Topic 1 Fruits and vegetables: raw and cooked

Fruits and vegetables are plant-based foods that should be present in all our meals.

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Both fruits and vegetables are our main source of several vitamins. In particular, they provide almost all of our vitamin C, much of our folic acid, and at least half of our vitamin A needs. Leaves and other plant parts are also full of antioxidant compounds that give color to many fruits and vegetables. The carotenoid family is an example of these antioxidant compounds so that each type of carotenoid is responsible for a specific color. Chlorophyll in plants, which is responsible for the green color, is also an antioxidant, as are vitamins C and E. Some examples are represented in the following table:

Instead of resorting to vitamin supplements, the important thing is the variety in the consumption of vegetables and fruits following such a simple criterion as the variety of colors. This will ensure a variety that will allow us to benefit more from antioxidants. The intensity of the colour is also important. The more intense a food is, the healthier it will probably be as it will have higher concentrations of the pigment responsible for the colour, which also has antioxidant properties. For example, the leaves of romaine lettuce can contain up to 10 times more lutein and zeaxanthin than the light, tightly packed leaves of iceberg lettuce. Lettuces that form heads keep better than those with loose leaves and in fact iceberg lettuce triumphed in the United States because they were better preserved for storage and transport.

The same thing happens when we compare dark-colored fruits with lighter-colored equivalents. Fruits high in antioxidants are cherries, black grapes, blueberries and strawberries, and among vegetables some examples are garlic, red or yellow onions, green asparagus and beets.

There are fat-soluble vitamins such as vitamins A, D, E and K that are more resistant to the heat and processing that vegetables are subjected to when cooked.

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Salads are an easy dish to prepare and can be a good strategy for introducing raw vegetables. Fruits can also be included. Dressing salads with healthy oils, vinegar, herbs or spices can increase the antioxidant capacity of the dish. Herbs are high in antioxidant and anti-inflammatory compounds. For example, several studies have shown that herbs and spices can lower blood pressure. You have to be creative and there is a lot of variety so you can always find dishes that suit the tastes of the youngest members of the household as well as the rest of the family.

A couple of simple dishes that can be prepared are:

1. Baby spinach, tomato and white cheese salad.

    2. Salads: This video shows 3 simple every salads

Fruits are one of the few natural products that are made to be eaten directly. In fact, this facilitates their reproduction as animals eat the fruit and disperse the seeds inside. The fruits have attractive colours and aromas. Fruits also soften on their own to a tender and juicy consistency. Fruits are therefore generally eaten raw, although they can also be cooked.

Unlike fruits, vegetables maintain a firmer consistency over time and taste too mild (like green beans or potato) or too strong (like onion or garlic). For this reason, vegetables mostly need to be cooked to make them tasty.

The following table shows the maximum loss of vitamins in foods during cooking.

VitaminMaximum loss during cooking (%)
Vitamin A40
Vitamin B6*40
Vitamin B12*10
Vitamin C100
Table DataVitamin D40
Vitamin K5
Niacin75
Riboflavin75
Thiamine80
Folic acid100

Raw tomatoes are high in vitamin C. When they are green they contain a substance, tomatine, which is also in the leaves, which can help to reduce cholesterol. In many supermarkets tomatoes have been harvested when they are green and then the ripening process has been stimulated with ethylene gas, which is why these tomatoes are so tasteless when eaten. For this reason it is best to consume seasonal fruits and vegetables whenever possible.

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Fruits and vegetables lose nutrients and organoleptic characteristics from the moment they are cut. From this moment on they have to use their own vitamins and nutrients to survive. In view of this what we can do is to try to slow down this process of deterioration.

To maintain freshness as long as possible, fruits and vegetables must be protected from 2 powerful enemies: light and heat. Both destroy sensitive vitamins such as B vitamins and vitamin C that are in citrus fruits, peppers, tomatoes, broccoli and leafy vegetables. Root vegetables are more resistant and although local distribution is optimal it is less important in terms of preserving their nutrients.

