HOW TO MAINTAIN FOOD NUTRIENTS

CLEANING, PREPARING AND cooking a nutritious meal can cause the loss of a significant portion of the nutritional properties, but also during storage some foods can change their nutritional content. The environment in which we find foods can have a decisive influence on the amount of nutrients that they offer.

Light affects the nutritional content of food because it promotes the oxidation of fats and some vitamins (C, B2, pro-vitamin A, folic acid).

That is why food such as oils must be protected in opaque containers to prevent rancidity, and why it is recommended that once orange juice is squeezed it is drunk early to avoid the loss of vitamin C.

OXYGEN, DEPENDING ON the length and conditions of storage and distribution, influences the degradation of certain foods, especially vegetables, fresh fruits and potatoes. Vitamin losses of these foods will depend on the duration and storage conditions.

At room temperature vegetables lose between 5-8% of vitamin C in the first 2 hours of picking, and after 24 hours between 40-90% of vitamin C.

However if kept in the refrigerator or in a cool, dry place, vitamin losses are reduced, however a lettuce after 5 days in the refrigerator will have lost between 25 and 50% of vitamin C. Do not forget that vegetables and fruits, once collected, breathe while ripening and secrete ethylene as part of the breathing process.

Root vegetables and tubers have a lower breathing rate and will endure several weeks in the cool, so potatoes stored in a dark place take around three months to lose 50% of vitamin C.

TEMPERATURE PLAYS AN important role in food preservation, but inevitably some of their vitamins and minerals may degrade. As food cools deterioration slows and stops completely when the food is frozen. Moisture and pH of food also influence conservation. For example, humidity promotes mould growth, but by using hermetic packaging this can be avoided. Food stored in an acid medium, such as in cans, is defended from microbial assault.

WHEN PREPARING AND cooking food we produce nutritional losses depend on the care with which the food is protected from light, oxygen, temperature, humidity or pH.

If we leave a peeled potato on a plate and observe it for a few hours, we find that ambient oxygen has oxidized the surface. If we let a potato soak, it does not blacken as it does when in contact with the air but it still oxidizes and loses much of its vitamins.

In general, foods soaked for half an hour loses a significant amount of vitamins, including C, from the action of oxygen in the water. If food is chopped, there will be more surface in contact with oxygen so the oxidation will be faster, as is the case of cut lettuce, which darkens quicker when cut than if the whole leaves are kept clean and dry.

THE SAME HAPPENS when food is ground by introducing oxygen through the action of the mixer; it is recommended to immediately consume fruit or vegetable purees, to ensure the vitamins are not lost. For all these reasons vegetables should be handled and cut just before cooking, avoid prolonged soaking and previous cutting that increase nutrient losses. Also thick peeling of fruits and vegetables (peel very thick) can lead to vitamin loss from under the skin as there are more vitamins in the centre of the fruit. We recommend using the outer parts of the salad because there are more vitamins than inside as the leaves are greener and have more chlorophyll in the head, which comes from sunlight.

We should use the best way of cooking that maintains the nutritional value of each meal, since according to the technique used, nutrition can be enriched (especially if you fry which adds calories) or reduced (mainly minerals and vitamins). Vegetables and tubers are easier to digest cooked, but the heat of cooking destroys some vitamins, especially C, and we lose mineral salts that dissolve in the water.

Therefore, whenever possible, fruit and raw vegetables should take them in the form of salads, or just boiled.

Some vegetables are eaten cooked, because raw they are unpalatable and even toxic, such as aubergines and potatoes (raw they can contain solanine, an alkaloid toxic, especially if they are ripe).

THE BEST WAY to use the nutrition of fruit is eaten raw. If they are eaten without peeling, they should be washed well to remove pesticides that may have accumulated on the surface.

If we are going to cook food in water the best way is to put them into boiling water because it forms a kind of crust that acts as a barrier reducing the loss of vitamins and minerals.

If we put food in cold water and bring it to a boil we lose more protein, vitamins and minerals, as the water does not scald and produce a protective barrier and they spend a large amount of time in the cooking water.

Steamed vegetables retain minerals, and vitamin loss is less than the traditional boiled, since there is no dilution of the nutrients in water. In addition, the food is much tastier and is particularly suitable for people who must restrict salt in their diet.

To make a good soup the best advice is to put all the ingredients in cold water, but if we cook vegetables and are not going to save the cooking broth it is better to steam or place in boiling water.

Adding a few drops of lemon juice or vinegar to the cooking water helps conserve vitamins as they are stored in an acid medium, this same is true for salad after soaking.

Arancha Coromina

Dietitian-Nutritionist

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Posted by editor on 2010-08-18 Filed under August 2010, Food, Help and Advice. You can follow any responses to this entry through the RSS 2.0. You can leave a response or trackback to this entry