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