why should ketoses not react with benedict's reagent
Benedict's reagent Generally, Benedict's test detects the presence of aldehydes and alpha-hydroxy-ketones, also by hemiacetal, including those that occur in certain ketoses. Thus, although the ketose fructose is not strictly a reducing sugar, it is an alpha-hydroxy-ketone, and gives a positive test because it is converted to the aldoses glucose and mannose by the base in the reagent.
Gastric acid The highly acidic environment in the stomach lumen causes proteins from food to lose their characteristic folded structure (or denature). This exposes the protein's peptide bonds. The gastric chief cells of the stomach secrete enzymes for protein breakdown (inactive pepsinogen, and in infancy rennin). Hydrochloric acid activates pepsinogen into the enzyme pepsin, which then helps digestion by breaking the bonds linking amino acids, a process known as proteolysis. In addition, many microorganisms have their growth inhibited by such an acidic environment, which is helpful to prevent infection.