The role of simple carbohydrates in the suppression of hydroxyl free radicals in γ-irradiated papaya juice

Abstract

Hydroxyl free radical (HO ·), reactions with a series of trapping agents, such as 2-deoxyribose, 2-hydroxybenzoic acid or dimethylpyrroline N-oxide, are effectively blocked when dilute solutions of papaya jice are added to irradiation mixtures prior to exposure to 60Co γ-rays. Our studies to determine the agents present in papaya juice responsible for the HO · quenching activity suggest that glucose, fructose and sucrose, present in papaya juice in total concentrations of ∼0·5–0·7 molar, block HO · reactions and produce malonaldehyde and other sugar derivatives when the juice is exposed to γ-rays. Papaya contains a sequestered invertase which is released when the fruit is crushed during juice extraction. Heat treatment of the fruit before juice preparation inactivates this enzyme, and the juice of this fruit contains lower total amounts of the simple sugars and is a proportionally poorer quenching agent than the unheated juice. Synthetic mixtures of the simple sugars at concentrations equal to those in papaya juice mimic the inhibition of HO · reactions and the production of malonaldehyde by papaya juice.