During cooking, due to increased as well as long temperature effects and using a high amount of water, significant losses of vital substances (micronutrients) occur, with water-soluble vitamins – vitamin C, folic acid, biotin and B vitamins -, sensitive minerals and trace elements – potassium and iodine – as well as natural colors and flavors being transferred to the cooking water. Such losses result from the changes in the food, because the strong and long exposure to heat in the cooking water causes the cell tissue to loosen, the cell walls and proteins to be destroyed, and the starch to gelatinize. The losses increase if the food is placed in the water before boiling and thus exposed to the high temperatures – about 100 °C – for a longer period of time. Under these conditions, vegetables lose 50-75% of B group vitamins [2.1]. Folic acid can be lost by up to 90 % after cooking for as little as two minutes. Particularly sensitive to heat are essential amino acids such as lysine, methionine and valine for protein formation and defense of our immune system, as well as secondary plant compounds such as phytosterols, polyphenols and terpenes in fruits, vegetables and whole grains, which serve on the one hand to add color to foods and on the other hand to our health. If they are destroyed, humans lack these valuable bioactive substances and thus additional protective mechanisms against cancer, free radicals, stress, elevated blood pressure and cholesterol, and immune deficiency. Vegetable oils are often used for cooking, which causes the unsaturated fatty acids in the oils to oxidize because they cannot withstand the heat. They lose their and thus the health-promoting function for our body. If potatoes are overcooked and depleted due to excessive heat, the valuable potato protein loses its biological significance. It is less nutritious for our body and loses essential function. In addition, the cooking process causes at least 30% of the vitamins in the potato to be destroyed. In particular, vitamin C is extremely sensitive to heating and exposure to atmospheric oxygen (oxidation) and is largely destroyed. Furthermore, due to its water solubility, it is flushed out in the cooking water and poured off with the cooking water. Cooking pots made of iron, brass or copper favor the loss of vitamin C, as it is extremely susceptible to contact with heavy metals. Cooking is one of the most commonly used processing methods, resulting in quite a few illnesses from vitamin C deficiency. If the body receives too little of this vitamin, it interferes with the formation of connective tissue and the risk of cancer increases [3.1]. If the leukocytes (white blood cells) have too low a vitamin C content as a result of a deficiency, they can only perform their original function as decisive phagocytes for the body’s own defense system to a limited extent. Daughter tumors, so-called metastases, thus have an easier time spreading and proliferating in the body [3.1]. Vitamin C also has a protective effect against nitrosamines. Due to increased nitrite entry into the body, a lot of nitrite is formed as a result of transformation. This increases the risk of increased release of carcinogenic nitrosamines. Only a small amount of vitamin C in the body does not ensure the inhibitory effect against the dangerous nitrosamines. The risk of developing cancer increases [3.1]. The mineral and trace elements magnesium, calcium and zinc are also relatively sensitive to cooking – in spinach and cauliflower, for example, with losses of 25 to 40 %. In the case of iron, potassium and carotenoids in vegetable products, losses can also be as high as 40 %. In the steaming and steaming processes, food comes into little contact with water and the cooking times are short. The gentle method guarantees that hardly any water-soluble vitamins are leached out. Valuable nutrients and vital substances (macro- and micronutrients) are retained as far as possible.
