Phenolic acids of walnut (Juglans regia L.)

GRZEGORZ CHRZANOWSKI, BOGUMIŁ LESZCZYŃSKI, PAWEŁ CZERNIEWICZ, HUBERT SYTYKIEWICZ, HENRYK MATOK, ROBERT KRZYŻANOWSKI

Abstract

The chromatographic separations showed the presence of eleven free phenolic acids (trans-cinnamic, o-coumaric, p-coumaric, chlorogenic, ferulic, gallic, caffeic, p-hydroxybenzoic, syringic, tannic and vanillic) in the walnut tissues. The p-hydroxybenzoic acid was a predominant compound in the green husks (618.8 µg·g-1), though, high content of it was found in leaves obtained in July (478.3 µg·g-1). The content of chlorogenic acid in green husks of walnut (306.7 µg·g-1) was twice higher than that in the leaves obtained in July. Similar level of coumaric acids was determined in the leaves and green husks (o-coumaric: 42.4–48.2 µg·g-1; p-coumaric: 78.6–94.3 µg·g-1), though, o-coumaric acid was not found in May-leaves. Moreover, leaves of walnut possessed high content of caffeic acid (leaves obtained in May – 456.9; leaves obtained in July – 262.1 µg·g-1) and ferulic acid (leaves obtained in May – 93.5; leaves obtained in July – 292.5 µg·g-1). The predominant compound of the male inflorescences was vanillic acid (359.5 µg·g-1). The green husks of walnut were rich in polyphenolic acids, syringic (427.0 µg·g-1) and tannic (237.4 µg·g-1). However, the content of tannic acid was higher in the leaves - especially in leaves collected in May (350.7 µg·g-1). In tested tissues of walnut, gallic acid was found in the lowest concentration (male inflorescences – 32.7 µg·g-1and leaves obtained in July – 12.7 µg·g-1). In general, there was a great variation in a level of the phenolic acids between the studied organs of the walnut; nevertheless, walnut tissues are precious source of phenolic acids.
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