On the phenolic acids of vegetables. IV. Hydroxycinnamic acids and hydroxybenzoic acids of vegetables and potatoes
Schmidtlein, H.; Herrmann, K.
Zeitschrift für Lebensmittel-Untersuchung und -Forschung 159(5): 255-263
Lettuce, endive and chicory exclusively, cornsalad and sweet fennel almost exclusively contain caffeic acid derivatives beside traces of ferulic acid. Parsley exclusively and spinach almost exclusively show p-coumaric acid derivatives. Compared to root, fruit and seed vegetables the contents of phenolic acids in green leaves are considerably high. Rhubarb is the only vegetable, which contains gallic acid (chief phenolic acid) beside hydroxycinnamic, protocatechuic and vanillic acid derivatives. Furthermore hydroxybenzoic acid derivatives (salicylic, gentisic and vanillic acid) occur in cornsalad, sweet fennel, parsley and spinach in small concentrations; cornsalad shows p-hydroxybenzoic acid (ca. 20 mg/kg). Onions (Allium cepa) contain almost only protocatechuic acid beside small amounts of p-hydroxybenzoic and vanillic acid. In the outer dry coloured skins protocatechuic acid reaches concentrations up to 2% of plant material; the internal pulpy tissues show lower concentrations (ca. 20 mg/kg). On the contrary to the bulbs the green leaves of onions like chive and leek contain almost exclusively compounds of ferulic and p-coumaric acid. Garlic even shows a different phenolic acid pattern of skins and internal tissues. The caffeic acid derivatives of potatoes are mainly localized to a 1--2 mm thick outer layer. The different localization of phenolic acids in the different parts of vegetable plants is discussed.