One of the most entrenched food myths in popular culture assumes that freezing causes the loss of nutrients and other properties, but nothing could be further from the truth. To understand it better it is necessary to know what the freezing process really consists of. As Dr. Elena Aguilar Aguilar, dietician-nutritionist and Member of the Professional College of Dietitians-Nutritionists of Madrid explains, “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 ”. In other words, when freezing a food, the only thing we are doing is inhibiting the reactions of microorganisms and, consequently, extending its useful life.
If the freezing process is carried out correctly, the food does not lose nutrients. What’s more, “there are studies that show the opposite, and that just a few days without freezing are enough for some very important nutrients to be lost. So if a food is not going to be eaten immediately, it is better to freeze it than simply refrigerate it ”, tells us Luis Jiménez, chemist and scientific communicator. A study that compared the losses of some essential vitamins in different fruits and vegetables fresh, stored for five days in the refrigerator or frozen did not find large disparities between the three storage methods. Furthermore, in the cases in which significant differences were recorded, it was observed that foods stored for several days in the refrigerator lost more nutrients than frozen foods. This work was published in 2017 in the Journal of Food Composition and Analysis .
In reality, changes in the composition of food occur especially when preparing it. This is indicated by a review published in 2015 in the 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 to freeze properly
Ultimately, the really important thing is 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 preserve. “First of all, the type of food that is being frozen must be taken into account, since depending on its composition, the final texture may appear softened or hardened as it is damaged due to the effect of ice crystals on cell walls. It is the clear example of potatoes or pasta. Other foods, such as fresh eggs, cannot bear freezing, ”explains Dr. Aguilar.
The product, once cooked, must be quickly cooled and then frozen , in this way the food is being kept as stable as possible, explains Marian Alonso-Cortés, dietitian-nutritionist and head of training at Aizea. It is also important to freeze in hermetic containers and if possible in small portions, to be able to defrost according to the needs of the moment.
With regard to freezing time, this is highly variable depending on the type of freezer and also 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 due to the freezing process itself, but because it is not carried out properly. A study published in 1997 in the European Journal of Cancer Prevention showed how fluctuations in the temperature inside the freezer caused significant losses of vitamins in the products stored in it, especially in meats. This study also analyzed the effects of storage time on food: meats kept in the freezer for long periods experienced large 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 no less important. “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”, explains Dr. Aguilar. So we must 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 directly into the microwave if the bull has ‘caught us’. The most dangerous thing would be to leave it at room temperature ”, indicates Marian Alonso-Cortés.
“Some foods, such as chopped and minced meats, are more susceptible to microbial contamination and, therefore, their freeze-thaw process must be more careful. It is recommended that defrosted foods be used within a maximum of 24 hours ”, concludes Dr. Aguilar.
Advisors: Elena Aguilar Aguilar, dietitian-nutritionist and Member of the Professional College of Dietitians-Nutritionists of Madrid; Luis Jiménez, chemist and scientific communicator, author of the blog What science says to lose weight, Marian Alonso-Cortés, dietician – nutritionist, food technologist and head of the technical department at Aizea , Consultancy in Nutrition and Health.
References:
Devi, R. 2015. Food Processing and Impact on Nutrition. Sch J Agric Vet Sci 2(4A):304-311.
Li et al. 2017. Selected nutrient analyses of fresh, fresh-stored, and frozen fruits and vegetables. Journal of Food Composition and Analysis 59 (8-17)
Severi, S. et al. 1997. Effects of cooking and storage methods on the micronutrient content of foods. Eur J Cancer Prev. Mar;6 Suppl 1:S21-4.
