In food, friction, stirring or changes in temperature, and even exposure to oxygen or light, cause its molecules to change their structure. We appreciate it through changes in the color, taste, smell, or texture of food products.
Laura González, head of Nutrition and Health at Nestlé, points out from “El Sisturí” that food is also chemical compound that can vary depending on temperature, friction or interaction with other elements.
What is the chemical basis for color change when cooking food?
It is due to reactions in which mainly carbohydrates participate. They are called caramelization reactions, as occurs with sugar when heated to high temperatures, or when a battered food is fried when starches react with proteins due to the effect of heat.
The texture also changes when we bake or fry a food, because it creates a crispy crust. This crust tends to soften as the food cools because the water, which is retained inside and which is responsible for the juiciness, both in the case of bread, and in baked or fried meats soaks the crunchy outer layer.
Why do some fruits and vegetables darken when cut?
This darkening that occurs, for example, in apple, artichoke or thistle, is the opposite of that caused by darkening due to caramelization. When we cut fruits or vegetables, what we do is break the plant cells and put highly reactive components in contact with other compounds.
We generate substances of brown color in the presence of oxygen. The tendency for this browning to occur depends on whether or not the plant contains substances that react in the presence of oxygen in the air. This occurs for example in bananas, apples, peaches, artichokes, avocados …
To prevent the brown color in fruits and vegetables, the most used action is an acid that in practice is usually lemon or vinegar. By adding this acid, we block the enzymes responsible for this browning.
Why do fats go rancid?
They are produced by the reaction that these fats, especially the unsaturated type, have with oxygen and light. They generate a musty smell and a very characteristic yellowish color. These changes are due to the fact that the fatty acid structures break down and give rise to smaller compounds that are volatile that react with each other and group together into new structures and generate these yellowish pigments.
The more unsaturated the fat, that is, everything that is oils that come from seeds, nut oils, and the foods that contain them, the more likely these types of reactions and changes are to occur.
The acidity of olive oil is a quality parameter. The less acidic, the less likelihood of rancidity.
Long cooking at high temperatures toughens meats because they are subjected to a loss of water. While the maceration with spices, for example, causes the breakdown of part of the proteins and this makes the meat more tender and softer.
However, the quality of the meat and the type of cut also influences the texture. The higher the amount of collagen, the less tender a grilled meat will be. Meats will be more tender if they are cooked over medium heat for a long time.
What is the explained
chemical reaction of foaming during frying?
The presence of foam in the frying oil occurs due to the breakdown of the fat components due to high temperatures among other smaller ones that increase the viscosity of the oil, producing this foam by trapping air bubbles.
When you are frying breaded foods, in which eggs have been used, the proteins and other substances in the egg trap the air and cause the oil to foam. This foam makes it difficult for the heat to transition into the food and makes it soak up more oil.
To avoid it, it is advisable to control the temperature to no more than 200 degrees, keep the oil clean of impurities, and seal the egg well in the breaded. In traditional practice, adding a piece of bread to lemon oil or rind could make it difficult to create foams. But without a doubt the key is in the temperature and the quality of the oil.