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Abstract: To improve our knowledge of the most relevant biochemical factors involved in the browning process of Agaricus bisporus, we compared tyrosmase activities and phenols (nature and content) in two strains B62 and S609 having high and low susceptibilities to browning, respectively The phenol content in the skin (tyrosine, GHB and GDHB) was nearly sevenfold higher in the B62 than m the S609 strain With commercial enzyme and saturating substrate concentrations, the apparent Vm and A^M values were first determined for DOPA, tyrosine and GHB, respectively Using mushroom extracts, we also followed the enzymatic oxidation of a mixture of three phenols (tyrosine, GHB, GDHB) present at the same concentrations as in the cap skin from A. bisporus B62 Using this m vitro model, the rates of substrate consumption paralleled Vm values for these extracts diphenol > tyrosine > GHB We did not observe significant differences in the enzyme activities between the two strains, in each case, the active fraction of tyrosinase appeared very important when compared to phenol levels We thus came to the same conclusion as Burton (Enzyme Microb Technol 1993 15 436 741) the phenol content appeared as the limiting factor of browning process and could largely explain the different susceptibilities of the strains towards discoloration
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