Detection of Free Radicals in Electron Beam-Irradiated Mucuna pruriens (L. DC.) Seeds by Electron Spin Resonance

Abstract

Electron spin resonance (ESR) spectroscopy was employed to detect free radicals in raw Mucuna pruriens (velvet bean) seeds after electron beam irradiation (Microtron source: 0, 2.5, 5, 7.5, 10, 15 and 30 kGy) and conventional processing (roasting, powdering and cooking). The ESR signal of irradiated seeds (g=2.0055±0.0001) was more prominent in the seed coat than cotyledon. Seed coat of irradiated samples showed dose-dependent linear increase of this signal (g = 2.0055) accompanied by a weak triplet (satellite peak; aH = 3 mT) produced exclusively by radiolysis and could be used as an indication of successful irradiation. Irradiated cotyledon portion devoid of satellite peak (triplet) showed a linear increase in signal intensity up to 10 kGy with a sharp decline at higher doses (15 and 30kGy). Stability of radiation-induced ESR signals after 6 months of storage (25 ± 1°C) revealed the presence of a weak triplet with a substantial loss of signal intensity. Thermal effects such as roasting and powdering of seeds increased the signal intensity (g = 2.0055) similar to or in greater proportion than irradiation. Phenolics in seeds, which contribute significantly to detect free radicals in vegetative parts of a plant showed a waning trend in seed coat, while it was vice versa in cotyledon. Textural studies revealed significant loss in firmness after irradiation (p<0.05), which might favour in minimising the cooking time. Results of the present study might help to divulge the beneficial effects of application of electron beam irradiation technology as a better alternative to fumigants in seed preservation for safety and quarantine purposes.