Amir Malaki Nik

Impact of interfacial composition on emulsion digestion and rate of lipid hydrolysis using different in vitro digestion models.

A sequential in vitro model of digestion was used to investigate the changes in the physicochemical properties of emulsions during gastrointestinal transit. Oil-in-water emulsions were prepared with whey protein isolate (WPI) or soy protein isolate (SPI) at the same protein concentration (1.5%). Despite pepsinolysis of both proteins during the gastric phase, emulsions stabilized with WPI were more stable compared to those prepared with SPI. For both emulsions, the size of the oil droplets, which plays a critical role in lipid digestion, was extensively altered during the duodenal phase due to the presence of bile salts (BS) and phospholipids (PL). As shown by ζ-potential measurements, the results suggested the displacement of both proteins from the interface by BS; however, the displacement was much faster for the WPI-emulsions. The change in interfacial composition of the oil droplets was significantly affected by inclusion of PL and phospholipase A(2) (PLA(2)) in the in vitro digestion model. The interfacial activity of pancreatic triglyceride lipase (PTL) was markedly affected in the presence of the surface-active compounds present in the digestive fluids, including BS, PL, colipase (COL) and PLA(2). A higher percentage of lipid hydrolysis was obtained in the presence of COL and PLA(2) than with BS alone or mixed BS-PL. SPI-emulsions consistently showed a higher degree of lipolysis compared to the WPI-emulsions regardless of the in vitro digestion model used. The results support the conclusion that the interfacial composition of the original emulsion plays a major role in determining the extent of lipolysis.

Surface adsorption alters the susceptibility of whey proteins to pepsin-digestion.

An in vitro digestion model mimicking the gastric phase of the human gastrointestinal tract coupled with SDS-PAGE and MALDI-TOF mass spectroscopy was employed to study the hydrolysis profiles of whey proteins in solution and adsorbed at the oil-water interface. The objective of this work was to understand the differences in hydrolysis behaviour of whey protein isolates once adsorbed at the interface, and comparisons were carried out with pure beta-lactoglobulin and alpha-lactalbumin fractions. In solution, while beta-lactoglobulin appeared to be resistant to enzymatic treatment, alpha-lactalbumin was fully degraded. Adsorption of both proteins at the oil-water interface affected their conformational structure and susceptibility to peptic hydrolysis. Adsorbed beta-lactoglobulin was hydrolyzed into small polypeptides and in contrast, the resistance of alpha-lactalbumin to pepsin increased upon adsorption at the interface. In addition, changes in the particle size distribution of the droplets during pepsin hydrolysis mainly depended on the original protein concentration. The results suggested that exchanges occur at the interface between adsorbed and non-adsorbed protein, that is to say that either some protein desorb from the interface and does not fully recover its structure in solution, or that hydrolysis of the protein at the interface induces further adsorption and hydrolysis of the protein in solution. These mechanisms have important implications in the digestibility of the proteins.

Release of lipophilic molecules during in vitro digestion of soy protein‐stabilized emulsions

SCOPE Solubilization of lipophilic bioactives in gastrointestinal fluids contributes to their bioavailability, but a better understanding of the transfer processes involved and the impact of molecular structure is required. METHODS AND RESULTS The transfer of β-carotene (BC), coenzyme Q10 (CoQ10), vitamin D3 (VitD3), and phytosterols (PSs) from soy protein isolate-stabilized oil-in-water emulsions to the aqueous phase during in vitro digestion was investigated. In the absence of lipolysis, transfer was mainly governed by molecular structure and partitioning within the oil droplets. Less than 3% BC and CoQ10, versus 30.4 ± 0.3% PSs and 24.7 ± 0.4% VitD3, were transferred in this case. However, with lipolysis, PSs and VitD3 rapidly partitioned into the aqueous phase, while lag phases and slower transfer rates were observed for BC and CoQ10. Positive and linear correlations between lipolysis and transfer were observed for all systems. After 2 h exposure to simulated duodenal conditions, there were no differences between percent micellization, except for BC which was proportionally lower. VitD3 and PSs mutually enhanced each others transfer, while no interactions were observed between VitD3 and BC. CONCLUSION Bioactive molecular structure and co-administration influenced the transfer behaviour, with implications for foods designed to optimize health benefits.