Effect of gamma-irradiation on phenylalanine ammonia-lyase activity, total phenolic content, and respiration of mushrooms (Agaricus bisporus).

Ionizing treatments were applied at 0.5 kGy, 1.5 kGy, and 2.5 kGy to edible mature mushrooms (Agaricus bisporus, albidus) in order to assess the effect of the gamma-irradiation on some biochemical parameters. Irradiation at doses of 1.5 kGy and 2.5 kGy reduced significantly (p < or = 0.05) the rate of respiration of the mushrooms, compared to that of samples irradiated at 0.5 kGy and nonirradiated control samples (C). Ionizing treatments increased significantly (p < or = 0.05) the phenylalanine ammonia-lyase (PAL) activity and total phenols concentration between days 1 and 4. From days 3-4, to the end of the storage period (day 12), both PAL activity and total phenols in the irradiated samples (I) collapsed to lower values. In contrast, the activity of polyphenol oxidase (PPO) increased until days 7, 9, and 12 for samples treated at 0.5, 1, and 2 kGy, respectively. Color measurements showed a loss of whiteness (L value) during storage. After day 4, however, the effectiveness of gamma-irradiation became apparent, and highest L values were obtained for I only.