In vitro digestion and beta-carotene delivery of emulsion stabilized by heated WPI and pectin mixture

Abstract

In this study, the impact of a whey protein isolate (WPI) and pectin complex (formed heating the mixture at 85[degrees]C and pH 7) on digestion properties and delivery of [beta]-carotene in oilin-water emulsions was investigated using the in vitro gastric and intestinal models. Beta-Carotene enriched emulsions were stabilized by WPI, heated WPI (HWPI), unheated WPI-pectin mixture (MIX) or heated WPI-pectin mixture (HMIX). As emulsions were digested in the in vitro gastric and intestinal digestions, their droplet size, zeta-potential, microstructure, free fatty acid release and beta-carotene release were measured. Results showed that emulsions stabilized by WPI underwent significant changes during gastric digestion as shown by increased mean droplet sizes and extensive coalescence. These changes have been found to decrease bioaccessibility of beta carotene. The presence of pectin could lead to oil droplet flocculation with much lower extent of coalescence which resulted in decreased beta-carotene release and thus favoring its bioaccessibility during intestinal digestion. Heating of WPI or mixed WPI and pectin also led to decreased coalescence and provided protective effect on beta carotene during gastric digestion. During intestinal digestion, emulsions stabilized by WPI and HWPI completely broke down due to proteolysis while those containing pectin showed better stability due to a more intact interfacial layer structure. Generally, it was found that pectin and heating process favored the stability of emulsion during gastrointestinal digestion overall, which facilitated the digestion of emulsified lipid. However, at the same time, the presence of pectin inhibited the intestinal digestion of lipid by limiting the adsorption of lipase at the interface. Similar effects were observed on the release and bioaccessibility of beta-carotene. A linear relationship was found between beta-carotene bioaccessibility and lipid digestibility. In conclusion, heated WPI and pectin soluble aggregates can be utilized and optimized in designing the delivery and bioaccessibility of lipid and beta carotene.