According to Colorado State University, hydrochloric acid in the stomach kills any bacteria in food. It both attacks proteins directly and activates the pepsin enzyme, which is even more powerful in breaking down proteins. Springfield Technical Community College notes that the acid is released both on food detection and ingestion.
Colorado State University explains that the stomach secretions, also known as gastric juices, have four major components. One is hydrochloric acid, with the others being mucus, protein-attacking enzymes known as proteases, and hormones. The hormones control both the release of acid and the stomach movements. The stomach also releases a few other substances that help the intestines absorb nutrients later.