Monitoring protein hydrolysis by pepsin using pH-stat: In vitro gastric digestions in static and dynamic pH conditions

- It is shown that pepsin activity can be accurately determined using pH-stat at pH ≤ 3.
- This was used to monitor the gastric proteolysis of a model food (Infogest protocol).
- The approach was then extended to a gastric digestion with an acidifying kinetics.
- Degrees of hydrolysis were similar after 2 h of digestion with both protocols.
- The proposed approach is suitable for complex foods, not only protein solutions.

This study intends to demonstrate that acid titration at low pH is very well adapted to the monitoring of pepsin activity. After a description of the underlying principles, this approach was used during in vitro gastric digestions of a model of complex food containing 15 wt% of whey proteins, according to both static (2 h at pH = 3, Infogest protocol) and dynamic pH conditions (from pH 6.3 down to 2 in 1 h). Pepsin activity was quantitatively assessed in all experiments through the calculation of degrees of hydrolysis (DH). Final values of 3.7 and 3.0% were obtained in static and dynamic pH conditions, respectively, and validated using an independent method. Results also show that about 92% of the peptides were detected at pH = 3, and 100% for pH ≤ 2.5. Overall, the proposed approach proved to be very worthy to study protein hydrolysis during in vitro gastric digestions.