Plastic Rap

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By Robert L. Wolke
Wednesday, March 30, 2005

In the March 2 Post Food section ("Hardware That Cooks"), I read that some restaurant chefs use PVC plastic pipe as a tool in molding foods. Isn't this dangerous? I've heard that the toxic plasticizer chemicals in PVC can leach out into the food.

Lately, there has been a lot of misunderstanding and mistrust of plastics in general and PVC in particular bandied about on the Internet. But here are some facts, which of course rarely inhibit the disseminators of Internet urban legends.

PVC (polyvinyl chloride) plastic can be manufactured in a variety of forms and used to make hundreds of different products. You can find it in the form of thin films used as food wrap in your kitchen, as thicker sheets from which your "vinyl" raincoat or handbag is made, in your garden hose and floor tiles and as the rigid, white pipes that deliver drinking water to your house and carry away sewage. Yes, PVC pipes are used to carry potable water. How's that for harmlessness?

Then why the fear of PVC in food use?

All PVC is not the same. Most of the difference between one kind and another is caused by chemical additives called plasticizers. Unmodified PVC is inherently almost rock hard, and plasticizers soften it for use in products requiring flexibility, such as food-wrap film and garden hose. The plasticizers, not the PVC itself, are the potential cause for concern.

The two major plasticizers used in PVC are di(2-ethylhexyl)phthalate (DEHP) and di(2-ethylhexyl)adipate (DEHA), which is a suspected carcinogen. It has been found that tiny amounts of DEHA can migrate from PVC plastic wrap into fatty foods that are in contact with it while being heated in a microwave oven. But even though I don't think I'll die from reheating an occasional leftover, I take the precaution of covering my microwaved foods with an inverted paper plate rather than plastic wrap. That's because food-wrap manufacturers don't tell us which plastic their wrap is made from, and I never know which ones are PVC. However, they're often the soft, stretchy ones.

At the other end of the PVC hardness spectrum is PVC pipe. It is made of hard, rigid PVC that contains no plasticizer. What isn't there cannot leach out into food. So clean, room-temperature PVC pipe can be used as a perfectly safe food utensil.

And that's a fact.

In the Post's story on lentils (March 2), it was stated that one needs to add meat, dairy or grains to supplement the lentils' incomplete protein. Vegetarians and vegans claim they can get all the protein they need without eating any of these other kinds of foods. Who's right?

I'm a chemist, not a nutritionist, but proteins are made of amino acids, and I know an amino acid when I encounter -- or don't encounter -- one.

"Complete protein" can be fightin' words. That expression is based on the idea that, while our bodies can manufacture about a dozen of the 20-or-so amino acids that are the building blocks of proteins, we must get the rest of them (the so-called "essential" amino acids) from foods. A food containing "complete protein," then, is theoretically one that gives us all the essential amino acids, ready-made.

That's a nice, straightforward concept. But ask, for example, whether lentils contain complete protein and the battle begins. It just isn't that simple. There are 10 traditionally cited essential amino acids: arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine, although two of them (arginine and histidine) are essential only for growing children. But it's all a matter of amount. How much of essential amino acid "x" does a food have to contain before we say it "contains amino acid x"?

According to the U.S. Department of Agriculture's Nutrient Database for Standard Reference, lentils contain some of all 10, but only very small amounts of methionine and tryptophan (0.24 and 0.25 percent, respectively). So does that make a complete protein? Take your stand and defend it.

Nutritionists talk about the "limiting amino acid" in a food: the essential amino acid present in the smallest amount. In legumes, it's methionine; in wheat, it's lysine; in rice, lysine and threonine; in corn (maize), tryptophan and lysine; and in beef, methionine and cysteine. Every source of protein has its assets and deficits.

How, then, are people to get their complete protein? By eating a varied diet, with or without animal products. Contrary to common belief, all the essential amino acids don't have to be combined in the same mouthful, or even in the same meal. You do intend to eat again, don't you?

LABELINGO: A group of perspicacious readers who identify themselves as the "Astute Science Department" at Centreville High School in Clifton were amazed to find silicon dioxide listed as an ingredient in Nu-Salt, a salt substitute consisting mainly of potassium chloride. "Holy Cow!" they chorused. "Does this mean we are eating sand in our Nu-Salt?"

Yes, you smarties who know that sand is made of silicon dioxide. In a way it does mean that. But in Nu-Salt (and other salt products), it is present as a small amount of very fine powder, which absorbs moisture and keeps the product flowing freely. It traverses the entire alimentary canal and emerges unscathed.

(Have you noticed any silly things on food labels? Send your Labelingo contributions, along with your name and town, to Food 101, Food Section, The Washington Post, 1150 15th Street, N.W., Washington, D.C. 20071 or via e-mail to wolke@pitt.edu. )

Robert L. Wolke is professor emeritus of chemistry at the University of Pittsburgh. His latest book, "What Einstein Told His Cook 2: Further Adventures in Kitchen Science," will be published by W. W. Norton this month. He can be reached at wolke@pitt.edu.


© 2005 The Washington Post Company

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