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article imageWhy do mushrooms turn brown?

By Tim Sandle     Sep 12, 2014 in Odd News
Vienna - Mushrooms are a tasty addition to many meals. However, when they go brown, they become inedible. Why does this happen and can the process be slowed down? Food technologists have been looking into this subject.
A science team have examined the mechanisms behind the 'browning reaction' during the spoilage of mushrooms. The scientists demonstrate that is due to an enzyme, and this enzyme is already formed prior to the browning reaction beginning; it smiply waits for a certain time point and biochemical trigger.
Edible mushrooms include many fungal species that are either harvested wild or cultivated. Easily cultivatable and common wild mushrooms are often available in markets and are a popular foodstuff. Some are more difficult to obtain (such as the prized truffle and matsutake). All types of mushroom have a biological “use by date” indicated by the mushroom turning brown.
The research established that six different enzymes (of the type tyrosinases) exist within the mushroom. Two of these (termed PPO3 and PPO4) occur in larger quantities. When these enzymes react this triggers a specific chemical cleavage. At this cleavage site, the protein segment covering part of the enzyme active site is removed and certain substrates (tyrosine and other monophenols) are accessed and take part in key chemical reactions, which leads to food spoilage. This enzyme is found in many animals, as well as fungi. The enzyme is part of the protective pathway against ultra-violet radiation.
Now that the research has pinpointed a copper-containing enzyme, it could be possible to slowdown or inhibit the enzyme, thereby preserving mushrooms for longer. Arguably, the research has wider implications for food spoilage in general. Mushrooms were selected for the study as an ideal model organism for the examining the pathway involved in food spoilage.
The research was led by Annette Rompel from the Institute for Biophysical Chemistry, University of Vienna. The findings have been published in the journal Phytochemistry. The paper is titled “High level protein-purification allows the unambiguous polypeptide determination of latent isoform PPO4 of mushroom tyrosinase”.
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