Of Bamboo and French Fries

February 22, 2007 at 11:23 am

Chinese scientists report finding a way to diminish the development of acrylamide—a potential carcinogen—in baked and fried foods: Dip them in an extract of bamboo leaves prior to cooking. It’s the newest of several experimental approaches to limiting acrylamide in foods.

Soaking potato pieces in a bamboo extract prior to cooking can limit the development of acrylamide—a potential carcinogen—in french fries. Artville

Nearly 5 years ago, reports by Swedish scientists catapulted acrylamide to public attention around the world. The researchers found that high-temperature cooking, baking, or frying of a range of foods could induce one or more chemical reactions that generate acrylamide (SN: 5/4/02, p. 277). Topping the list of affected foods were many dietary staples: breads, crackers, breakfast cereals, cookies, and even french fries.

Prior to the Swedish team’s work, acrylamide had been known solely as a synthetic chemical used for purifying water and making some plastics. Commercial users handled acrylamide carefully because studies had shown that at high doses the chemical is a moderately potent carcinogen in rodents.

Once the team found high concentrations of the chemical lacing bakery goods and fried foods, many chemists began trying to answer how the chemical got there. The scientists soon homed in on the amino acid asparagine and some simple sugars, such as glucose, as possible culprits in the process (SN: 10/5/02, p. 213). How much acrylamide formed from interactions between these building blocks depended on cooking times and temperatures.

In 2000, Ying Zhang of Zhejiang University in Hangzhou, China, and his colleagues discovered that a bamboo extract has potent antioxidant properties. That is, it could spare DNA, fats, and cholesterol-ferrying lipoproteins from oxidative reactions that damage these materials and in some cases render them harmful. On the basis of such findings and analyses of the new antioxidant’s safety, China has listed the “solvent-extracted bamboo-leaf extract”—a complex of chemicals including chlorogenic acid, caffeic acid, and luteolin-7-glucoside—as a government-approved food preservative.

When Zhang’s group learned that other researchers had shown that antioxidants could cut acrylamide production by half or more in some cooked foods, Zhang and his colleagues decided to explore how their bamboo extract stacked up.

In the Jan. 24 Journal of Agricultural and Food Chemistry, they report that soaking raw potato pieces in a solution containing powdered extract cut by 75 percent the development of acrylamide in french fries and potato chips. The Chinese researchers say that the bamboo-derived chemicals don’t change a food’s flavor. They note that other potential acrylamide-fighting food additives haven’t yet been tested on that score.

Other options

Last year, A Swiss team reported that carefully controlling the heating and moisture content of some foods offers a way to limit acrylamide formation.

Thomas M. Amrein and his colleagues at the ETH Institute of Food Science and Nutrition in Zurich showed that more acrylamide forms during the cooking of relatively dry food ingredients—those containing less than 20 percent water. In potatoes, the researchers reported, most acrylamide formed in the late stages of frying—especially at a high cooking temperature.

These data explain why “a lower temperature toward the end of frying reduces the acrylamide content” without sacrificing the golden color consumers desire, Amrein’s team reported in the Aug. 9, 2006 Journal of Agricultural and Food Chemistry. How low a temperature? The researchers’ data showed that less than a tenth as much acrylamide forms at 119°C as at 167°C.

Almost a year ago, a Belgian team reported finding that certain potato varieties are more vulnerable to acrylamide production during french frying because the concentration of certain simple sugars, such as glucose and fructose, were unusually high in those varieties.

Moreover, Bruno De Meulenaer of Ghent University and his colleagues reported in the March 22, 2006 Journal of Agricultural and Food Chemistry that fries from potatoes less than 50 millimeters in length or width “were more susceptible to acrylamide formation and should be avoided.” The team explained that, all things being equal, small potatoes tend to contain significantly more simple sugars per unit weight than do larger spuds.

Finally, a European group headed by Erland Bråthen of the Norwegian Food Research Institute showed that enriching breads with either of two amino acids—glycine or glutamine—reduced acrylamide’s formation during baking by 50 to 95 percent, depending on the additive’s concentration and the type of bread made.

Soaking potato slices in a weak solution of either amino acid reduced acrylamide in potato chips by 45 percent. The effect climbed to roughly a 70 percent cut in the potential carcinogen if the potatoes were soaked briefly in a hot water bath containing the amino acids. Alas, soaking raw potatoes sliced for french fries had no effect on acrylamide in the final product.

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