It is generally accepted that canned and frozen vegetables and fruits are less nutritious than fresh ones. However, this is not always the case, writes Air force.
It's no secret that sales of canned and frozen foods have grown in recent weeks, and the reason for this is clear - we are trying to stock up on food so as not to go to the store again. Even the sales of freezers have grown.
But we have always been told that fruits and vegetables are most beneficial to eat fresh. Do we harm our health by clogging refrigerators with cans and bags of frozen food?
To correctly answer this question, you must first understand that fruits and vegetables are most nutritious and healthy when they ripen at the time of harvest, emphasizes Fatima Hachem, senior nutrition officer at the Food and Agriculture Organization of the United Nations.
As soon as the apple is plucked from the tree, as soon as the carrot is pulled out of the ground, the process of deterioration of nutritional and energy properties begins, since the main sources of this for an apple or carrot are wood or earth.
“The vegetables we buy to cook have lost some of their nutritional value by the time they hit store shelves,” says Hachem.
After the fruit is picked, it continues to use its own nutrients, breaking down them to maintain cell life.
And some of these substances are especially vulnerable. Vitamin C, for example, which helps the human body absorb iron, lower cholesterol and protect against free radicals, is especially sensitive to the presence of oxygen and light.
Freezing slows down the process of reducing the nutritional value of the product, but the rate at which this nutritional value is lost varies greatly among different fruits and vegetables.
In 2007, Diana Barrett, a former researcher from the University of California, Davis, made an analytical review of numerous scientific papers on the nutritional properties of fresh, frozen, and canned fruits and vegetables.
She found that spinach, for example, loses 100% of its vitamin C after seven days if stored at room temperature at 20 degrees Celsius. When stored in the refrigerator, 75% are lost.
But carrots lose only 27% of vitamin C per week of storage at room temperature.
“Spinach leaves are very thin, they lose more moisture, suffer more from heat rise than the same carrots, which are denser,” says Barrett.
However, all other vegetables, according to Barrett's study, lost significantly less vitamin C reserves after they were frozen - even spinach lost only 30% of this vitamin.
The reason is that freezing slows down the oxidation process, due to which, among other things, vegetables and fruits turn brown after being harvested.
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Frozen food is a relatively recent innovation in the food industry.
Take, for example, frozen green peas. Today, the process of its production (from harvesting, transportation to the factory, washing, cleaning from pods to directly freezing) is only a little more than two hours. It would take days in the 1970s.
“Compare this to fresh vegetables: they are harvested, delivered to a packaging facility, packaged, sorted, taken to sellers - and only then are they available to buyers,” says Richard Harrow, CEO of the British Federation of Frozen Food Producers.
"In 99% of cases, it takes longer than processing and freezing green peas."
You, apparently, already understood that speed is extremely important in the production of frozen products: as soon as the fruit breaks off a tree or digs out of the ground, the race against time begins.
Over the past few decades, technological innovation has dramatically reduced the duration of this process.
The same peas, according to Harrow, undergoes rapid freezing in a metal tray with a grill instead of a bottom, and under the tray, high-speed fans drive up cold air, and thus the peas are, as it were, supported on an air cushion.
After this, the peas are placed in cold storage until the packing time is right. Most vegetables are frozen in the same way.
There is, however, one important caveat. Before freezing, peas are cleaned of pods, during which it is heated to high temperature for several minutes.
This is done in order to deactivate unnecessary enzymes, whose work undesirably affects the appearance of products - its color and texture, Barrett points out.
However, at the same time, heating reduces the nutrient content of the product.
And what about the bank?
However, all these nutritional losses fade in comparison with those that occur with much more intense heating before preserving foods that are intended to be in a metal can, Barrett emphasizes.
But as is the case with fresh vegetables and fruits, for different foods and different vitamins, this happens in different ways, to different degrees.
Barrett found that the main difference exists between foods with water-soluble nutrients (including vitamins C and B) and foods with fat-soluble nutrients (including vitamins A and E).
Her analysis concluded that fresh food is especially good for vitamin C, as it is very sensitive to heat. But - only if the storage time is minimal.
The same products, in which there are more vitamins E and A (for example, canned carrots and tomatoes), with much less loss, tolerate strong heating during processing.
However, canned food has an additional minus: salt (in the case of vegetables) and sugar (in the case of fruits) are added to it.
Nevertheless, for this minus, canned food has its own important plus: they are safer, because the products are sterilized before preservation. The risk of detecting pathogens there is ultimately small, and canned foods can be stored for years.
The rule is the same - five a day
According to Fatima Hachem, the most important thing is to eat varied, alternating between fresh, frozen and canned.
“If we manage to eat a fresh salad at least once a day, combined with meals made from frozen and canned food, then we are not at risk,” she says.
Some experts also advise buying so-called organic products (organic products), grown without the use of pesticides in the area where you live - they are fresh and full of important nutrients.
In the current situation, not everyone can afford to buy fresh organic, farm. But this should not be a barrier to proper nutrition, experts say.
Whether they are frozen, canned or fresh, fruits and vegetables should be eaten every day and do not stop doing this even during a pandemic.
Your goal is the same: daily five servings (for example, two apples, a tomato, and two cucumbers).