Radiation Chemistry of Foods

In food irradiation, water-soluble food constituents undergo the attack of ${\text{e}}_{\text{aq}}^{-}$ and OH at the neutral region. Reaction rate constants of some food constituents with ${\text{e}}_{\text{aq}}^{-}$ and OH were measured by competition methods using nitrous oxide and ³H-formate as competitors, respectively. High selectivity was observed among the reactions with ${\text{e}}_{\text{aq}}^{-}$ and the ${\text{e}}_{\text{aq}}^{-}$-reaction rate constants are 10¹⁰ M⁻¹ sec⁻¹ (cysteine), 10⁹ M⁻¹ sec⁻¹ (methionine, ascorbic acid, and histidine), and much smaller (sugars, and the other types of amino acids). The OH-reaction rate constants range from 10⁹ M⁻¹ sec⁻¹ (cysteine, histidine, methionine, aromatic amino acids, and ascorbic acid) to 10⁸ M⁻¹ sec⁻¹ (sugars and the other amino acids), indicating that the reactions with OH are less selective. Selective destructions of cysteine and ascorbic acid in food irradiation may be partly ascribed to their selective reactivities with some less reactive species which are produced by reactions of ${\text{e}}_{\text{aq}}^{-}$ or OH with oxygen or the other constituents as well as their higher reactivity with ${\text{e}}_{\text{aq}}^{-}$.