In order to test a gingerbread biscuit solution for the presence of starch sugar you should do a chemical test. Starch is not sweet and does not dissolve well in water.
A chemical test for starch includes adding iodine solution (red) and see if it turns blue/black in colour.
Testing proteins on the other hand includes adding Biuret reagent. This turns a mauve or purple colour when mixed with protein.
