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Vegetable-Based Colors
January 18, 2012 - Article

By R.J. Foster, Contributing Editor

The orange of carrots and  the reddish hues of beets and cabbages at the vegetable stand are familiar sights to consumers, so colors derived from vegetables give label-readers a sense that the color is "natural." In the regulatory realm of food colors, however, they're not.

In Title 21 of the Code of Federal Regulations (CFR), Part 73, FDA classifies colorants as “certified" (prepared synthetically) or “exempt from certification" (derived from agricultural or biological sources). The rules state that certification of these color additives are “not necessary for the protection of the public health, and therefore batches thereof are exempt from the certification requirements." Consumers often translate these classifications into “artificial" and “natural," respectively. But consumers, processors and regulators are not always speaking the same language.

The term “natural color" is commonly used in the industry by both color and consumer-product manufacturers, when in fact there is no legal definition for natural color. “It is sometimes assumed that all colors which do not have to be certified are natural," says Carol Locey, director of product management, colors,  Kalsec, Inc., Kalamazoo, MI. "This is not accurate. Beta-carotene, which is an exempt color, can be produced either by synthetic means or extracted from natural sources." 

These little pigments go to market

"The most popularly used exempt colors from vegetable sources are paprika, annatto, turmeric, carrot, black carrot, cabbage, radish and beet," says Locey.

Some of these are specifically defined in the regulations. For example, 21 CFR 73.345 defines “paprika oleoresin" as “the combination of flavor and color principles obtained from paprika (Capsicum annuum L.) by extraction, using any one or a combination of the following solvents": acetone, ethyl alcohol, ethylene dichloride, hexane, isopropyl alcohol, methyl alcohol, methylene chloride and trichloroethylene. It goes on to say, “Paprika oleoresin shall contain no more residue of the solvents listed in paragraph (a)(1) of this section than is permitted of the corresponding solvents in spice oleoresins under applicable food additive regulations" (21 CFR 170-189). Plain “paprika" is defined (Sec. 73.340) as “the ground dried pod of mild capsicum (Capsicum annuum L.)."

 The regulations also spell out whether they are approved for general food use, like paprika, or whether their use is restricted.

There is also a more general category called “vegetable juice color" (21 CFR 73.260). According to Rajesh Cherian, manager, application support, Roha USA LLC, St. Louis, this “is identified as ‘vegetable juice prepared either by expressing the juice from mature varieties of fresh, edible vegetables, or by the water infusion of the dried vegetable. The color additive may be concentrated or dried.’"

That means some vegetable substances may impart color, but might not be strictly defined as colors. Think green spinach pasta, for example. “Spinach extract generally used in industry is a solvent-extracted product from spinach leaves, Spinacia oleracea L., standardized for chlorophyll content using vegetable oils," says Cherian. “Approved emulsifiers are used to make water-soluble products. The product may not fall under the definition of vegetable juice color but can be classified as ‘natural flavor,’ according to 21 CFR 101.22."

Nature is not quite as precise as FDA, so natural vegetable extracts may have a somewhat variable content. However, the compounds responsible for creating the hues are generally known, and most ingredients are standardized for consistent color production.

For example, the major coloring components in spinach are chlorophyll a and b, and beta carotene. Anthocyanins are the principal colorant in red cabbage, red radish, purple sweet potato and black carrot extracts, according to Gabe Srouji, Ph.D., director of R&D and technical services, Sensient Food Colors, St. Louis. Beet root’s color, although similar to that imparted by anthocyanins, comes from a different family of compounds called betalains. Betacyanins yield red hues, while beta-xanthins provide yellow. 

Anthocyanins are, however, not the only crimson colorants in the garden. Red, orange and yellow hues can also be achieved using any of over 700 members of the carotenoid family. Beta-carotene, perhaps the most familiar carotenoid, can be used at varying usage levels to yield red, orange or yellow hues.  Tomatoes share their rich-red color in the form of lycopene. Annatto seeds yield an interesting pair of carotenoids: oil-extracted bixin and water-extracted norbixin. Better-known to consumers for seasoning effects, turmeric contains the carotenoids capsanthin and capsorubin that can provide a bright-yellow color, while paprika contains curcumin that can impart a yellow-orange tone.  

Extraction of colorants varies with solubility of the coloring compound being extracted. “Water-soluble natural colorants are extracted from the botanical source by water infusion," Srouji says. “Oil-soluble colorants are normally extracted with suitable organic solvents approved for food processing." Organic solvents typically utilized include hexane, acetone or ethanol, alkaline methanol, and water. 

Extracts are standardized to specific absorbance specifications using food-grade diluents, such as soybean oil, canola oil, propylene glycol and glycerin, according to Locey. Because most food colors are extremely concentrated, typical usage rates range from 0.001% to 0.50%.  And, while these colorants can be used directly in foods with proper mixing, she suggests they can also be pre-diluted in a liquid, or dispersed on a dry carrier prior to addition to the food. “For example, paprika oleoresin is commonly plated on salt along with oleoresin flavors to produce a dry seasoning that is added to meat, such as pepperoni," she says.

Colorant constraints

“Unstabilized vegetable-based colors can impact a product’s shelf-life, especially color stability, due to high sensitivity to pH," notes George Kean, Ph.D., director R&D, colors, Kalsec, Inc. "They are also sensitive to heat, light, ascorbic acid and metals. These may cause oxidation, leading to fading, browning and flavor changes."

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