Tryptone is a water-soluble mixture of peptides formed by the digestion of casein by the enzyme trypsin, while peptone is a water-soluble mixture of polypeptides and amino acids formed by the partial acid or enzymatic hydrolysis of protein. Thus, this is the key difference between tryptone and peptone. Furthermore, tryptone contains oligopeptides, while peptone contains polypeptides and amino acids. But then you can interchange them depending on your the reason you are making use of either on them. I.e Both peptone and tryptone supply nitrogen for bacteria. So, you can use peptone instead of tryptone, Also Both are water-soluble and they are not heat-coagulated . I hope this helps