How much nutrition remains in food after cooking? Are all the vitamins "destroyed" after stir-frying vegetables? Can you get the same amount of calcium from braised pork ribs as from pork rib soup? Some people also say that when eggs are cooked, their protein becomes harder to digest, so it's better to eat them half-cooked. Is that really the case? In fact, the changes that occur in food during cooking are a complex combination of physical and chemical processes. Some nutrients are indeed lost, while others become more easily absorbed by the body. Vitamins are most easily lost:
During cooking, food ingredients can suffer significant vitamin loss due to heat, oxidation, cutting, and other factors. Among these, vitamin C suffers the greatest loss, with B vitamins being lost to a lesser extent, and fat-soluble vitamins having the smallest loss. The approximate order of loss is: C > B1 > B2 > other B vitamins > A > D > E.
Among them, the higher the heating temperature and the longer the cooking time, the greater the loss of vitamin C. Vitamin B1 and B2 are easily soluble in water and stable in acidic solutions, with little loss under normal cooking temperatures. However, they are significantly lost under high heat or when exposed to alkali, so it's best to use less alkali when cooking congee. Vitamin A generally has little loss during normal cooking, but it is easily oxidized when exposed to air, so cooked dishes should be eaten as soon as possible. Vitamin D is heat-resistant and stable to acids and alkalis, with negligible loss during cooking. Vitamin E has high heat resistance and is stable to alkali. Thus, it's clear that not all vitamins are "afraid of heat". For the easily lost vitamin C, it's best to supplement it by eating raw vegetables. Minerals dissolve into the broth:
Minerals include calcium, magnesium, phosphorus, iron, iodine, and more. They are basically not lost during cooking but are simply transferred. This is because when food is heated, it contracts, and the high osmotic pressure environment caused by seasonings and other factors causes these minerals to be lost along with the water into the juices. For example, when boiling bone soup, soluble substances like calcium and phospholipids from the bones dissolve into the broth, so you can get calcium from drinking pork rib soup but not from eating braised pork ribs, because people don't drink the sauce from braised ribs. Similarly, the minerals in vegetables are mostly lost into the cooking water under the high-osmotic environment of salt and soy sauce. Carbohydrates are easier to digest after heating:
Carbohydrates are the most abundant nutrient in grain foods. Sugar and starch, which we eat daily, belong to this category of nutrients. Starch does not dissolve in cold water but will gelatinize when heated in warm or hot water. After gelatinization, starch becomes more viscous and easier to digest. The pectin in vegetables also softens by absorbing water when heated, which is also beneficial for digestion.
Proteins and fats should not be heated for too long: When food proteins are heated, they coagulate. For example, the protein in eggs has the best texture and absorption rate right at the moment of coagulation. If heated for too long, it becomes a hard block. When proteins come into contact with salt, their coagulation is easily promoted. If salt is added too early when cooking beans or stewing meat, the protein on their surface will coagulate, affecting heat transfer to the inside of the ingredients and prolonging the cooking time.
The fat tissues in meat and fish do not undergo qualitative changes during normal cooking. However, excessive heating leads to oxidative decomposition, and the vitamins A and D contained in the fat lose their nutritional value due to this oxidation.
In summary, there are no perfect foods, and no perfect cooking methods. This is because each nutrient has different properties and different influencing factors in digestion and absorption. No matter how you cook, the loss of nutrients is always present, and the best you can do is to minimize it. For healthy individuals, choosing suitable foods and rationally combining them can ensure a basic nutritional balance.
If handled scientifically and reasonably, the loss can be minimized. Specifically, the following methods should be mastered:
1. All ingredients should be washed with cold water, for a short time. Do not soak or rub them for a long time.
2. Follow the principle of washing before cutting. Cutting before washing will cause the loss of water-soluble vitamins and minerals.
3. When the quality of the dishes allows, ingredients should be cut as finely as possible to shorten heating time and help preserve nutrients.
4. Ingredients should be cut and cooked just before use. Avoid keeping them warm or reheating them multiple times, which can reduce the oxidative loss of vitamins.
5. When blanching vegetables or making flour-based foods, try not to add alkali or alkaline substances, as this can avoid significant losses of vitamins, proteins, and minerals.
6. If the flavor permits, add more vinegar. This helps protect vitamins and promotes calcium absorption.
7. For fresh and tender ingredients, rapid cooking over high heat is recommended to shorten the time they spend in the pan, which can effectively reduce the destruction of nutrients by heat.