Tuesday, February 12, 2008

The Healthiest Onions

Read It And Weep

Onions are a very healthy food. If you study cultures and lands that regularly consume onions and garlic, you will find that they have lower rates of chronic diseases, including cardiovascular disease and cancer. I try to incorporate garlic and onion, as well as their elegant cousin, the shallot (Allium ascalonicum), a small but subtly flavored relative of the onion, into my diet whenever possible.

But, as you may have noticed, there have been changes in the onion business that bear watching. I went to the grocery last night and noticed that the price of onions has been on the rise. Where I used to pay 39 cents per pound, the price has jumped to over a dollar a pound! Shallots are $4 per pound. The "Sweet" varieties like the Vidalia onion used to be novel and more expensive. Now they are running at less than a dollar a pound.

Originally, the only variety of sweet onion available in most markets was a form of yellow granex known by the name Vidalia. Traditionally, these were harvested in southeast Georgia from late April till mid-June and were available only during the summer months. Now the Vidalia season has been extended for several months by use of controlled atmosphere (CA) storage. The principal characteristic of CA storage is a modification of the atmosphere in the storage facility. This involves decreasing the oxygen content of the air to 3 percent and maintaining the onions at a temperature of 34 degrees Fahrenheit. So there are now Vidalia and other sweet onions available in many markets year-round.

Vidalia onions have a very mild taste and do not make your eyes water when you cut them up. In time Vidalia was joined on the shelves by other varieties of sweet onions - Maui, Walla Walla, and Maya. These are all delicious. Some are available all year long and at 50 percent lower cost than standard yellow or red onions.

Chemical analysis has shown that the reason that these onions are so sweet is because of a lack of sulfur in the soil in the particular counties in which they are grown. Sulfur is necessary to produce the characteristically sharp taste and odor of typical onions. But therein lies the problem. Do these sulfur-lacking sweet onions convey the same health benefit as typical sharp onions? After all, we also know that sulfur is involved in the production of some of the very phenolic and flavonoid compounds that give the onion family its health benefit. (I am thinking in particular of organic allyl sulfur, the most desirable compound in onions and garlic.)

This question has been answered by food chemists at Cornell University and the results will not come as welcome news down in Jeff Davis County.

These Cornell scientists, led by Dr. R.H. Liu, compared the phenolic and flavonoid content of 10 varieties of onion that are commonly available in the United States, as well as shallots. The ten varieties were as follows:

1. Empire Sweet
2. Imperial Valley Sweet; and
3. Mexico
4. New York Bold
5. Northern Red
6. Peruvian Sweet
7. Texas 1015
8. Vidalia
9. Western White
10. Western Yellow

These were evaluated for their total phenolic and flavonoid content as well as their antioxidant and antiproliferative (i.e., anticancer) activity. Shallots had the highest total phenolic content among all the varieties tested, with a 6-fold difference observed when compared to Vidalia onions. Western Yellows exhibited the highest total flavonoid content of all the onion varieties tested, with an 11-fold difference when compared to the phenol-poor Western Whites. Shallots exhibited the highest total antioxidant activity.

Leaving aside the antioxidant-rich shallots, the onions were ranked as follows for antioxidant activity:

1. Western Yellow
2. New York Bold
3. Northern Red
4. Mexico
5. Empire Sweet
6. Western White
7. Peruvian Sweet
8. Texas 1015
9. Imperial Valley Sweet
10. Vidalia

The Cornell scientists also exposed various cancer cell lines to these onion varieties to see what effect the onions had on cell proliferation. The most effective of all in inhibiting cancer cells were - again - shallots, followed by New York Bold, Western Yellow and Northern Reds. The rest of the varieties all demonstrated weak anti-proliferative activity against these cancer cell lines. "These results may influence consumers toward purchasing onion varieties exhibiting greater potential health benefits," the authors wrote.

I know these results will influence my own shopping habits. The next time I purchase onions I will be looking for Western Yellow, New York Bold and/or Northern Red (a particularly good variety for salads). I will also get some shallots when my budget can afford them and they look nice and plump. Sweet onions, such as Vidalias or Maya, are indeed delicious and relatively inexpensive. But they simply do not convey a fraction of the health benefits of yellow or red onions, or of shallots.

1 comment:

cube said...

Good post. I recently went back to yellow onions from Vidalia because of price. It's good to know they're more healthy.