intestinal stage was also determined and an empirical model was fitted to estimate different kinetic parameters. Irrespective of the composition/structure of emulsions, the initial surface area was found to determine the initial rate of lipolysis. Soy protein was the protein that forms the most resistant emulsion to digestion, showing a degree of free fatty acid release similar to HPMC, which is a non digestible emulsifier. The results are discussed on the basis of the role of bile salts and its effect on oil/water interfaces.