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Recommendations for Maintaining Postharvest Quality

Trevor V. Suslow and Marita Cantwell Department of Vegetable Crops, University of California, Davis,CA 95616

Maturity Indices
Agaricus bisporus mushrooms (Button Mushrooms) are harvested by maturity and not by size. Maturity is reached when the caps are well- rounded and the partial veil is completely intact. The stipe (stalk) should have a small length to thickness ratio. Stipe length should be sufficient to permit some trimming without cutting flush to the veil.

Quality Indices
Good quality, fresh ‘Agaricus’ mushrooms should be white to dark brown. White forms are most prevalent. Uniform, well rounded cap with a smooth glossy surface and fully intact veil are indicators of best quality. Stipes are straight and glossy in appearance with an even cut edge. Cleanliness (minimal growth medium residue) and absence of browning or other discoloration are additional quality factors. Visible, open gills and absence of a stipe are negative factors.

U.S. grades are No. 1 and No. 2. Sizes range from Small {Button} ( 1.9 – 3.2cm / .75 – 1.25 in. ), Medium ( 3.2 – 4.5cm / 1/25 – 1.75 in.), to Large ( 4.5 cm / 1.75 in. and larger) measured as cap diameter. Grades discriminate for maturity, shape uniformity, cleanliness and trim quality.

Optimum Temperature
0° – 1.5°C ( 32° – 35°F ) Storage life is typically 5-7 days at 1.5°C(35°F) and 2 days at 4.5°C (40°F).

Optimum Relative Humidity
95-98 %; High relative humidity is essential to prevent desiccation and loss of glossiness. Drying is correlated with blackening of the stipe and gills and curling of the cap. Commonly mushrooms are packed and shipped in cartons with a perforated overwrap to maintain high humidity.

Rates of Respiration

°C     °F
mg CO2/kg·hr
0     32 28-44
5     41 71
10    50 100
15     59 NA
20   68 264-316
25    77 NA

To calculate heat production multiply ml CO2/kg&3183;hr by 220 to get Btu/ton/day or by 61.2 to get kcal/metric ton/day. NA= not applicable

Rates of Ethylene Production
>0.1µl / kg·hr at 20°C (68°F)

Responses to Ethylene
Agaricus mushrooms are not significantly impacted by exogenous ethylene.

Responses to Controlled Atmospheres(CA)
Extended storage ( ~12-15 days ) in 3% O2 and 10% CO2 at 0°C has been Controlled demonstrated. Elevated CO2 at 10-15 % ( typically 10% ) in air is beneficial in Atmosphere (CA) preventing decay and reducing the rate of blackening of the stipe and gills. The beneficial effect is most pronounced if temperatures cannot be maintained below 5°C ( 41°F ). Short exposure to higher CO2 concentrations (20 %) is safe and beneficial only if temperatures can be maintained at 0° – 1°C (32° – 34°F).

Improper control of controlled atmospheres or improper packaging can rapidly lead to depletion of oxygen resulting in conditions favorable for Clostridium botulinum. For this reason, primarily, the use of CA and MA is not common.

Physiological & Physical Disorders
Mushrooms will continue to develop after harvest which is why low & Physical temperature postharvest management is critical. Common disorders include Disorders upward bending of caps and opening of the veil.

Mushrooms are easily bruised by rough handling and develop patches of browning discoloration.

Freezing injury ( water-soaked appearance leading to extreme softening ) will likely result at temperatures of -0.6°C ( 30.9°F) or lower.

Signs of CO2 injury are blackening and pitting.

Pathological Disorders
Disease is generally not an important source of postharvest loss in comparison with physiological senescence and improper handling or bruising. Diseases, such as Bacterial Blotch, and spoilage due to other Pseudomonas spp. are generally eliminated during the harvest or sorting phases although development of patches of decay can occur with elevated temperature or extended storage.

Special Considerations
Rapid forced-air cooling soon after harvest is strongly recommended. Center-loading during shipment promotes good cooling-air circulation necessary for this commodity. Good arrival following surface transportation is enhanced when trailers are equipped with ‘air-shocks’ suspension. Agaricus mushrooms are reported to acquire strong odors, such as onion, in mixed loads or short term storage.

Postharvest Technology Research and Information Center
Department of Pomology
University of California
One Shields Ave., Davis, CA 95616-8683

Send comments and questions to Postharvest Technology Research and Information Center
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Produce/ProduceFacts/Veg/mushroom.html updated July 10, 2000

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