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How does heat treatment affect the content of vitamins?


The nutrients in the foods we consume every day are essential for us because they keep our bodies healthy and full of energy.

But have you ever wondered how the nutrient content of foods changes during heat treatment?

Cooking, baking, frying and grilling, all these processes significantly affect the final content of nutrients in our diet and their absorption into the body.

So how does cooking the food change the nutrient content? And which culinary preparation is the best?

Pay attention not only to the content, but also to the absorption

The resulting content of nutrients in the food is very often significantly affected by the way we prepare the food.

The mere combination of two or more foods is considered a kind of “culinary preparation”.

The joint consumption of different raw materials is called food synergy and has a significant effect on nutrient absorption.

For macronutrients, which include sugars, fats and proteins, the effect of heat treatment is visible, for example, on eggs.

Boiled egg protein is 180% more digestible than raw egg protein.

But eggs are an exception to the rule. This is because the absorption of key nutrients usually decreases.

Vitamins and minerals are among the most “endangered” nutrients.

These micronutrients are degraded most often and to the greatest extent during heat treatment.

Vitamins D, E and K are among the most stable micronutrients. These three heroes are the most resistant to heat treatment.

Vitamin C, folic acid and thiamine (vitamin B1), on the other hand, do not last long.

Vitamin C is even prone to freezing compared to others, take a look at our table!

Vitamin losses in various types of processing

Vitamin/MineralFreezingHot air dryingCookingRe-Heating
Vitamin C30%80%50%50%
Vitamin B120%0%45%45%
Vitamin B60%10%50%45%
Vitamin A5%50%25%10%
Folid acid5%50%70%30%
The values ​​given in the table are approximate. It depends on the cooking time, the type of raw material, the water content and other factors.

It is important to combine cooked foods and raw or lyophilized ingredients.

Because, despite the fact that the heat treatment of raw materials improves their digestibility and increases the bioavailability of nutrients, it negatively affects the levels of vitamins and minerals, which does not happen in the lyophilization process.

Try picking dried fruit and nuts next time with lyophilized fruit.

Drying significantly increases the concentration of fiber and minerals, but vitamin C suffers from this process.

Lyophilization, on the other hand, preserves the necessary vitamins, minerals and antioxidants, especially vitamin C, which is destroyed by drying.

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Your snack will therefore be fuller and more vitamin-complex.

How to prepare food

1. Cooking and stewing

Cooking and stewing are similar processes in which water is an indispensable factor.

However, it causes significant losses of vitamin C. Research shows that cooked vegetables have 50% less vitamin C than raw vegetables.

But why is vitamin C lost through cooking? This is due to its solubility in water and sensitivity to heat.

After immersion and subsequent heating of the vegetables, this vitamin spills out of it spontaneously and remains forgotten in the water, which often drains away with kitchen waste.

The same is true for B vitamins. They even lose up to 60%.

But what may surprise you is that vegetable broth retains 100% of its original mineral content and vitamins lose a maximum of one-third.

Cooking and stewing therefore cause a massive flush of water-soluble vitamins.

If you want to avoid these losses, you also need to avoid water.

2. Baking and grilling

Baking and grilling are probably the most popular ways to cook food today.

The compact grill becomes an indispensable helper for every modern household.

However, baking and grilling also have their flies.

The content of B vitamins is reduced by more than 40% through these processes.

This is mainly due to the dripping of juice, which is otherwise very rich in nutrients.

Barbecue is suitable for preparing vegetables and meat, especially in the summer months.

It can be said that, despite the small difficulties, it is the best for maintaining vitamin C.

Many people are also concerned about polycyclic aromatic hydrocarbons, which are formed mainly during grilling and are potentially carcinogenic substances.

However, the researchers found that the content of these hydrocarbons can be reduced by 41-89% if we minimize the smoke to which the food on the grill is exposed and remove excess fat from the raw material before grilling.

3. Frying

Frying is a complicated process that requires a lot of fat and usually takes place at really high temperatures.

What you might not expect is that frying, unlike other culinary treatments, retains more vitamin C and B vitamins.

It can also increase the amount of fiber in potatoes by converting their simple starch to complex starch.

But not all fried gold glitters! Fish meat contains healthy omega-3 fatty acids, which are very mild and therefore prone to damage at high temperatures.

Research has shown that, for example, frying tuna destroys its omega-3 fatty acids, while baking causes minimal losses on these fatty acids. So maybe next time it is better to throw fish in the oven instead of the pan or fryer, and thus preserve as many healthy nutrients as possible!

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In addition, when the oil is heated to a high temperature for a long time, toxic substances are formed – aldehydes, which are associated with an increased risk of cancer and other diseases.

Aldehyde production is also affected by the type of oil used, temperature and frying time. If you still have a fried meal, choose the most suitable oil.

4. Drying and lyophilization

Heat-drying raw materials (such as fruit) can reduce the amount of vitamin C retained, but it can also concentrate other nutrients – especially fiber and antioxidants.

But freeze-drying results in almost no loss of vitamins or minerals! Dehydration of foods also increases their energy density because it reduces their volume.

What about the microwave?

The microwave oven is a great helper for almost every household.

Probably every one of us knows that feeling.

You come home late at night and the last thing you want to do is pick up a wooden spoon and start preparing dinner.

And so it is often the microwave that enters the scene.

If you are afraid that the microwave will spoil your food, you don’t have to have it anymore!

Studies show that using a microwave oven is one of the best methods for keeping antioxidants in your diet, especially those contained in garlic and mushrooms.

The researchers found that when heated in a microwave oven, broccoli and spinach lost only about a third of their vitamin C, unlike cooking in water, where the losses were over 50%!

However, reheating is problematic with a microwave oven. With each new warm-up, valuable vitamins are lost!

But be careful not to heat the food in unsuitable plastic boxes. Some plastics can release harmful substances (BPA and phthalates) due to high temperatures.

Therefore, it is better to heat the food in the microwave in porcelain or glass containers!

10 tips on how to reduce nutrient loss during cooking

  1. Use as little water as possible during cooking to avoid unnecessary loss of vitamin C.
  2. Do not pour out the water in which the food was cooked, but try to use it further. For example, as a broth or sauce.
  3. Serve the juice from the meat that remains in the pan with the meat.
  4. Peel the vegetables only after you have cooked them, for example, in the case of potatoes, they have reduced the loss of vitamin C by almost 20%.
  5. Bake or roast the vegetables, so keep much more vitamin C and B.
  6. Try to consume ready-made food within one to two days so that it does not lose all its remaining vitamin C on contact with the air.
  7. It is better to cut the ingredients until they have been cooked. Cooking foods as a whole results in less loss of vitamins.
  8. Only cook food for as long as necessary.
  9. Use fresh ingredients whenever possible.
  10. Do not use baking soda when cooking vegetables. Soda helps maintain the original color of vegetables, but it destroys vitamin C.
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