Do frozen vegetables lose vitamins and minerals?

One of the myths in food more entrenched in popular culture presupposes that freezing causes the loss of nutrients and other properties, but nothing further from reality. To understand it better, it is necessary to know what the freezing process really consists of. As explained by Dr. Elena Aguilar Aguilar, dietitian-nutritionist and Vocal of the Professional Association of Dieticians-Nutritionists of Madrid, "the conservation by freezing causes the formation of ice crystals in the product and, therefore, the decrease in the amount of free water that can be used by the microorganisms present ". That is to say, when freezing a food the only thing that we are doing is to inhibit the reactions of the microorganisms and, consequently, to extend their useful life.

If the freezing process is carried out in a correct way, the food does not lose nutrients. Moreover, "there are studies that show the opposite, and that only a few days without freezing are enough to lose some very important nutrients. So if a food is not going to eat immediately, it is better to freeze it than simply refrigerate it, "says Luis Jiménez, a chemist and scientific disseminator. A study that compared losses of some essential vitamins in different fresh fruits and vegetables, stored five days in the refrigerator or frozen did not find large disparities between the three storage methods. Moreover, in those cases in which significant differences were registered, it was observed that foods stored several days in the refrigerator lost more nutrients than those frozen. This work was published in 2017 in the Journal of Food Composition and Analysis.

Contrary to what popular belief says, if the freezing process is carried out in a correct way, the food does not lose nutrients
Actually, changes in the composition of food are especially given when preparing them. This is indicated by a review published in 2015 in the journal Scholars Journal of Agriculture and Veterinary Sciences: "The nutritional value of a food is preserved when it is frozen. Any loss of nutrients is due to processing before freezing and once the food is thawed. "

Instructions for freezing correctly
What is really important is, in short, to choose the best way to cook the food and then carry out a good process of freezing and thawing the products that we want to keep. "In the first place, we must take into account the type of food that is freezing, since according to its composition the final texture may appear softened or hardened when damaged due to the effect of ice crystals on the cell walls. It is the clear example of potatoes or pasta. Other foods, such as fresh eggs, do not support freezing, "explains Dr. Aguilar.

The most important thing is to choose the best way to cook the food and then carry out a good process of freezing and thawing
The product, once cooked, should be cooled quickly and then frozen, in this way the food is kept as stable as possible, explains Marian Alonso-Cortés, dietitian-nutritionist and head of training in Aizea. It is also important to freeze in airtight containers and, if possible, in small portions, in order to defrost according to the needs of the moment.

With regard to the freezing time, this is very variable depending on the type of freezer and also on the food in question, but in general it is not recommended to store them for more than 6 months. For this it is important to label with date all the products that we freeze.

Actually, the possible losses of nutrients that could occur, are not going to be by the freezing process itself, but because it is not done properly. A study published in 1997 in the European Journal of Cancer Prevention showed how fluctuations in temperature inside the freezer caused significant losses of vitamins in the products stored in the freezer, especially in meat. This study also analyzed the effects of storage time on food: meats stored in the freezer for long periods experienced great losses in thiamine (vitamin B1) and the same happened with ascorbic acid (vitamin C) in fruits and vegetables.

Thawing is key
If freezing is important, thawing is not the least. "In this process there is a reactivation of the microorganisms and spores present and a release of exudate liquid, especially if the initial freezing was not adequate, which carries a high risk of contamination," says Dr. Aguilar. So we should not neglect this phase of the process. "The best way is to take it out the night before and put it in the fridge, or in the microwave directly if you have 'caught the bull'. The most dangerous thing would be to leave it at room temperature, "says Marian Alonso-Cortés.

"Some foods, such as chopped and minced meats, are more susceptible to microbial contamination and, therefore, their freezing-thawing process must be taken care of more. It is recommended that thawed foods be used within 24 hours maximum, "concludes Dr. Aguilar.

Advisors: Elena Aguilar Aguilar, dietitian-nutritionist and Member of the Professional Association of Dieticians-Nutritionists of Madrid; Luis Jiménez, chemist and scientific disseminator, author of the blog What says science to lose weight, Marian Alonso-Cortés, dietitian - nutritionist, food technologist and responsible technical department in Aizea, Nutrition and Health Consulting.