Everything You Always Wanted to Know about the Maillard reaction… But Were Afraid to Ask!

zarkovEver since Prometheus brought fire to mankind and cooking began, humans have enjoyed the results of the Maillard reaction; without it cooked or fermented foods would lack much color and taste. But the reaction has a dark side, and causes deterioration of the body.

Beer, Food & Chemistry

In 1908, the English chemist A.R. Ling was trying to explain how beer obtained its color. He deduced that the reaction involved sugar and protein, but was unable to determine the precise mechanism. Across the English Channel, the French chemist Louis Camille Maillard was investigating how individual amino acids linked together to form proteins. (Proteins are just long chains of amino acids glued together and then folded into compact shapes.)

Maillard discovered, in 1912, when he combined sugar and amino acids in water and then heated the mixture it turned a yellowish-brown. This was the first time anyone was able to initiate nonenzymatic browning using well-defined materials.

When people talk about the Maillard reaction, they often to use the word “sugar” to mean either sugars or carbohydrates.

In honor of his discovery, the process binding a sugar to an amine, amino acid, peptide, or protein is known as the “Maillard reaction.” Familiar to chefs for centuries, it was not until 1953, however, that the complex web of underlying reactions was finally deciphered.

Why the Maillard Matters

The reaction is of crucial importance, and not just in chemistry. Crosslinking between sugars and amino acids, among others, produces much of the color and taste we associate with cooked or fermented foods. More ominously, crosslinking also forms many mutagenic, carcinogenic, and otherwise toxic compounds.

The very same reaction occurs in the body, as the proteins making up collagen, muscle tissue, bone, organs, eyes, etc. are hardened, distorted, corrupted, and otherwise rendered nonfunctional by sugar. Understanding the Maillard reaction leads not just to safer – and tastier – food, but also to longer, healthier living.

What Happens

A chemist explains the reaction as one of the reactive carbonyl groups in the sugar molecule binding with the amino acid’s nucleophilicamine group, yielding a variety of interesting, and frequently uncategorized, low-molecular weight organic compounds.

This is just a fancy way of saying that sugars and amino acids shuck off their shoes and join together permanently, forming new molecules, in a variety of small sizes, each with different chemical properties. The end products of the reaction, called “melanoidins,” have different colors and tastes, and have such variety that many have never been categorized, let alone studied.

What’s All That Brown Glop?

The brown residue left over after sauteing meats, commonly used to make sauces – aka “deglazing the pan” – is concentrated residue from the Maillard reaction.

So are: the color and taste of roasted coffee and cocoa beans; the crunchy, browned surface of toast; the caramelized tomato and sugar hybrids in barbeque sauce; the sweet, rich taste of roasted vegetables and caramelized onions; the crunchy goodness of creme brulee; the sticky, brown caramel formed when milk proteins and sugar combine; the taste and color of whiskey and beer; and even artificial maple syrup.

Yuck! That Smells & Tastes Bad!

The Maillard reaction, however, isn’t always pleasant. During World War II soldiers complained that powdered eggs were an unappetizing brown and tasted spoiled. This was of great concern to everyone since an army marches on its stomach.

Investigation showed that the eggs were dehydrated and stored at room temperature, which should have made them quite stable. It turned out that the egg’s sugars were reacting with the amino acids in the proteins and creating some most unpalatable results.

Only after a fermentation process was adopted to eliminate glucose from raw eggs did the powdered version finally obtain a shelf life beyond a few weeks.

Smile for the Camera!

A related problem exists with old photographs. More than eighty percent of 19th-century photographs are “albumen prints” using an egg-white fixative. These prints have yellowed, in what is now known to be a Maillard-based process identical to the spoiled powdered eggs during WWII.

For a long time, scientists and food experts focused solely on shutting down the Maillard reaction in food to prevent exactly this sort of spoilage, but quickly realized the potential for improving both food and food safety.

Cooking Up Taste or Trouble

The flavors and aromas used by the food industry; about half depend upon the Maillard reaction.

Literally thousands of different results depend upon the raw ingredients and how they are cooked together: a dozen types of carbohydrates or sugars (ranging from simple to complex, including fructose, glucose, lactose, maltose, maltotriose, pullulan, sorbitol, starch, sucrose, and trehalose); twenty different amino acids; a variety of reaction temperatures, a wide spectrum of pH (acid or base); and variable reaction times.

For example, dry-toasting malt for beer yields a cereal flavor whereas heating wet malt delivers more of a caramel taste. The raw ingredients are identical; the only difference is the amount of water. The flavors we associate with meat, nuts, coffee, and even chocolate originate with pyrazines and guaiacols containing nitrogen,oxygen and sulphur groups. Not very glamorous, perhaps, but chemistry deals with explanations, not poetry.

The melanoidins may have unpleasant flavors or odors – bitter, burnt, or rancid – or pleasing ones like bread, caramel, malt, or roast meat. The same goes for a wide range of colors; from Maillard’s original yellowish-brown to nearly pitch black.

No Oven Needed

The surfaces of roasted meats undergo extensive Maillard reactions because of exposure to high temperatures. The interior is largely unchanged because it is cooler, and the reaction proceeds far too slowly to yield significant results during the short cooking time. Low sugar levels and high water concentrations in the interior also slow down the reactions.

While the Maillard normally occurs above 285°F (140°C) – as in an oven or on a stove – it does occur at room temperature, only slower. This is why beer browns, pasta darkens during drying, and human tissue crosslinks, all at relatively “cool” temperatures. These cooler reactions take weeks or months instead of minutes, but they do occur, just the same.

Other Uses

Artificial tanning solutions, such as dihydroxyacetone (DHA), react with the arginine in the stratum corneum, the outermost layer of skin. The result is a brown “tan” at room temperature, with the darkness determined by exposure. Such tans are purely cosmetic since they have only minimal UV blocking effects.

Soybeans for cattle feed are now treated with a Maillard process to enhance digestibility and nutritional value.

Role in Diabetes & Aging

An article in this issue (“Aging is Just Diabetes, Only Slower”) explains how damage from aging and diabetes is directly attributable to Maillard crosslinking. The basic problem is sugar bonding to proteins and ruining them.

Conclusion

Understanding the Maillard reaction improves food’s taste and color, increases food safety, and provides ways to slow down or undo the effects and damage caused by aging and diabetes. Maillard’s discovery is thus still important and highly relevant more than one hundred years later – even if you don’t cook!

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