COOKING WITH EXTRA VIRGIN OLIVE OIL
It’s important to consider how to best use olive oil; crude or in cooking. How can a good olive oil transform a dish?
To make a ‘scientific’ judgment about the dilemma we can refer to two fundamental aspects that characterize the quality of Extra Virgin Olive Oil: nutritional and sensory. Regarding the first aspect, in order to preserve the highest amount of original antioxidants in the finished dish and the lowest amount of thermo-oxidative degradation. With regards to the latter, we should instead ensure the appropriate intensity of scents and aromas to make an exceptionally tasteful dish.
The use of crude Extra Virgin Olive Oil enhances the aspect of ‘food aroma’ and maximizes its bioactive components and benefits. These substances may be lost in part or in whole by cooking, especially if prolonged, or, used with the other ingredients. Using crude Extra Virgin Olive Oil also ensures that it retains the maximum strength of its bitter-peppery character , which tends to be reduced during cooking. There is a strong interaction of bitter phenols within with the oil and other ingredients during cooking, especially if carried out in an aqueous acid, such as tomato juice or in contact with milk or milk products.
While cooking the following occurs:
a) Physical phenomena due to bitter phenols, which migrate from the oil to the aqueous phase, especially if there is a heating system.
b) Chemical phenomena such as the hydrolysis of complex phenols (aglycones), mainly in the acid or during cooking in an aqueous environment, with loss of bitterness.
A specific reaction of certain substances within the oil with other ingredients causes the oil to bond with the milk proteins. On contact with cheese or cottage cheese, the bitter components within the oil will bind stably to the protein component, losing its bitterness. A similar phenomenon occurs with certain peppery or pungent volatile substances present in the oil (aldehydes). A ‘detoxification’ reaction occurs when in contact with the protein matrix. Cooking, therefore, can significantly soften the intensity of an extra virgin olive oil, due to these reactions that occur progressively during the heat treatment. When cooked, does olive oil then, in addition to losing or mitigating its bitter character, also lose its antioxidant properties?
Only in part. Antioxidants together with other ingredients within the oil act as shield against oxygen during cooking and tend to migrate from the oil to the water. In this action the antioxidants present in the oil are modified in a progressive manner and continue to unfold, until exhausted. As a result of cooking, only partial levels of antioxidants are lost. In parallel one can observe an intense interaction between proteins, flavorings and oil phenols (which, as seen above, may be trapped or masked from protein) and a loss of aromas by evaporation or oxidation. Once cooking is completed, one does not identify the fragrant aromas (herbaceous & fruity) of the crude oil but instead an weakened different aroma and, in relation to the type of cooking and ingredients used, a more or less pronounced reduction of sensations which are both bitter and peppery.
Obviously, in cooked foods the final aroma is not the sum of the aromas of the individual raw ingredients. When warm, a myriad of chemical reactions (oxidation, hydrolysis, Maillard reaction, etc) resulting from the different components of food (carbohydrates, protein, oil, etc.) and a new formation of aromas can be noted. At the end of cooking it is not always possible to break down the complex aroma and identify the contribution of each ingredient in the finished product. Everybody knows it: the kitchen is an alchemist’s dream! Moreover the oil with its presence may also contribute to the formation of new aromas, as well as adding its own original aromas. Nevertheless, in prolonged cooking the original intensity of the oil’s aroma is altered by the end of cooking. Extra virgin olive oil has many functions during cooking: as an antioxidant and a source and contributor of new aromas and flavors. In prolonged cooking, however, we lose almost all of the original aromatic fragrances, the herbaceous character, bitter, pungent, the smell of olive oil or extra virgin olive leaf that we perceive in many fresh, crude oils. In particular some of the most aromatic components (esters) are easily lost in cooking.
During cooking, the oil disperses many of its flavors to the other ingredients and in oil-water emulsions, such as some sauces, contributes to the particular viscosity-creaminess of the product. For all these reasons, many use extra virgin olive oil only at the beginning of cooking and then add a little at the end of cooking or even directly onto the serving plate. This often occurs without fully understanding the motivations behind such a choice but simply through instinct or experience. So even if everything depends on the kind of food we are preparing, we can still say that extra virgin olive oil should be used … both crude and during cooking!