Be aware of how you prepare your Mediterranean food!
Food preparation can influence its nutritional value. Cutting, cooking and other ways in which food is prepared are important factors influencing the release of beneficial substances from food. There are also studies showing an association between the way food is prepared and the effects on health of the Mediterranean diet.
The beneficial effects after the food has been ingested depend on nutrient bioavailability, a term coming from pharmacology and increasingly used by food scientists as well. Bioavailability is defined as the fraction of a nutrient, out of the total ingested, that can carry out its physiological effects into the human body.
Plants contain the so-called “vacuole”, special sub-cellular elements that are broken when the plant is cut for consumption. This favours the release of many bioactive compounds that vacuoles contain. This is also the main reason why washing vegetables after they have been cut instead of before involves a certain loss of nutrients. Among other things, the action of cutting or slicing vegetables allows the release of specific enzymes that can increase nutrient bioavailability, as is the case with the alinase contained in garlic and of myrosinase in crucifers. The substrate of these enzymes is located in a separate cell compartment and the breaking of vegetable cells with slicing makes the enzyme and its substrate meet with each other. The action of these enzymes can be ehnanced by letting your vegetable sit a few minutes after slicing. In the case of fish, on the other hand, slicing or filleting may favour oxidation processes of polyunsaturated fatty acids, a process which in this case is negative.
Other mechanical processes are important in determining the bioavailability of certain nutrients. The lycopene carotene, for example, is contained in tomatoes in a semi-crystalline form; the extensive process undergone by these plants during the preparation of paste and sauces, allows the homogenization of these nutrients and their release from the tomato cells. Tomatoes in the processed form have greater health benefits than raw tomatoes, probably also due to the greater bioavailability of lycopene.
In the Mediterranean cuisine, the consumption of raw vegetables is very common, as is accompanying them with olive oil, which increases the bioavailability of many fat-soluble phytochemical compounds. There are many ways of cooking and preparing food, since these can be fried, grilled, boiled, baked in the oven, marinated, prepared with a filling, or used to prepare pies or soups. Frying with olive oil, in particular, destroys part of its properties. However, the oil does not develop potentially toxic substances, as is the case with other vegetable oils. Frying and grilling also lead to the formation of carcinogenic compounds (polycyclic aromatic hydrocarbons) and, although these are both common cooking techniques in the Mediterranean cuisine, they should be limited, preferring other preparations.
Marinating fish and meat in olive oil is a very common technique, which was originally developed with the aim of softening the meat of animals raised in poor conditions. Marinating with herbs, garlic or onions increases the bioactive compound content of the marinated product. Boiling vegetables in water is a process that involves a substantial loss of nutrients, which are released into the cooking stock. The amount of nutrients lost in this way can also be substantial: 90% of the glucosinolates contained in crucifers can end up in the boiling water. Folates, other B vitamins and vitamin C (which are all heat-sensitive nutrients) can also be lost during cooking. Some food preparation techniques typical of Mediterranean countries, however, ensure that the nutrients released from cooked vegetables are not completely lost. One of these is to reuse the cooking stock of vegetables and legumes for other preparations, such as soups or risottos. Soups in particular are very popular in the Mediterranean cuisine. The addition of a small amount of oil to the stock increases the bioavailability of many nutrients. Using less boiling water also reduces nutrient dispersion. Anyway, cooking can break the cell wall, favouring the release of many bioactive compounds, such as carotenoids. For example, 65% of the carotenoids contained in carrots are absorbed if they are prepared cooked in the form of puree, while only 40% are absorbed when the carrots are consumed raw.
Although many vitamins are heat-sensitive (and therefore it is always good to alternate the consumption of raw and cooked vegetables), glucosinolates, flavonoids and carotenoids are instead stable even when cooked at moderate temperatures. However, also the latter can be destroyed by prolonged cooking at high temperatures. Frying onions for a limited period of time (as is done with fried food) results in a limited loss of nutrients. The presence of fats in general protects the bioactive compounds from degradation, as it happens when preparing a tomato sauce in the presence of oil. Finally, an interesting process takes place during the process of wine production, when some glycosides of the family of the quercetins contained in the grapes are converted to aglycans, which are less soluble. Fortunately, the ethanol that is formed during fermentation can solubilise these compounds and make them more bioavailable. This would explain why flavonoids are more absorbable from wine than from grape juices.
