Five phenolic carboxylic acids (p-hydroxybenzoic, vanillic, syringic, p-coumaric and ferulic acids) and two cis-acids (p-coumaric and ferulic acids) were identified in water-oat by GC-MS, while four acids (p-hydroxybenzoic, vanillic, syringic and p-coumaric acids) were found in the exudate of the plant. The amounts of the acids determined by GC varied from 100 μg/g for vanillic acid to 580 μg/g for p-coumaric acid in the plant, and from 53 μg/l for p-coumaric acid to 140μg/l for syringic acid in the exudate. The comparison of the composition of the acids in the plant with that in the exudate showed that p-hydroxybenzoic, vanillic and syringic acids were more easily moved from the plant into water than p-coumaric and ferulic acids. It was suggested that the latter has an ethylenic double bond attached to the side chain.
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