Explain how blanching affects the enzyme, polyphenol oxidase, to stop the browning process.While watching a cooking show, you learn that the...

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.