Enzymatic degradation and bioaccessibility of protein encapsulated β-carotene nano-emulsions during in vitro gastro-intestinal digestion

Abstract

The aim of this research was to investigate the impact of proteolysis, lipolysis and bile salts on the stability of oil in water emulsions stabilized by proteins and their effect on bioaccessibility of β-carotene in an O/W emulsion system. Nano-emulsions were prepared with whey protein isolate (WPI), soy protein isolate (SPI) and sodium casein (SC) with a microfluidizer under the same operating conditions. The emulsions were characterized by particle size, confocal microscopy, interfacial composition, zeta-potential and digestive properties as a function of time during simulated gastro-intestinal incubation. The WPI-based emulsion was relatively stable in simulated gastric fluid due to the emulsifying activity of β-lactoglobulin, a major component of WPI, while SPI and SC was inclined to aggregate in the presence of pepsin. However, rapid adsorption of lipolysis products and bile salts at the oil-water interfaces for WPI and SC samples sterically hindered the approach of lipase to the lipid core, leading to decreased lipolysis and micellization rates. In the case of SPI-based emulsions, bile salts adsorption and displacement occurred at a lower rate but a higher extent, which provided more surface binding sites for enzymes and accelerated lipolysis. These studies provide information about the relationship between the effects of digestion of the interfacial proteins and the bioaccessibility of lipophilic emulsion contents that could guide the design of safe protein based emulsified bioactive molecular delivery systems.