A semi dynamic in vitro digestion study of milk protein concentrate dispersions structured with different polysaccharides

Hydrocolloids are often added as functional ingredients in foods, to better design the structure of the matrix and ensure food quality and optimal sensory properties. However, much less is known about their influence on the physical and chemical changes during gastric digestion. In this study, semi-continuous in vitro gastric digestion was applied on a model food system, prepared with milk protein concentrate (MPC) (3% w/v) and 1% alginate, pectin, guar gum, as well as a 1:1 mixture of alginate and pectin. The dynamics during simulated gastric digestion were observed by measuring particle size distributions, structuring at various length scales, as well as by evaluating differences in protein breakdown. Immediately after contact with the simulated gastric fluids, all samples showed extensive aggregation and formation of different structures. MPC control dispersions (no polysaccharide) and MPC containing alginate formed large inhomogeneous aggregates. The lack of structural homogeneity affected the simulated gastric emptying: there were marked differences in the type of aggregates present at various times of emptying depending on the hydrocolloid present in the mixture. MPC containing pectin or guar gum formed macroscopically homogeneous dispersion, with rather small protein aggregates showing a large population of particles between 60 and 100 ​μm of diameter, with marked differences in microstructure. Pectin created large coacervates, while guar microscopic phase separated systems. These dispersions showed a higher extent of protein digestion, due to the larger surface area created for enzyme activity compared to the macroscopically phase separated matrices. In all cases, there was a large undigested fraction at the end point of 140 ​min. SDS PAGE demonstrated differences in the casein peptides distribution depending on the type of polysaccharide present during simulated gastric emptying. This in spite of similarities in cumulative protein emptied. It was concluded that in this semi-continuous in vitro gastric digestion model, structuring with polysaccharides has a significant impact on gastric emptying and protein digestion kinetics.