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February 1st, 2010

Sometimes I wonder about you… oxidation

by Tim, 2 Comments »

Haven’t you wondered about oxidation? Like when your guacamole is starting to look like bean dip or your freshly sliced apples are turning brown? Or maybe you wondered why some dried fruits are brightly colored and others are not. Well, I wonder about those things.

Oxidation in fruit is just like rust on metal. Basically, there is an enzyme (polyphenol oxidase) present in the fruit that reacts with oxygen and browns the surface of the fruit. While oxidation can be unpleasant to eat (who wants to eat brown guacamole), and there may be some loss in nutrients, most nutritional value is not lost.

Several years ago I started to wonder about the dried fruits I was eating, I could taste something I didn’t like in them. I noticed that there were packages, both of bright orange apricots, and brown ones too. The difference: sulfur dioxide.

Many dried fruits have sulfur dioxide, potassium sorbate, or sodium benzoate added to prevent oxidation and help preserve the color and nutritional value. While there are many opinions, and “science”, some saying the preservatives are good and fine and others saying they cause long term side effects, for me, it just came down to taste. It was really that simple. I would rather deal with the oxidation than with the sulfur dioxide.

If you have ever had a dehydrator you learn ways to help preserve color and nutrients without the use of preservatives. For example, soaking fruits in a lemon or lime juice solution, blanching (which destroys the enzymes though), or limiting the exposure to oxygen. Certain fruits are excellent for drying as the nature of the fruit allows it to be protected by the skin and allow the nutritional value to stay intact… like grapes, plums or berries.

For guacamole, I like to wait till the end of preparing it and then seal the top with a thin layer of lime juice (instead of mixing in right away). Not only is the lime key in the taste, it also helps to prevent oxidation by reducing the ph on the surface of the fruit and inactivating the enzyme, and by sealing the top so it prevents air from touching the guacamole… it’s a double whammy. Usually I will then mix the guac right before it gets served.

Just like anything, I try to do my best to look at what I am buying. Especially since so many crops are sprayed with pesticides or herbicides. Also, like in this post, many dried products had additives like artificial sweeteners added. Why? Why do that? It is fruit. Of course, that was in Taiwan, but nonetheless, it is good to be aware of where your food is coming from and the practices used in growing it and preserving it. (I definitely do not always know).

So, while oxidation is inevitable and fine in many respects, such as in dried fruit, there are also times when you should be wary. I am soon going to wonder aloud, or maybe in print, about oxidation in fats and oils.

On a side note, saying dried plums sounds so much better than saying prunes, don’t you think? When you say prunes, it makes one think of nursing homes and bowel movements, but when you say dried plums it makes you think of Christmastime… or something like that. I like dried plums.