Tannins in food

The term “tannin” covers a wide range of naturally occurring compounds of varying structure scattered widely throughout the vegetable kingdom.

Tannins (commonly referred to as tannic acid) are water-soluble polyphenols that are present in many plant foods. They have been reported to be responsible for decreases in feed intake, growth rate, feed efficiency, net metabolizable energy, and protein digestibility in experimental animals.

Tannins are astringent, bitter plant polyphenols that either bind and precipitate or shrink proteins. They are composed of a very diverse group of oligomers and polymers.

They can have a large influence on the nutritive value of many foods eaten by humans and feedstuff eaten by animals. Tannins are common in fruits (grapes, persimmon, blueberry, etc.), in tea, in chocolate, in legume forages (trefoil, etc.), in legume trees (Acacia spp., Sesbania spp., etc.), in grasses (sorghum, corn, etc.).

Because tannins bind with other proteins, including those in human saliva, they create a characteristic astringent, mouth-coating sensation in the mouth.

Their primary role in nature is to make unripe fruits and seeds unpalatable, thus dissuading animals from eating them.

Tannins are a class of compounds in tea, especially black tea, which tend to have a bitter flavor and astringent properties. Tea high in tannins can be described as tannic.
Tannins in food

Naringin in fruit

Flavonoids are naturally occurring phenolic compounds with a diverse range of bioactivities. Approximately 4000 flavonoids have so far been discovered, mainly from fruits, vegetables, and herbs.

Flavonoids in citrus fruit include flavanones (naringin), flavones (nobiletin), and flavonols (quercetin). Naringin, a flavanone neohesperidoside, and neohesperidin are very bitter, whereas hesperidin is tasteless.

Naringin (with the molecular formula C27H32O14 and a molecular weight of 580.4 g/mol) is responsible for the fruit's bitter taste in citrus fruit especially in grapefruit. It possesses the distinct bitter taste of grapefruit juice. Two rhamnose units are attached to its aglycon portion, naringenin, at the 7-carbon position.

Naringin concentrations are highest in young leaves and in the pulp of immature fruit. Naringin was found to possess strong antioxidant and anti-inflammatory activities both in vitro and in vivo.
Naringin in fruit