Gastric juice contains HCl,Pepsin, Renin etc.
1.HCl makes the food softer and kills the harmful bacteria.
2. HCl helps to convert inactive pepsinogen into active pepsin and pro renin
into renin and provides appropriate pH for protein digestion.
3. Casein(milk protein) gets converted to paracasein which is further converted to peptones by renin hydrolysis.