Colloidal aspects of protein digestion

The increase in food related health issues has sparked an interest in research on the digestion processes of the gastrointestinal tract. Because of the difficulty and expense of undertaking human trials or even animal experiments, much of the current research uses in vitro models that simulate various aspects of digestion. The results of this research indicate that the rate and extent of protein digestion is governed by accessibility of the cleavage sites to enzymes and local flexibility of the substrate molecule. However, results have also shown that digestion of an allergenic protein to small fragments does not necessarily mean that it will no longer be immunologically active. Other factors are also important. For example, adsorption to an interface increased rates of digestion as did the presence of bile acids. In fact, interaction with a range of physiological surfactants has been shown to be extremely important in protein digestion. When protein is adsorbed to an emulsified food it can be displaced by the surfactants in either the stomach or the small intestine. Lipid interaction with the protein in solution has been demonstrated to be important in effecting rates of proteolysis and phospholipids in particular have provided a protective effect for some milk proteins. Conversely the presence of specific proteins has been shown to affect rates of lipid digestion. The number of such colloidal interactions that we now know may play a role in protein digestion highlights the importance of this area to understanding how we can produce food that optimises nutrition for the consumer.