EPR investigations of gamma-irradiated ground black pepper

The γ-radiation treatment of ground black pepper samples resulted in the production of three paramagnetic species ( GI– GIII) which arise from a different origin and have different thermal behavior and stability. The axially symmetric spectra can be characterized by the spin Hamiltonian parameters: GI ( g ⊥ = 2.0060 , g ∥ = 2.0032 ; A ⊥ = 0.85 mT , A ∥ = 0.70 mT ) and GII ( g ⊥ = 2.0060 , g ∥ = 2.0050 ; A ⊥ = 0.50 mT , A ∥ = 0.40 mT ) assigned to carbohydrate radical structures. The parameters of EPR signal GIII ( g ⊥ = 2.0029 , g ∥ = 2.0014 ; A ⊥ = 3.00 mT , A ∥ = 1.80 mT ) possessed features characteristic of cellulose radical species. The activation energies, evaluated by Arrhenius analysis, are in order E a( GI)< E a( GIII)< E a( GII). The EPR measurements performed 20 weeks after radiation process confirmed that a temperature increase from 298 to 353 K, caused a significant decrease of integral EPR signal intensity for γ-irradiated samples (∼40%), compared to the reference (non-irradiated) ground black pepper, where a decrease of ∼13% was found. The influence of γ-radiation treatment on the radical-scavenging activities of aqueous and ethanol extracts of black pepper were investigated by both an EPR spin trapping technique and DPPH assay. No changes were detected in either the water or ethanol extracts for a γ-irradiation dose of 10 kGy.