Lignin and organic free radicals in maize (Zea mays L.) seeds in response to aflatoxin B1 contamination: an optical and EPR spectroscopic study

Abstract

Aflatoxin B1 (AFB1), is a naturally hazardous environmental contaminant, contained mainly in various cereal seeds. The maize (Zea mays L.) seeds containing various levels of the AFB1 was investigated using optical and electron paramagnetic resonance spectroscopies. The changes of lignin content and organic free radicals as indicators of the seeds' defense response to the AFB1-stressor were estimated, in the seeds' inner and outer fractions. The lignin content was determined using the Acetyl Bromide method. No correlation was found between the lignin content and the AFB1 concentration in the inner fraction (R of 0.030, p = 0.943), while a significant positive linear correlation (R of 0.9923, p= 0.00005) between the lignin content and the AFB1 concentration in the outer fraction was obtained. Employing electron paramagnetic resonance (EPR) spectroscopy, the different response of the fractions was observed, regarding the content of free radicals with increasing AFB1 concentrations. In addition, front-face fluorescence spectroscopy in combination with the deconvolution showed a positive linear correlation between the ratio of the green and blue spectral emission components (C4/C2) area and the AFB1 concentration in the outer fraction. Thus lignin content and the (C4/C2) area ratio may be reliable indicators for the screening of lignin changes related to the level of AFB1 in the seeds.