Using onion extract as an inhibitor of enzymatic browning in A. bisporus mushrooms during 8-month frozen storage had promising results: the effects were stronger than the organic acid solution but weaker than the sodium metabisulphite solution. The colour of frozen A. bisporus varied according to the ratio of diphenolase activity to monophenolase activity:the lower the value of this coefficient, the lighter the colour.The maintenance of light colour depends on reducing diphenolase activity and balancing diphenolase and monophenolase activity. Onion extract had a beneficial effect on the flavour and aroma of mushrooms.