| Abstract
| - To enhance the shelf life of edible mature mushrooms, Agaricus bisporus, 2 kGy ionizing treatmentswere applied at two different dose rates: 4.5 kGy/h (I-) and 32 kGy/h (I+). Both I+ and I- showeda 2 and 4 day shelf-life enhancement compared to the control (C). Before day 9, no significantdifference (p> 0.05) in L* value was detected in irradiated mushrooms. However, after day 9, thehighest observed L* value (whiteness) was obtained for the mushrooms irradiated in I-. Analysesof phenolic compounds revealed that mushrooms in I- contained more phenols than I+ and C, thelatter containing the lower level of phenols. The fluctuation of the precursors of glutaminyl-4-hydroxyaniline (GHB) was less in I- than in I+. The polyphenol oxidase (PPO) activities of irradiatedmushrooms, analyzed via catechol oxidase, dopa oxidase, and tyrosine hydroxylase substrates, werefound to be significantly lowered (p = 0.05) compared to C, with a further decrease in I+. Analysesof the enzymes indicated that PPO activity was lower in I+, contrasting with its lower phenolsconcentration. The observation of mushrooms' cellular membranes, by electronic microscopy, revealeda better preserved integrity in I- than in I+. It is thus assumed that the browning effect observedin I+ was caused by both the decompartmentation of vacuolar phenol and the entry of molecularoxygen into the cell cytoplasm. The synergetic effect of the residual active PPO and the molecularoxygen, in contact with the phenols, allowed an increased oxidation rate and, therefore, a morepronounced browning I+ than in I-. Keywords: Agaricus bisporus; browning; polyphenol oxidase (PPO); phenols; γ irradiation.
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