The Best Defense May be a Good Onion

There’s supposed to be a worldwide shortage of onions this year, but I don’t think anyone told my garden. This spring, onions were one of the only plants to survive in my slug-besieged community plot at the Experimental College. We had luck with garlic, chives, and arugula too, but our red onions were the standout. Originally, we put them in as a pest deterrent; now, they line the perimeter of each bed like a green picket fence.

An easy-to-thwart fence, it would seem. Leafless kale, skeletal collards, mowed-down brussels sprouts: within days newly planted greens were devoured. The interiors of our beds looked like the “before” picture in a pesticide commercial. One day, my husband picked slugs off seedlings for half an hour—he lost count after 70.  We eventually erected fully enclosed bed-coverings out of wood and mosquito netting, but our onions survived the gastrapodian onslaught cage-free. They thrived, along with every other pungent smelling, peppery tasting plant in the garden.

Garlic (Allium sativum) and chives (Allium schoenoprasum) belong to the same lachrymal inducing, chemical-producing taxonomic family as onions (Allium cepa). This family’s volatile sulfur-containing compounds act as a potent defense system—they convince pesky herbivores to dine elsewhere, and impart the onion’s characteristic smell and taste. When an onion’s cells are damaged (say, by a sharp knife, or a slug’s mouth), enzymes called alliinases escape and convert odorless precursors to pungent aromatics.

Wondering how to avoid tears? The main strategies fall into two categories: 1. Reduce gas-to-eye exposure. (Chopping onions underwater can help, as can wearing protective eyewear. If you Google “onion goggles” the first hit is a pair from Amazon. It’s described as “stylish and comfortable.” You be the judge.) 2. Reduce alliinase activity. (Alliinases are less active when cold, so cooling the onion before cutting results in less gas formation.) Onions, however, are able to stymie more than garden slugs and teary-eyed chefs. Recent research suggests that they might be able to keep bacteria at bay as well.

Scientists at the University of Barcelona tested the antimicrobial activities of three different varieties of onions against a panel of pathogenic microorganisms that cause food spoilage. They chopped, freeze-dried, then ground white and yellow onions to a fine powder, extracted the non water-soluble portion, and added the extract to six common strains of food borne bacteria. Why the non water-soluble part? The researchers wanted to isolate the onions’ flavonoids, an anti-oxidantcontaining class of plant compounds that has gained commercial notoriety due to one of its more popular members: quercetin.

You can buy quercetin in the form of a supplement (confession: we have a bottle at home—my husband couldn’t resist), or a Lance Armstrong-endorsed energy drink (FRS: Free Radical Scavenger. Tagline: “Healthy Energy.”’ Only $35.75 for 15 cans.), but if you eat berries, grapes, leafy greens, or onions, (among other fruits and vegetables) you’re already getting it in your diet.  What’s all the hype about? Flavonoids have long been reported to have a slew of beneficial healtheffects, from antiallergenic to anticarcinogenic to cardioprotective.

Antibacterial and antifungal properties are also among their arsenal of purported tricks.  Indeed, the University of Barcelona scientists confirmed that flavonoid-containing onion extract prevented growth of several strains of bacteria.  Not surprisingly, varieties with higher levels of flavonoids were able to inhibit a wider variety of bacteria. (Red onions weren’t tested in this study, but they’re also thought to be a rich source of flavonoids.)

So, good news for people who cook with onions: It’s likely that you’re getting protection for your leftovers, and maybe even protection for your body (not to mention a free dose of “Healthy Energy”).  Other common kitchen spices have also been implicated in food preservation.  Cloves, cinnamon, oregano, and thyme all contain flavonoids or other antimicrobial compounds that allow them to act as so-called “botanical bacteriocides.” These natural preservatives could serve as an alternative to artificial means of food preservation.  As for my garden, I’m starting to think attempting to grow greens was the wrong approach to winter food
production; next year I’m planting rows and rows of onions…maybe I can sell them to Lance.


~ by Meghan on July 23, 2010.

3 Responses to “The Best Defense May be a Good Onion”

  1. Meghan,
    Your mom just sent me a link to your blog. I love it! (My husband John and I are also NPR junkies.) Keep up the good work!
    Colleen Warner, Phoenix, AZ

  2. Great website, pls contiune your work and keep us update with more storys

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