February 5, 2008

Cold Potatoes, Black Bananas

Some fresh produce does well when we stick it in the refrigerator. However, for other types of produce the refrigerator is a big mistake. Why?

Black Banana in Fridge vs Yellow Banana in Room Temperature

Photo: Pragmagraphr (flickr)

A banana's cell walls have no natural defense against cold, so they are ruptured by the low temperature. This allows a host of naturally occurring digestive enzymes to escape the cells. Banana quickly turns black and mushy.

Some fresh produce does well when we stick it in the refrigerator. Fruits and veggies like lettuce, apples, and oranges stay fresh even as the temperature approaches the freezing point.

For these produce items, low temperature works by slowing down the natural aging and decaying processes. However, for other types of produce the refrigerator is a big mistake. How come?

Bananas!

As you might expect, produce from the warmer, tropical climates tends to fare most poorly in the cold refrigerator. Bananas are a perfect example. A banana’s cell walls have no natural defense against cold, so they are ruptured by the low temperature.

This allows a host of naturally occurring digestive enzymes to escape the cells. These enzymes, normally controlled within the cell, go on a sort of rampage. They break down vitamins and other nutrients in the banana, quickly turning the whole fruit mushy and black.

Potatoes

Produce from colder climates can pose a totally different problem. Consider the potato. If potatoes are refrigerated, they don’t turn black and mushy, but they do turn sweet.

This is because inside a fresh potato two chemical processes are taking place. One is slowly turning the potato’s supply of starch into sugar, the other, called “respiration,” slowly burns that sugar.

Sugar And Sweet Potatoes

Normally, these processes are balanced; sugar is produced at the same rate it is burned. Inside of your fridge, however, it’s cold enough to slow down the respiration process, but the conversion of starch to sugar remains unchecked.

That’s why cold potatoes turn sweet. Interestingly, the same thing happens to carrots in the fridge. But, since we like our carrots sweet, we don’t see this as a problem.