I suffer from different adverse reactions, stomach-ache, flatulence, nauseas and vomits after particular dishes, like mushrooms, ready-to-eat meals and sauces. What component might cause these symptoms?

Germany

When an adverse reaction to food is observed, the best advice is to consult your doctor to find out the underlying cause. If the cause is a food allergy or food intolerance, a dietician can then help you to find the best diet for you.
Food allergy is a specific adverse reaction to a food or food component that activates the immune system. An allergen (a protein in the offending food, which in the majority of people will not produce an adverse reaction) sets of a chain of reactions in the immune system including the release of antibodies. These antibodies trigger the release of body chemicals, such as histamine, which give rise to various symptoms such as itchy skin, a runny nose, coughing or gastrointestinal problems.
Food intolerance may invoke similar symptoms to a food allergy however the response does not involve the immune system in the same way. Food intolerance occurs when the body can't digest a food or food component properly. While people with true food allergies generally need to eliminate the offending food altogether, people with intolerance can often tolerate small amounts of the food or food component without symptoms.

Also see:

http://www.eufic.org/en/quickfacts/food_allergy.htm

http://www.eufic.org/gb/food/pag/food12/food123.htm