Delicate vegetables such as tomatoes, asparagus or salad leaves need special protection. These vegetables are more easily damaged and are therefore less resistant to damage during transport. For this reason it is especially recommended to consume local products as they are transported over short distances and can be consumed within a few days after harvesting. When these foods are transported over long distances, they are usually harvested before they ripen in order to protect them better. Root vegetables such as carrots, turnips and radishes are best kept in the refrigerator. Hard leafy vegetables such as kale also keep better. However, there are vegetables such as potatoes, sweet potatoes, onions and pumpkins that are best kept in a cool, dark, well-ventilated cupboard.

The most effective way to extend the shelf life of these fresh products is to control the storage temperature. This temperature depends on where the fruits and vegetables come from. Those from temperate climates are best stored near freezing point. For example, apples. Fruits and vegetables from warmer or tropical climates are damaged at very low temperatures, so it is better to store them at a higher temperature (10 degrees) or even at room temperature. For example, banana skins turn black, avocados darken and stop softening and citrus fruits can develop spots on the skin.

Herbs, such as basil, suffer more in the fridge and keep better if exposed to light. Tomatoes or avocados ripen better outside the fridge and can be stored in the fridge when they are already ripe.

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Freezing is the most effective method of stopping the general metabolism of fruits and vegetables. However, most microbes are revived by heating the vegetable because they are resistant to freezing. Freezing that can be done at home can also spoil the texture and cause vitamins and pigments to be lost. If you are going to freeze vegetables or fruit for a long time it is best to first subject them to a blanching process. This consists of placing them in boiling water for 1-2 minutes and then transferring them to ice water to prevent further cooking and softening of the walls of the vegetable. In this way their texture, colour and properties are better preserved.

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Non-heat techniques are best suited to minimise nutrient loss, such as cured, marinated or pickled foods. It is important to wash raw vegetables thoroughly, but do not soak them because some of the vitamins and minerals will be lost in the water.

You can also make homemade preserves at home. They are very useful to combine it later in different dishes. In these preserves ingredients are introduced to help preserve food for a longer period of time. One method is to use an acidic medium, such as vinegar, which destroys microorganisms and inhibits enzymatic growth. These methods are more like semi-preserves so cold or sterilization is necessary.

Another technique for preserving in fat (confit) can be used for vegetables and also for meat and fish. They are usually sterilized as well.

Benefits of cooking vegetables

Question: Cooked vegetables have always lower nutrient availability compared to raw vegetables.

A) True
B) False

Question: The bioavailability of phenolic compounds is higher in raw tomatoes than in cooked tomatoes.

A) True
B) False

In many instances, cooking of food is necessary to make food safer and to facilitate digestion. Cooking always involves a chemical change in the food and food processing can have beneficial effects by increasing the bioavailability of antioxidant compounds.  It is important to cook as gently as possible, trying to preserve the highest level of nutrients.

The following table shows which foods preserve their nutrients best when eaten raw and which foods preserve their nutrients best when cooked.

Best rawBest stew
Broccoli and watercress: Increased amount of an enzyme responsible for creating anticancer compoundsCarrots: Increased amount of carotenoids
Garlic: Increased amount of an enzyme needed to produce allicin, a healthful compoundSpinach: Better absorption of carotene and iron
Onions: Antioxidant compounds are better preservedCabbage: Increased amount of carotenoids
Peppers: Much higher amount of vitamin CTomatoes: Increased amount of lycopene

Taken from Farrimond S. The science of cooking

Processing vegetables also changes the availability of some of their beneficial compounds. For example, crushing garlic instead of mincing it increases the production of allicin, which is one of the compounds that gives it health-giving properties. Similarly, it is better to finely chop onions. Similarly, chopping cruciferous vegetables, such as broccoli, increases the levels of isothiocyanates, which are bioactive products of glucosinolates.