Biochemical changes associated with mushroom browning in Agaricus bisporus (Lange) Imbach and Pleurotus florida (Block &Tsao): commercial implications

Biochemical changes associated with mushroom browning in Agaricus bisporus and Pleurotus florida were studied. With increasing storage temperature from 0 to 25 ◦C there was an increase in phenol oxidase activity up to 15 ◦C followed by a decrease at 25 ◦C in both mushrooms. Loss of water content in fresh mushrooms had a direct relationship with phenol oxidase activity, which could be correlated with
the visual degree of mushroom browning. A bisporus displayed higher phenol oxidase activity, about two
to three times that of P florida. The phenol oxidase activity in both mushroom varieties was studied on
a range of phenolic compounds with diverse functional groups. A bisporus exhibited intense reactions to
tyrosine and catechol, while P florida did so to guaiacol and catechol. The two mushrooms differed in
the degree of their oxidation reactions relative to the functional groups. In A bisporus the skin had more
phenolics than the flesh; P florida contained fewer phenolics, while the stalks of both mushrooms had low
phenolics contents. FTIR spectral studies of intact mushrooms during browning showed a characteristic
decrease in phenolic hydroxyls; first-derivative spectra were used to assess relative peak intensities. Of
the chemicals tested for their effect on phenol oxidase activity, 0.1M sodium carbonate favoured the
immediate development of an orange chromogen in P florida, while mild alkaline solutions favoured the
enzyme activity, and acidic solutions at the 0.1M level completely inhibited the browning reaction in both
mushrooms.