Extending the shelf-life of straw mushroom with high carbon dioxide treatment

Tropical straw mushrooms (Volvariella volvacea) are important ingredients in many Asian dishes, but their rapid browning and weight loss immediately after harvest are the main factors limiting their shelf life to 1-2 days under ambient conditions. In the present study, browning and several physiological changes of straw mushrooms were investigated under various storage temperatures and under high CO2 atmospheric conditions. The browning symptoms initially appeared at the middle of the mushroom cap and at the cut surface 6 h after harvest under ambient conditions (25-34 degrees C, 60-70% relative humidity (RH)) and progressively increased with advancing storage time in parallel with an increase in weight loss. In the browning tissues, the mycelium of the mushroom cap turned brown and collapsed. However, during modified atmosphere (MA) storage with a polyvinyl chloride (PVC) film overwrapping, the browning symptoms of the stored mushrooms still occurred even when the water loss was dramatically reduced. Tyrosine and pyrocatechol were found to be the preferred substrates for the browning reaction. Storage at temperatures below the optimum of 15 degrees C induced more severe browning symptoms due to chilling injury. Malondialdehyde (MDA), a product of lipid oxidation, increased during the first day of storage at ambient temperatures and at 4 degrees C but decreased at 8, 12 and 15 degrees C. Applications of CO2 concentrations of 10 or 20% combined with 15% O-2 during storage effectively decreased browning due to the inhibition of polyphenol oxidase (PPO) activity. Furthermore, exposure to 40% CO2 for 4-6 h prior to MA packing tended to reduce mushroom browning during storage, whereas a 12-h incubation in high CO2 at either 40 or 60% revealed an increase in browning symptoms