Where did vitamins and minerals go? Thermal processing of food and its storage

Thermal processing of food is a topic discussed at every corner, and no wonder. We are not indifferent to what and in what state we eat. Food storage, cooking, freezing and reheating is a daily part of most households. Someone prefers fresh food and doesn't mind standing by the stove even every day. Others have less time and prefer to prepare food in advance for several days, then thaw and reheat it. Even if your domain is rather nearby restaurant than kitchen counter, you might like to know what happens to your meal before you get it served on plate. So that you can better imagine what happens to vitamins and minerals during cooking, how they are in freezer, where you should put eggs and whether you really need to be afraid of microwave, we prepared guide to basic thermal food processing for you.

 

Freezing food

Freezing food is very grateful option for everyone who doesn't have time to cook every day, or for example likes to keep seasonal ingredients for later, to be able to play with various recipes year-round. Although freezing food to make it last longer is very practical, not all products are suitable for it.

Generally frozen food retains its vitamins and minerals and content of its carbohydrates, proteins or fats does not change either. Some types of food have even more beneficial substances after freezing than fresh ones, because they don't have space to lose them due to time. On the other hand, for example vegetables with fine structure, such as lettuce, practically disintegrate during freezing and subsequent thawing. About 90 percent of weight of fruit and vegetables is water. It is retained by solid cells that create structure of fruit and vegetables. So freezing them actually means that we freeze water they contain. And precisely this phenomenon causes disintegration and change of consistency of some types of vegetables or fruit.

According to certain scientific study biggest problem when freezing food is loss of natural color and vitamin C content. Other studies suggest that vitamin C disappears during thawing process, therefore they recommend not to thaw frozen vegetables before use, but add straight to cooking.

 

Miracle called blanching

With vegetables some people are discouraged by extra step needed to be able to freeze it and at same time retain consistency and not turn brown after thawing. This miracle is called blanching. What is it actually? Blanching is special thermal processing of vegetables or fruit, during which foods are first briefly boiled and then immersed in cold water. Even in this case you need to watch out for cooking time, as precisely overcooking can cause loss of nutritional values.

 

Refrigerating food

Refrigerating food is probably most basic thermal food processing or storage we know and use daily. Lifespan of food in fridge is significantly lower than in freezer. What is difference in maintaining nutritional values and vitamins in this case?

With some types of vegetables, for example tomatoes, it is scientifically proven that loss of vitamin C can be prevented, or at least minimized, by keeping at lower temperature than room temperature. For example such tomatoes are suitable to store in fridge instead of kitchen counter or pantry. Certain study showed that when storing small fruit like raspberries, strawberries, cherries or currants in fridge at 4°C content of antioxidants slightly increased compared to room temperature.

Overall it is similar with nutritional values as with freezing. Food in fridge stays fresh and undamaged longer. Proteins, carbohydrates and minerals it contains do not change significantly by storage in fridge. With vitamins however it is according to certain sources little different. They are most sensitive from this point of view. They are often sensitive to air, temperature and even light. Therefore it is generally not recommended to stuff fridge with food of all kinds. Buy what you will eat next days. You will avoid unnecessary throwing away and wasting food.

 

How to properly arrange food in fridge

On bottom shelves it is recommended to store raw meat, fish, dairy products and eggs, because in lower part of fridge temperature is lowest. If your fridge has also drawers for this purpose, it is best to store mentioned foods precisely in them. Drawers help maintain constant temperature and protect products from squeezing, therefore they are suitable also for fruit and vegetables which are fragile. Cooked leftovers, prepared meals and drinks are suitable to place on top shelves. Herbs belong here too.

Fridge door is not suitable for foods that spoil easily, because here temperature is most unstable. You can store here for example drinks or sauces.

Tip - help your fridge

You know it, power outage or fridge malfunctioning and endless stress what will happen to your painstakingly cooked lunches for next days. Tip for emergency mode that can help your cold friend for short time is to store liquids in it. They will keep cold inside fridge during unexpected outage bit longer.

 

Cooking food

Thermal processing of food has its advantages. Cooking food generally improves its digestion and in some cases even increases absorption of many nutrients. For example proteins from boiled eggs are 180 percent better usable than those from thermally unprocessed. Or let's take such carrot, after cooking its structure changes to soft and delicate and at same time more minerals and vitamin C are released when eaten than when eating raw.

Conversely unfavorable effect is formation of carcinogenic substances during too long frying and deep frying. During cooking there is also large loss of vitamins and minerals. For example broccoli and spinach lose up to 50 percent of vitamin C and even larger amount of vitamin B during cooking. Besides that considerable amount of vitamins A, D, E and K or minerals like magnesium, sodium, calcium and potassium are often lost during cooking.

 

Sautéing, steaming and baking

Many of nutrients contained in vegetables are lost primarily by cooking in water. More suitable way of processing, for example broccoli, is therefore to cook it in steam. You can also use method of smaller amount of water and try to cover pot in which you cook vegetables. Another way how to prevent at least certain percentage of nutrient loss like vitamins or thiamine (vitamin B1) is so-called quick sautéing, i.e. brief frying on pan. Good tip is also cutting vegetables into smaller pieces. This way it cooks faster and space for vitamins and minerals to say goodbye forever is reduced. For those of you who like preparing meals in oven, we have good news. During baking only minimal amount of vitamins and minerals is lost, so this way of thermal processing is very suitable.

 

Grilling

Do you know the one about carcinogens in black sausage? Well, unfortunately it is true. During grilling up to 40 percent of B group vitamins disappear from meat and carcinogenic substances are also formed, especially in black spots.

 

Thermal processing of food in microwave

Although microwave is, on one hand ingenious invention, for some people big scarecrow and disappears from households more and more, its advantage regarding nutrient preservation is undeniable. Food is heated in it mostly only really short time and no water is used, so from this point of view it is very gentle to vitamins and minerals contained in food. According to World Health Organization (WHO) one doesn't even have to be afraid of microwave radiation in food.

 

Sources: lifestorage.com, healthline.com, Modern nutrition in fitness and strength sports/Lukáš Roubík
Photo source: Shuttesrtock, Unsplash