Adding neutral or anionic hydrocolloids to dairy proteins under in vitro gastric digestion conditions

Abstract

The effect of adding uncharged polysaccharides such as konjac glucomannan (KGM) or negatively charged polysaccharides such as alginate to dairy protein ingredients – milk, whey proteins and calcium caseinate – was investigated through simulated in vitro gastric digestion. The apparent viscosity, microstructure (light microscopy), particle size distribution and degradation (SDS-PAGE) of the proteins were monitored after different in vitro gastric digestion times (0, 30, 60 and 120 min). The addition of KGM increased the viscosity values of the samples during gastric digestion, which probably would increase gastric distention affecting satiety. The microstructure and particle size distribution results showed that the aggregates formed in the dairy protein-konjac glucomannan mixtures at the start of gastric digestion were broken down into smaller ones over time. However, the aggregates formed with the addition of alginate were larger and remained almost unchanged throughout gastric digestion, due to the strong interaction between the opposite charges of the protein and alginate. The SDS-PAGE results showed that whey proteins were more resistant to pepsin digestion than caseins and that the alginate slowed down protein degradation. These findings suggest that a combination of whey proteins and alginate could be used to delay gastric emptying and promote satiety.