In vitro gastric digestion of heat-induced aggregates of β-lactoglobulin.

In vitro gastric digestion of heat-induced aggregates of β-lactoglobulin (β-LG) in simulated gastric fluid was investigated using sodium dodecyl sulfate-PAGE (under nonreducing and reducing conditions), native PAGE, 2-dimensional electrophoresis, and size exclusion chromatography. Heating at 90°C significantly increased the digestibility of β-LG, with a high initial digestion rate followed by a relatively constant rate of digestion at a high enzyme:substrate (E:S) ratio of 3:1. At a low E:S ratio (1:6), the rate of digestion of β-LG was slower, and intermediate- and low-molecular-weight species could be seen. The high-molecular-weight nonnative aggregates (e.g., pentamers, tetramers, and trimers) were digested relatively rapidly, whereas some of the nonnative dimers were resistant to digestion and others were digested rapidly. The intermediate-molecular-weight species (21 to 23 kDa) were digested slowly. The digestibility of nonnative β-LG aggregates varied significantly depending on the E:S ratio and the types of aggregate. Further investigation is necessary to identify and characterize slowly digested dimers and species of intermediate molecular weight.