Naringenin is a flavanone from the flavonoid group of polyphenols. It is commonly found in citrus fruits, especially as the predominant flavonone in grapefruit.
Structure
Naringenin has the skeleton structure of a flavanone with three hydroxy groups at the 4′, 5, and 7 carbons. Racemization of (S)-(−)-naringenin has been shown to occur fairly quickly.
Sources and bioavailability
Naringenin and its glycoside has been found in a variety of herbs and fruits, including grapefruit, oranges, and lemons, sour cherries, tomatoes, cocoa, Greek oregano, water mint, as well as in beans. Ratios of naringenin to naringin vary among sources,
Grapefruit juice can provide much higher plasma concentrations of naringenin than orange juice.
Naringenin can be absorbed from cooked tomato paste. There are 3.8 mg of naringenin in 150 grams of tomato paste.
Biosynthesis and metabolism
Flavonoid biosynthesis in plants uses a phenylpropanoid metabolic pathway in which the amino acid phenylalanine is converted to 4-coumaroyl-CoA. This is combined with malonyl-CoA to yield a group of compounds called chalcones, which contain two phenyl rings. In the case of naringenin, the precursor is naringenin chalcone produced by the enzyme chalcone synthase. This can cyclise spontaneously but would provide racemic material. The enzyme chalcone isomerase constrains the reaction to give only the (S) isomer of the flavanone.
The enzyme naringenin 8-dimethylallyltransferase uses dimethylallyl diphosphate and (2S)-naringenin to produce diphosphate and 8-prenylnaringenin. Cunninghamella elegans, a fungal model organism of the mammalian metabolism, can be used to study the naringenin sulfation.
In plants, the biosynthetic pathway to anthocyanins continues when the enzyme flavanone 3-dioxygenase inserts a hydroxyl group into the dihydropyran ring:
This alpha-ketoglutarate-dependent hydroxylase requires α-ketoglutaric acid, which is converted to succinic acid as a by-product. Aromadendrin is a precursor to many other derivatives.
In some citrus fruits, naringenin is converted to prunin, the precursor to naringin, a compound which is responsible for the bitter taste of grapefruit.
Enzymes with this activity include flavanone 7-O-beta-glucosyltransferase, which uses UDP-glucose to transfer the sugar component.
Metabolic fate after dietary intake
Naringenin can be produced from dietary naringin by the hydrolytic action of the liver enzyme naringinase. The biological activities of naringenin metabolites are unknown, and likely to be different in structure and function from those of the parent compound.