A closer look at fruit ripening

BURNING QUESTION

July 02, 2008|By Erica Marcus | Erica Marcus,NEWSDAY

Which fruit ripen after they are picked - and why?

For the lowdown on ripening, I called the postharvest information center at the University of California, Davis (postharvest.ucdavis.edu) and the California Tree Fruit Agreement (eatcaliforniafruit.com).

Ripening, I learned, is a complex process involving three changes in fruit: Starch is converted to sugar; acidity levels decrease, and the cell walls of the fruit begin to break down, making the fruit soften. Not every fruit experiences all these changes, but all of them experience at least one.

Climacteric fruit ripen after they are picked; nonclimacteric fruit do not. Nonclimacteric fruit include pineapples, cherries, grapes, citrus fruit, berries and watermelon. If they are not picked ripe, they never will ripen.

Climacteric fruit are themselves divided into two subcategories - those that get sweeter as they ripen and those that do not. What makes the difference is the presence, or absence, of starch reserves.

When a climacteric fruit with starch reserves ripens, the starches are converted into soluble sugars (sucrose, fructose and/or glucose), and the fruit gets sweeter. A climacteric fruit that has no starch reserves will pretty much only soften.

We are all familiar with fruit that get sweeter as they ripen on the counter: bananas, pears, kiwis and mangoes are the most common.

The prima donnas of the fruit world are those that soften after they are picked but do not become appreciably sweeter. In this group are peaches, nectarines, cantaloupe and honeydew. The moment they are separated from the tree, they are at their maximum sugar level.

Erica Marcus writes for Newsday.

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