BIOACCESSIBILITY OF LUTEIN INCORPORATED INTO FAT-FREE PROTEIN MATRICES: RELATIONSHIP BETWEEN MICROSTRUCTURE AND IN VITRO STATIC DIGESTION

The bioaccessibility of bioactive compounds depends on their interaction with the other constituents of the food matrix, which makes the incorporation of hydrophobic bioactives into non-fat matrices challenging. In this sense, whey proteins can be useful to microencapsulate and protect these molecules during digestion. The aim of this study was to evaluate the effect of different microstructures of protein-rich matrices on the bioaccessibility of added lutein. High-protein dispersions at pH 7 or 4.5 added with lutein were produced and gelation was induced by heating the dispersions at 90°C for 30 minutes. The dispersions and gels with and without (control) lutein were characterized by color analysis and confocal microscopy, and subsequently submitted to in vitro digestion (INFOGEST 2.0). Protein hydrolysis during digestion was followed by size exclusion chromatography and electrophoresis. The recovery and bioaccessibility of lutein after digestion were also measured. The dispersions and gels produced at pH 4.5 displayed a particulate microstructure, while those at pH 7 had a homogeneous one. After the gastric phase of in vitro digestion, peptides with molecular weight varying from 6.5 to 20 kDa were predominant in the soluble fraction of dispersions, while those with molecular weight < 4.5 kDa were predominant in the soluble fraction of gels. Independently of sample microstructure, bovine serum albumin and α-lactalbumin were degraded in the gastric phase, while β-lactoglobulin was completely degraded only after the intestinal phase. The lutein bioaccessibility varied from 12 to 33 % depending on sample microstructure, and it was greater in gels than in their respective dispersions, in particular at pH 7. Overall, the results point out the ability of gelled protein-rich matrices to protect lutein and increase its bioaccessibility during digestion.