Behavior of phenolic substances in the decaying process of plants

Abstract

p-Coumaric, ferulic, vanillic, and p-hydroxybenzoic acids, the main phenolics in rice straw and its decayed products, were incubated at 50°C at concentrations of 30 ppm in dilute water-extract solutions of decayed straw and soil. The dynamics of the individual phenolics and their degradation producta were studied, and the fate and behavior of each phenolic acid in the decaying process of plants were also discussed. The following results were obtained: 1) These phenolic acids were degraded rapidly in a short period. Their half lives were less than 10 days under the experimental conditions used here. 2) The degradation rates of p-hydroxybenzoic and p-coumaric acids were approximately the same in both extract solutions of decayed straw and soil, but vanillic and ferulic acids, which contain methoxy groupings, disappeared much more rapidly in the soli extract solution than in the decayed straw extract solution. 3) When these 4 phenolic acids were added all together into the decayed straw extract solution, they were degraded more slowly than in solutions of individual acids, especially p-coumarlc and ferulic acids which are cinnamlc acid derivatives. 4) A major degradation product of p-coumaric acid, after treatment with diazo-methane, was isolated by preparative gas chromatography and determined as p-methoxycinnamic acid methylester by IR spectroscopy and mass spectrometry. The product itself was identified as p-methoxycinnamic acid by co-chromatography with the authentic sample. A major degradation product ot ferulic acid was Identified as 3,4-dimethoxycinnamic acid in the same way. 5) p-coumaric and ferullc acids were transformed rapidly to large amounts of p-methoxycinnamic and 3,4-dimethoxycinnamic acid, respectively, by probably reveraible reactions. These in turn were gradually transformed into small amounts of p-hydroxybenzoic acid and vanillic acid, respectively. p-hydroxybenzoic acid was rapidly transformed to protocatechuic acid. Vanillic acid was rapidly degraded, but no product was detected by gas chromatography. 6) The possible degradation pathway of these phenolic acids in the decaying process of planta is presented.