Is this delicious? Could our sense of smell be deceiving us?

"This egg waffle is really delicious!" "Is it? I think the waffle is tastier." Whether food is delicious has always been a subjective feeling; some people think this is tasty, while others think it is not. However, there is one factor that can indeed affect the deliciousness of food, which is the smell of the food before it enters your mouth.  

Fragrance and stench may seem subjective, but they can actually be measured scientifically, known as the indol level of the substrate.

(Indole) is an organic compound with a distinctive aromatic smell. It is a nitrogen-containing cyclic compound commonly found in natural substances, such as certain plant oils, metabolic products in animals, and coal tar. Indole is also used in the preparation of dyes, perfumes, and pharmaceuticals. In biochemistry, indole is an important structural unit, exhibiting various biological activities within living organisms.

Indole affects our sense of smell because it has a strong aromatic odor. When we smell indole, it interacts with our olfactory receptors, triggering specific chemical reactions, which lead to our perception of this particular smell. Various odor molecules bind to specific receptors in our olfactory system, triggering nerve signals that are then interpreted by the brain as specific odor perceptions. Therefore, the molecular structure and properties of indole enable it to produce the aromatic odor we perceive.

For example, stinky tofu is usually made by fermenting tofu, and indole is a common organic compound that may be present during the fermentation process. Indole is a nitrogen-containing cyclic compound with a distinctive smell. In some fermented foods, indole compounds may be one of the reasons for the formation of their unique odor.

Indole is a solid at room temperature. Indole is widely distributed in the natural environment, especially in human and livestock feces, and has a strong fecal odor; however, indole at very low concentrations has a floral scent and is a component of many floral aromas such as orange blossom. Indole is also found in coal tar. Indole can also be used to make perfumes, so it cannot be strictly defined as pleasant or foul smelling. 

Many organic compounds contain the indole structure, including tryptophan as well as tryptophan-containing proteins, alkaloids, and pigments. Cruciferous vegetables such as cauliflower, cabbage, and bok choy are rich in indole, mainly in the form of glucosinolates. During cooking and digestion, these glucosinolates may be converted into indole, which can have anti-inflammatory, antibacterial, and antioxidant effects. The indole in these foods helps maintain human health. 

Note: Indole itself does not have direct anti-inflammatory, antibacterial, or antioxidant effects, but after being metabolized in the human body, some of its metabolites may have these effects.