Amino Acids correction
In many foods items Amino acids(AA) do not adds up to what they should (do not reach its total protein content or it goes beyond its total protein content). So in the algorithm you could make it so that it detect the difference between addition of each AA and total protein then correct by a relative factor all of its AA (evenly). It seems a simple task, mathematically at least.
Sometimes it even did not put the data (eg. Tryptophan and lentils sprouts).
Also make a sign that data is missing (for example a branded product with no AA data might falsely biased calculation for the day).
People might be mistaken that they lack some AA and confirming their inexistant deficiency through your app...
Also, in the summury, the percentage of kcal from protein is often innacurate (lower than real value).