Analysis of Agaricus bisporus tyrosinase activation and phenolics utilization during Pseudomonas tolaasii or tolaasin-induced discolouration

Discolouration due to senescence differs from blotch-related discolouration , which might indicate differential mechanisms being operational. In sample s infected with bacteria or with a partially purified toxin extract, a high er degradation of total tyrosinase than in senescening mushrooms was found. Simultaneously, the active tyrosinase was increasing resulting in an incre ase in percentage of active tyrosinase. Phenolic substrates of the active t yrosinase were being oxidized, proportionally to the damage detectable on t he mushroom cap, gamma-Glutaminyl-3,4-dihydroxybenzene was degraded first, followed by gamma-glutaminyl-4-hydroxybenzene and later tyrosine. The amoun t of melanin that was synthesized was larger than the sum of oxidation of t he phenols measured. Principal Component Analysis explained 84% of the vari ance in symptoms, and it demonstrated the phenol oxidation and active tyros inase level as the most important parameters for the browning induced by ba cteria or a tolaasin preparation treatment.