While peristalsis mashes the food and hydrochloric acid denatures the proteins, other enzymes are responsible for breaking down the food:

Pepsin — the main stomach enzyme that breaks down the protein into smaller particles: peptides and amino acids.
Gastric lipase finishes the work started by the lingual lipase and helps break down the fats.
Gastrin stimulates the production of hydrochloric acid and pepsin. It ensures the acidity level is optimal for food digestion.
Mucin protects the stomach walls from hydrochloric acid.
The intrinsic factor is a protein that protects vitamin B12 from hydrochloric acid and turns it into a form the body can absorb.

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