The answer to this question would be: Gastric juices mix with food to partially digest it.
Stomach or gaster will produce gastric juice which has an enzyme to digest protein and also lower the pH into acid. This way the gaster can kill bacteria that digested with the food to protect the intestine and helping digesting a part of the food(mainly protein). The food will be kept in the stomach for 2 hours so it's not quickly moved to the small intestine.
Other digestion will be done by the pancreas which can digest fat, carbohydrate, and protein in the small intestine.