Scent of chemistry

What is “seduce” your nose
Aroma is one of the important sensory characteristics in food. Good aroma quality can make people have pleasant emotions. The aroma of food can stimulate the body’s digestive system through conditional reflex, promote the secretion of saliva and gastric juice, and produce appetite. The scent is smelled by our nose, so the aroma is volatile. Its molecules are scattered in the air and can be felt by stimulating the olfactory cells after entering our nose. Each food has its own unique characteristic flavor. This characteristic flavor is usually not composed of one or several substances, but is composed of dozens or even hundreds of volatile substances in a certain proportion, such as brewing coffee. There are more than 400 kinds of aroma substances, and there are more than 1000 kinds of aroma compounds in liquor, and the composition is very complicated.

Do not look at the variety of aroma substances in food, the content is very low, the content of aroma substances in general food is 10-6 ~ 10-10 of the weight of food. Most aroma substances have poor stability and are susceptible to chemical changes due to environmental factors. In addition, the aroma substances in the food are also susceptible to the concentration, the concentration of the aroma substances is different, and the odor is different. For example, 2-pentylfuran exhibits a licorice flavor at a higher concentration, and after dilution, Has a bean flavor.

There are many kinds of substances that make up the smell of food, both inorganic and organic. Generally speaking, only a small number of inorganic substances such as SO2, NO2, NH3, and H2S have odor, and most inorganic substances have no odor. The volatile organic substances are mostly odorous, and the odor substances in foods are mostly organic substances, mainly including aliphatic hydrocarbon oxygenated derivatives (alcohols, aldehydes, ketones, carboxylic acids, esters, etc.), aromatic compounds, nitrogen-containing compounds, Sulfur-containing compounds, etc. The specific odor of these substances is determined by their molecular structure. For example, low-grade saturated fatty aldehydes, such as formaldehyde, have a strong pungent odor. As their molecular mass increases, the pungent odor weakens and gradually becomes pleasant. Odor; saturated aldehydes with a carbon number between 8 and 12 also have a good aroma at very low concentrations, such as furfural with rose and almond notes, furfural with citrus notes, and dodecyl aldehyde with floral aroma. As the carbon number increases, the odor of the saturated aldehyde gradually decreases.

Although the volatile substances in food are various in variety and complicated in composition, not every volatile substance contributes to the overall aroma of the food, and the aroma substance which contributes to the overall aroma of the food is called an aroma active substance. Some aroma substances are high in content, but they contribute little to the overall aroma. On the contrary, some very small substances contribute a lot to the overall aroma of the food, and its content is difficult to accurately measure even with modern analytical techniques.

Alternative “aroma”
In addition to increasing appetite, the fragrance can help people identify the freshness of the food. The scent in non-fresh or corrupt foods will weaken, odor and even smell, suggesting that food has deteriorated. The “odor” of food is usually caused by the instability of aroma substances in food, or the degradation of certain macromolecular substances, or the growth and reproduction of microorganisms. For example, when orange juice is heated at a high temperature, “cooking” occurs. “Taste”, one of the reasons is that the sulfur-containing amino acid degradation produces sulfur-containing odor substances; soy milk is easy to produce “bean flavor” in the production process, which is due to various linoleic acid, linolenic acid and other unsaturated Fatty acids are oxidized by lipoxygenase to form volatile compounds such as small alcohols, aldehydes, ketones, acids and amines; after the meat is spoiled, there will be “smelly smell”, which is caused by protein degradation, such as methylamine, cadaverine and skatole. Volatile matter.

Hundreds of aromas in coffee

The aroma components in food are complex

Smelly smell, eat incense

Of course, not all odors are unpopular. Some odorous foods are also common on people’s tables. For example, traditional Chinese foods such as stinky tofu and preserved eggs, the stench of stinky tofu is mainly derived from protein degradation. The hydrogen sulphide, hydrazine and other substances produced, the slight odor of preserved eggs is also derived from the degradation products of proteins – hydrogen sulfide and ammonia; the durian known as the “king of fruits”, its odor is from low-carbon esters. Produced by a complex mixture of substances; canned ten times more stinky than stinky tofu, the odor is derived from volatile substances such as acetic acid, propionic acid, butyric acid, hydrogen sulfide, etc. produced during fermentation. The food is so stinking that the Swedish natives also need to use a nose clip to clip the nose.

Add some chemistry to the cooking
We all know that the unbaked dough is not aroma, while the raw meat has a bad smell of meat, but the dough is baked at a high temperature to form a very attractive aroma, while the raw meat is stewed and grilled. It also has a rich flavour of meat.

