Processed: Food Science and the Modern Meal
In 1912 Louis Maillard was the first to describe the chemical reactions in grilled, sautéed, and baked foods that make them so delicious and, we know now, a little unhealthy. (Flickr user jypsygen)
Normally the Maillard reaction is described with appetizing adjectives, and rightly so. In 1912 French chemist Louis-Camille Maillard published a paper that describes what happens when amino acids react with sugars at elevated temperatures: the creation of many delightful flavors and odors, such as the smell of popcorn and the taste and flavor of roasted coffee. The Maillard reaction is also responsible for the brown of barbecued steak, baked bread, and soy sauce. (Maillard reactions differ from but are often mistaken for caramelization, which is a browning of sugars exposed to heat.)
“There wasn’t much of what you could call flavor chemistry before Maillard,” remarks historian Alan Rocke. “In the 1800s the German chemist Justus von Liebig published ideas about the importance of protein extracts of beef, and a lawyer, Jean Anthelme Brillat-Savarin, published heavily cited anecdotal ponderings on taste, but Maillard was the first to tackle serious food chemistry.”
The Maillard reaction proceeds through three thorny, intricate steps, which can each produce hundreds of different products. In addition, most foods have many different kinds of amino acids and sugars, creating a cornucopia of possible participants in the reaction.
Not until 1953 did the chemistry community get a handle on how all these flavor compounds could be produced, says food chemist Vincenzo Fogliano. That year a chemist at the U.S. Department of Agriculture, John E. Hodge, established a mechanism for the Maillard reaction. “Maillard discovered the reaction, but Hodge understood it,” Fogliano says.
Fortuitously, developments in gas chromatography and protein mass spectrometry that same decade permitted food scientists to measure Maillard products in food, notes Floros. From that point the food industry had the tools to control the chemistry of cooking amino acids and sugars, both to orchestrate the production of pleasing flavors and odors and to avoid the offensive ones. However, this task is complicated by the fact that the Maillard reaction can produce thousands of different molecules with even slight changes to temperature, moisture levels, or pH, says food chemist Thomas Hofmann.
Sometimes a Maillard product will be universally pleasant, such as the 2,3-butanedione found in popcorn and grilled steak. Other times a product that is desirable in some dishes is less welcome in others, Hofmann explains. For example, the compound 2-acetyl-1-pyrroline gives crusty bread and basmati rice a pleasant odor and flavor but produces a strange aftertaste when found in ultra-high-temperature pasteurized milk. Maillard reactions can also change the texture and consistency of proteins in food, making yogurt more gelatinous or cheese softer and creamier, says food chemist Thomas Henle. Then there are the negative products, such as the loss of vitamin C and B1 in Maillard reactions during cooking, states food scientist Cathy Davies. And there’s the production of acrylamide.
When Tareke and Törnqvis, the toxicologists in Sweden, were asked to examine the exposure of the sick construction workers to acrylamide, they did what any reputable scientists would do: they compared the levels of acrylamide in the sick workers to those in the general population. To their surprise they found unexpectedly high levels of acrylamide in the control group. Tareke was also simultaneously comparing acrylamide levels in wild animals and domesticated pets for her doctoral work, and to her further surprise found high levels in pets.
Given that a major difference between wild and domesticated animals is the amount of processed food they consume, Törnqvis and Tareke suspected that the acrylamide in the human controls might be attributable to their eating highly processed food. In 2002 they showed that processed food, especially potato chips but also common baked bread, did in fact contain acrylamide. Facing public outcry, food-industry associations banded together to fund research on exactly how the Maillard reaction led to acrylamide production and how it might be thwarted. One of the most promising techniques developed for acrylamide prevention is using an enzyme called asparaginase to break down the amino acid asparagine, says food scientist Monica Anese. Because acrylamide is created when asparagine reacts with sugar, removing the amino acid at the outset decreases acrylamide levels in the final foodstuff. Another strategy, she says, is to lower cooking temperature since acrylamide is produced under high heat. The downside is less browning of cookies and bread, an unpopular option with consumers.