Effect of gamma-irradiation on phenylalanine ammonia-lyase activity, totalphenolic 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 effec t of the gamma -irradiation on some biochemical parameters. Irradiation at doses of 1.5 kGy and 2.5 kGy reduced significantly (p less than or equal to 0.05) the rate of respiration of the mushrooms, compared to that of sample s irradiated at 0.5 kGy and nonirradiated control samples (C). Ionizing tre atments increased significantly (p less than or equal to 0.05) the phenylal anine ammonia-lyase (PAL) activity and total phenols concentration between days I and 4. From days 3-4, to the end of the storage period (day 12), bot h PAL activity and total phenols in the irradiated samples (I) collapsed to lower values. In contrast, the activity of polyphenol oxidase (PPO) increa sed until days 7, 9, and 12 for samples treated at 0.5, 1, and 2 kGy, respe ctively. Color measurements showed a loss of whiteness (L* value) during st orage. After day 4, however, the effectiveness ef gamma -irradiation became apparent, and highest L* values were obtained for I only.