Effects of high CO2 treatments on alleviation of straw mushroom browning: The controlled atmospheres with high CO2 concentrations of 10% or 20% combined with 15% O2 effectively retarded the browning of the straw mushrooms during storage at 15ºC with 90-95% RH (Fig. 5A). This effect was attributed to the inhibition of PPO activity, particularly after 2-4 days of storage (Fig. 5B). High CO2 treatments have been reported to control browning generation by inhibiting PPOs in fresh produce 24-26. Furthermore, tyrosine was the preferred precursor for the browning reactions (Fig. 6A) compared with phenylalanine (Fig. 6B), cinnamic acid (Fig. 6C) and the control in distilled water (Fig. 6E), which was similar to the browning reported in Agaricus bisporus6- 8. Incubation with phenylalanine, a product of the shikimic pathway (the same as tyrosine), did not show much browning, suggesting that melanin polymerisation from L-dopa oxidation 27, 28 from tyrosine may be the main pathway of browning in straw mushrooms. However, the browning evidence in the pyrocatechol