Storage of mushrooms in pre‐packs: The effect of changes in carbon dioxide and oxygen on quality

Mushrooms (Agaricus bisporus) were picked at the “button” stage (velum differentiated but unbroken) and stored for 3 to 5 days at 2 or 18 °C in styrene punnets (pre-packs) overwrapped with one of a range of plastic films. Concentrations of carbon dioxide and oxygen were measured inside the pre-packs at intervals. When the packs were opened, internal and external browning, loss of weight and diameter of the mushrooms were measured and subjective assessments of quality were made. These parameters were compared with those of mushrooms stored in unwrapped punnets. As a result of the mushroom respiration, the internal atmosphere of the prepack was rapidly modified until, after about 24 h, a rough equilibrium concentration of CO2 and O2 was established in the range 4 to 10% CO2 and 11 to 17% O2 at 2 °C or 8 to 15% CO2 and 1 to 2% O2 at 18 °C; the mean concentration was dependent on the type of film. An equation, applicable to five out of six films that were tested, is proposed to describe the relationship between the equilibrium CO2 concentrations at 18 °C and the permeability data of the film. At 18 °C, the gas changes inside the pre-packs prevented opening of the pileus and, in combination with prevention of water loss by the film, slowed down deterioration of the mushrooms. However, concentrations of CO2 much above or below 10 to 12% were associated with increased internal browning. At 2 °C overwrapping generally caused slight external browning of the pileus. The relevance of the results are discussed in relation to the commercial marketing of pre-packed mushrooms.