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August 25, 2003
Volume 81, Number 34
CENEAR 81 34 p. 34
ISSN 0009-2347


Synthetic and natural additives impart a rainbow of possibilities to the foods we eat


TONGUE-DYED Water-soluble food colors can temporarily stain tongues, lips, and teeth.
I have a friend who won't eat anything blue. Fresh blueberries are okay, but just watch her cringe at the neon blast of a blue raspberry Icee or the sapphire wiggle of a bowl of berry-blue Jello.

Students of color psychology would say that my friend is reacting as nature intended. Aside from blueberries, how many naturally blue foods can you count? In contrast, just try listing all the fruits and veggies that mature into lovely shades of red or yellow. Blue, it would seem, is just not a part of nature's appetite-inducing palette.

Color plays such an important part in how people respond to food that almost anything found in a modern grocery store has a dash of something to enhance eye appeal. That something can be natural--the caramel color in most cola really is heated sugar--or synthetic--petroleum-based azo dyes such as 6-hydroxy-5-[(2-methoxy-5-methyl-4-sulfophenyl)azo]-2-naphthalenesulfonic acid, otherwise known as FD&C Red No. 40.

No matter where it comes from, any color added to our food is carefully regulated by the Food & Drug Administration to ensure it is safe to eat and is correctly labeled. In fact, color additives are probably the most highly regulated food ingredient, says David Frick, global technical resource manager at Sensient Technologies, which bills itself as the world's leading manufacturer of high-purity, regulated colors for the food industry.

According to Frick, FDA regulates colors based on their end use--food, drugs, cosmetics, and medical devices--and food colors are divided into two broad regulatory categories: certifiable and exempt from certification. Certifiable colors encompass the synthetics that have no natural counterparts. FDA lists only seven approved colors for general food use, and each batch of a certifiable color must be tested by FDA before it is approved for sale. The color can then be labeled as FD&C, meaning it is ready for use in food, drugs, or cosmetics.

FD&C colors can be either dyes or lakes, depending on their solubility. "Dyes by definition are colors that have to be dissolved to function," Frick says. Lakes, on the other hand, are a way of making soluble dyes insoluble, usually by adsorbing a dye on a substrate of alumina hydrate. Lakes are typically used in products that don't have enough moisture to absorb the dye or where the potential for dye migration would be a hindrance. Examples include oil-based products such as frosting, direct compression items such as chewable vitamins, and coated candies such as M&Ms or Skittles.

Colors derived from or based on natural sources are categorized as exempt from certification and don't have to undergo FDA batch testing, Frick says. Exempt colors come from plants, fungi, and even insects, but they can also be the synthetic versions of biobased compounds. For example, -carotene, known for lending its yellow-orange hue to carrots, is almost always a lab-created chemical when found in products on grocery store shelves.

Although they don't have to be certified, the dyes that come from living matter are processed under strictly controlled conditions and are held to very high standards of purity. According to literature provided by Sensient, a major ingredient in the bitter Italian liquor Campari is an exempt dye called carminic acid. This vibrant magenta additive originates from the dried, crushed bodies of pregnant female scale insects called cochineal [Dactylopius coccus costa (Coccus cacti L.)]. Incas and Mayas used these prickly pear parasites for centuries as a dye source, and they were brought into Western markets by Cortez in the 16th century. Today, most cochineal is harvested from managed cactus plantations in Peru and the Canary Islands and is processed in food-grade facilities.

Dried cochineal contains 17 to 24% carminic acid, an anthraquinone that most of the insect's predators find unpalatable. In modern processing methods, carminic acid is extracted from cochineal using an aqueous, alcoholic solution. It can then be used directly as a dye or precipitated on an aluminum hydroxide substrate to make carmine lake.

As it turns out, FDA has not approved a natural source of blue food dye. Even anthocyanins, the compounds that give blueberries their namesake shade, are not really blue. "Outside of the fruit, the chromophores are fairly stable as a red color. Inside the fruit, they orient themselves and associate with other compounds such as flavonoids, proteins, tannins, and other polyphenols to produce a blue," Frick says. Surprisingly, FDA is also lacking an approved natural source of green coloring. The most commonly known green pigment, chlorophyll, is allowed only in drugs or cosmetics--and then only at levels below 0.1%.

Currently, any blue or green food on the U.S. market gets its hues from certifiable colors FD&C Blue No. 1 (Brilliant Blue), Blue No. 2 (Indigotine), or Green No. 3 (Fast Green). Blue No. 1 and Green No. 3 are both petroleum-derived triphenylmethanes--that is, they have three aromatic rings attached to a central carbon atom. Blue No. 2 is a disodium sulfonate of a naturally occurring compound called indigo. However, the indigo used to create Blue No. 2 is synthesized by fusing N-phenylglycine in a molten mix of sodamide and sodium and potassium hydroxides.

Maybe my friend's aversion to blue food is a subconscious reaction to its unnatural origins. But then, in reality, most of the foods that she presumes are "all-natural" likely contain chemicals put there by the food industry. After all, even dyes extracted directly from biomass can't legally fall under the moniker of "natural color."

"If strawberry ice cream is colored with strawberry juice, you can make an argument that it is naturally colored," Frick says. "But if the ice cream is colored with beet juice, its color cannot be labeled as natural."


Chemical & Engineering News
Copyright © 2003 American Chemical Society

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