Explain how blanching affects the enzyme, polyphenol oxidase, to stop the browning process.While watching a cooking show, you learn that the browning of fruits such as apples is a chemical...

Explain how blanching affects the enzyme, polyphenol oxidase, to stop the browning process.

While watching a cooking show, you learn that the browning of fruits such as apples is a chemical reaction. It is catalyzed by an enzyme called polyphenol oxidase. To prevent browning, the cooking show suggests that you blanch the fruit by placing it on boiling water or steam for a short time.

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Explain how blanching affects the enzyme, polyphenol oxidase, to stop the browning process.

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pacorz | High School Teacher | (Level 3) Educator

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Polyphenol oxidase, or PPO, is common plant enzyme which is believed to play a role in the plant's ability to resist pathogens; in some plants it may also have a role in defense against damage by herbivores. PPO has been intensively studied by the food industry. When cell damage occurs, PPO is released and, as its name indicates, it oxidizes phenol compounds. The addition of oxygen causes monophenols to become linked into larger biphenols and polyphenols, many of which serve as pigments and cause the appearance of browning or bruising.

There are several ways cooks avoid browning of cut fruits and vegetables which, while harmless, is generally considered unattractive. One option is to keep oxygen away from the cut surfaces. Submerging the food in water or wrapping it tightly will accomplish this over the short term.

There are also ways to disable PPO. One is to adjust the pH; PPO works best at a pH of 6.0-7.0, and is completely disabled at pH levels below 3.0; hence many cooks will add lemon juice to cut fruits to reduce browning. The other option is blanching. To blanch a food, you must apply heat to the food for a very short time, and then cool it rapidly; the objective is to apply enough heat, in the form of steam or immersion in boiling water, to disable the PPO, but not enough to cook the food.  Proteins like PPO have complex folded structures, and the energy of heat will disrupt the folding and make the molecule nonfunctional; we call this process denaturation.

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