This depends on the type of enzyme. The enzyme pepsin breaks down proteins in the acidic conditions of the stomach. Pepsin has an optimum of pH 2.5 and a working range of between pH 1-4.

Gastric juice is a liquid produced by the stomach which is essential for breaking down food and absorbing nutrients. It is made up of hydrochloric acid, enzymes (such as pepsin), water and salts.

The new Pepsin Digestibility Rotator from Glas-Col ... It is used for determining indigestible protein from test portions, applicable to all animal proteins.