Phenolic compounds in vegetables

Among food products that are rich sources of phenolic compounds, fruit and vegetables. Polyphenols are subdivided into several major subclasses: phenolic acids, stilbenes, tannins, diferuloylmethanes and flavonoids.

Many previous studies have shown that vegetables are composed of many non-nutritive substances including polyphenol compounds which are beneficial to humans.

Cherry tomatoes contained 17−203 μg of quercetin (a type of flavonoid) g-1 fresh weight compared to 2.2−11 μg g-1 detected in normal-sized Scottish, Spanish, and Dutch beef tomatoes. The quercetin levels in onions ranged from 185 to 634 μg of quercetin g-1 fresh weight. “Round” lettuce contained 11 μg of quercetin g-1 fresh weight compared to 911 μg g-1 in the outer leaves and 450 mg g-1 in the inner leaves of “Lollo Rosso” lettuce (J. Agric. Food Chem., 1997, 45 (3), pp 590–595).

In general, the flavonoids group dominate among vegetable polyphenols and it was found that flavonoids share in total content of polyphenols in vegetables was in range of 51-79%.

Japanese and Chinese folk medicines frequently used plants rich in vegetable tannins (or polyphenols) which are regarded as the active principles of herbal remedies.

They have been employed in the treatment of inflammation, liver injury, problems of the kidney, arteriosclerosis, blood pressure, hypertension, nervous and hormonal problems, stomach disorders, ulcers and to inhibit mucous secretions and so forth.
Phenolic compounds in vegetables