Browning Metabolism Research During The Storage Of Agaricus Bisporus

Postharvest browning of Agaricu bisporus is a severe problem that is common andeconomically detrimental. Post-harvest, Agaricu bisporus immediately starts to loss water andbegins to brown in color. With3days room-temperature storage, Agaricu bisporus would be outof product acceptability. Three aspects were studied in this passage:1. key factors to thebrowning of Agaricus bisporus during storage;2. how storage temperature affected the activeoxygen metabolism and also phenol metabolism including relationships between them and/orAgaricus bisporus browning;3. the separation of phenol substrates via HPLC and analysisthrough LC-ESI-MS. Detailed results are as follow:1.Key factors to the browning of Agaricus bisporus during storageAgaricus bisporus was stored for9days at (5±0.5)℃and (50±5)%RH and conducted in thestorage of (5±0.5)℃and (90±5)%RH as control. Water loss, whiteness, cell membranepermeability, production of O₂-, and malonaldehyde (MDA) were monitored during storage. Theresults revealed that certain water loss (≥8%) caused the reduction of whiteness, increase of O₂-production, MDA content, and also cell membrane permeability. Water loss precedes browningoccurrence and over time, water loss is related to browning. These results indicated that waterstress influence browning of Agaricus bisporus directly by affecting cell membrane structure butactive oxygen metabolism. The accumulation of O₂-with increased water loss only promoted thedamage of cell membrane structure. Product acceptability is rush down once the water loss up to5%, however. Consequently, though certain water loss caused postharvest browning, water lossstill can't be the key fact affecting the postharvest browning of Agaricus bisporus during storage.Studies on storage at different temperature revealed that low temperature could effectively helpthe delay of browning and the extent of shelf life. The lowest browning index and the longeststorage time were found at (1±0.5)℃,(90±5)%RH. Consequently, temperature is the key to thestorage of Agaricus bisporus.2. How storage temperature affected the active oxygen metabolism and also phenolmetabolism including relationships between them and/or Agaricus bisporus browningAgaricus bisporus was stored at (1±0.5)℃,(4±0.5)℃,(8±0.5)℃and (90±5)%RHseparately. Browning index, and other parameters related with active oxygen metabolism orphenol metabolism were monitored. The results indicated that storage temperature producedsignificant effect. Lower the temperature was, less the accumulation of O₂-, H2O₂and higher theactivities of SOD, CAT were. Low temperature was able to delay the occurrence of total phenolcontent, PPO and POD peaks. Principal Component Analysis explained86.45%of the data, and with Partial Least Squares Regression, Path Analysis together, demonstrated the cell membranepermeability, PPO, browning index as key fators; and H2O₂level as the most importantparameters for cell membrane permeability; PPO, cell membrane permeability and POD, as theimportant ones for browning index.3. the sepration of phenol substrates via HPLC and analysis of LC-ESI-MSPhenol substrates during storage and pre-or after-reacted with PPO/POD ones wereseparated by HPLC and were analysed by LC-ESI-MS. Results suggested that phenol substrateschanged after the occurrence of PAL peak, especially shown as its content increcing. PPO andPOD of Agaricu bisporus had different affinity with phenol substrates. There might be asequential reaction. POD firstly reacted with certain phenol substrate, and then the product,which was similar with catechol, oxidized by PPO and finally changed into black pigment. Themajor phenol substrates might be Tyrosine, Dopa and Caffeic acid.