What experience can prove that gastric juice digests proteins only in an acidic environment?

Gastric juice itself has an acid pH. If you bring the pH to neutral or alkaline, that is, more than 6 – the digestion of proteins will already stop. The experience proving that gastric juice breaks down (digests) proteins only in an acidic environment consists in dissolving flakes of half-boiled chicken egg protein, with the addition of natural gastric juice.
Under the action of the enzyme of gastric juice – pepsin – protein molecules break down into simpler compounds, and pepsin acts only in an acidic environment, so the release of hydrochloric acid is a necessary condition for the digestion process.

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