This wonderful change in food processing and cooking is due to several miraculous chemical and biological reactions. The first is the Maillard reaction. This is a layered reaction of a carbonyl compound (reducing saccharide) and an amino compound (amine, amino acid, peptide, and protein) at a certain temperature to form various flavor substances, and a browning reaction occurs, which is a food color. And one of the main sources of scent, such as freshly baked bread, freshly grilled steak, freshly ground coffee, freshly ground peanuts and so on. The Maillard reaction is a very complex reaction process, and the products produced are also very complex. The products are affected by conditions such as temperature, pH, substrate, water activity, etc., and the Maillard reaction process so far. The products it produces are still unclear.

The Maillard reaction has a major impact on the color and aroma of the meat.

Smelly world famous Swedish salmon canned (Image Source / Wiki)

The enzymatic reaction causes the cut onions to emit a pungent odor

The second is an enzymatic reaction. The aroma precursors produced by many plants and animals during their growth have no odor, but they can generate volatile odorants through various biochemical or chemical routes under the action of enzymes. For example, fruits will form more fatty acids when they are immature, and when they mature, they will produce alcohol, aldehydes and ester aromas under the action of enzymes. Some aroma substances in vegetables are produced by enzymatic reactions after their cells are destroyed. For example, onions, we can’t smell the obvious smell before the cells are destroyed, but after cutting, we can feel very obvious. The pungent smell can even make people cry. The reason is that after the cells are destroyed, sulfur-containing volatile odor substances are generated within a few seconds under the action of alliinase, which can cause tears in the cornea of ​​the human eye.

The third is the thermal degradation reaction. During the heat treatment process, many components of the food will undergo a certain degree of degradation, resulting in a very rich flavor compound. For example, fatty acids in foods can be degraded under high temperature to form volatile aldehydes, ketones, acids and other aroma substances.

The fourth is fermentation. The characteristic aroma of many foods is produced by fermentation, such as alcohol, kimchi, soy sauce, vinegar, soybean meal and so on.

In daily life, people use the appropriate means, such as heating, cooking, storage, baking, fermentation, etc. to enhance or impart food aroma according to the formation of aroma substances in food. In the food processing industry, sometimes it will pass. Add food flavors and fragrances to enhance the characteristic aroma of the food.

Not only do foods have to be fragrant, but we also hope that we can be aroma. The main raw materials for perfumes are flavors and alcohols. In addition, appropriate amounts of pigments, antioxidants, fungicides, glycerin and surfactants are added as needed. Perfume is generally used in an amount of 15% to 25%. Fragrance is a component that imparts aroma to the perfume. The aroma composition is very complex. The fragrance is formulated from a variety of natural or synthetic flavors in a certain proportion. Natural flavors are divided into plant flavors and animal flavors: plant flavors are extracted from the flowers, branches, leaves, roots, skins, stems, seeds or fruits of aromatic plants, and exist in the form of essential oils, tinctures, extracts, Net oil, fragrant resin, oleoresin, balsam, etc. There are many kinds of natural plant spices, such as citrus essential oils, rose essential oils, lavender essential oils, rosemary essential oils, and jasmine essential oils. The types of aroma substances in plants mainly include acids, alcohols, aldehydes, ketones, esters, terpenes, and nitrogen-containing and sulfur-containing compounds.

Animal spices are extracted from animal secretions or excretions. Currently, the four most common animal spices in the world are musk, civet, beaver, and ambergris. Unlike the abundant sources of raw materials in the production of botanical spices, the source of raw materials for animal fragrances is scarce and therefore very expensive. Especially ambergris, which is a secretion in the intestines of sperm whales. After encountering irritating foreign bodies (such as squid and octopus sacrum), the oil and secretions in the whale’s intestines will be wrapped with foreign bodies. The erosion and microbes decompose other organic matter, excrete with the digestive system or vomiting, and then undergo a long oxidative process in seawater, and naturally saponify with the salt and alkali in the ocean to form a dry solid fragrance.

Fermentation gives a special aroma to foods such as kimchi

Essential oils extracted from plants are used to make perfumes

Sperm Whale (Source/Wiki) Ambergris (Image Source / Wiki)

Knowledge link: aroma derived from the ocean
Dragon scent is more expensive than gold. It is often used as a deodorant for high-end perfumes. It makes the fragrance of the perfume more stable and soft, and it has a long-lasting fragrance and is very popular. It is deeply loved by people. The main ingredient of ambergris fragrans is ambroxol, which does not have aroma itself, but after being oxidatively degraded in the air, it produces some scented substances, such as α-myrogen with animal odor, Tobacco-flavored gamma-dihydroionone, seawater-flavored gamma-dragon aldehyde, scented seawater-flavored gamma-ring geranium chloride and legendary “velvet-like long-lasting aroma” The dragon’s ether.