March 1998 -- Application By Lynn A. Kuntz
Editor Nearly everyone recognizes the relationship between a food's color and its appeal. Children seem to instinctively gravitate toward the most brightly colored candy in the store. Adults prefer their cheese crackers with a golden hue. Even the animal kingdom is not immune: birds know that the red of a strawberry signals a sweet taste treat, while the green ones are better left until another day. If, after the main ingredients have been combined and processed, they form a gray, unappealing blob, consider it a signal to modify the color to a more appealing hue. While the standard palette of FD&C dyes and lakes admirably addresses most food-coloring needs, it tends to suffer the "chemical" stigma that dogs many ingredients. In addition, studies and rumors linking certain certified colors, current and past, to ills ranging from cancer to allergies to hyperactivity, have contributed to their sometimes less-than-enthusiastic consumer reception. Therefore, interest continues to grow in the use of (so-called) natural colorants in foods.
First of all, let's make it perfectly clear that, according to the FDA, there is no such thing as an artificial, natural or even unnatural color. There are colors that are certified (commonly referred to by the unwashed hordes and many in the food industry as "artificial") and those that are exempt from certification (often called "natural," although certain ingredients do not even fit the definition of "natural" by the widest stretch of the imagination). The list of colors exempt from certification are listed and described in 21 CFR 73. The ones approved for food, rather than animal feed, include: annatto extract; dehydrated beets (beet powder); caramel; ß-apo-8'-carotenal; ß-carotene; cochineal extract and carmine; toasted partially defatted cooked cottonseed flour; ferrous gluconate and ferrous lactate; grape color extract; grape skin extract (enocianina); fruit juice; vegetable juice; carrot oil; paprika and paprika oleoresin; riboflavin; saffron; titanium dioxide; and turmeric and turmeric oleoresin.
A word from FDA
The CFR delineates any usage restrictions. Most are acceptable in all foods at levels consistent with good manufacturing practice as long as they don't have a standard of identity precluding their use. However, some are restricted to certain products (ferrous gluconate and ferrous lactate to olives; grape-skin extract to still and carbonated drinks and ades, beverage bases, and alcoholic beverages). Others have restricted levels (ß-apo-8'-carotenal limited to 15 mg per lb. of solid or semisolid food or per pint of liquid food; titanium dioxide limited to not more than 1% by weight of the food).
Other countries have different rules regarding the types of colors allowed, and their usage. For example, the European Union does not make any distinctions based on certification; all approved colorants receive a European Economic Community "E" number. Colors derived from natural sources approved outside of the United States include compounds such as anthocyanin, carbon black, curcumin, chlorophyll and lutein (from marigold). But usage rules vary widely. Restrictions in levels or product usage might be in force, and these may vary from nation to nation, even within the EU.
"If you go to Asia, you'll find that they consider synthesized ß-carotene an artificial color, because it is not derived from a natural source," says Per Isager, R&D manager, Chr. Hansen, Inc., Milwaukee. "In the U.S. and EU, it's still considered to be a natural color, although it is a synthesized product."There has been, and continues to be, industry and government discussion to widen the field of approved, noncertified color in the United States, particularly colors already enjoying wide use overseas. The biggest stumbling block is that manufacturers must petition FDA for a color's approval before it can be marketed. This will require all the usual supporting evidence required for any other food additive, including safety studies. FDA then must consider the composition and properties of the substance, the amount likely to be consumed, its probable long-term effects, and safety factors.
Under FDA regulations, any color added to a food product cannot be considered "natural," no matter what the source, according to Penny Huck, associate director of technical services, Warner-Jenkinson Co., St. Louis. That's unless the colorant is natural to the food product itself -- strawberry juice that gives strawberry ice-cream a pink hue, for example. If red beet color is used for strawberry ice cream, it would not be considered "naturally colored," because beet juice is not a natural component of strawberries or ice cream.
So, while the industry and the general public consider the "noncertified" colors natural, products cannot carry a label of "naturally colored" if they are used. Instead, they must use one of several options: "color added," "artificial color added," "colored with (name of noncertified color)" or "(name of non-certified color) color."Despite prohibition of the word "natural" on the label, product designers still gain advantages. "Many food companies have their own internal 'natural' policy," Huck says. "In addition, declaring a natural color by name on an ingredient statement is actually considered a plus for some companies -- the idea that a consumer may view annatto extract as more natural than FD&C Yellow No. 5 and FD&C Yellow No. 6."
In addition to a more consumer-friendly label, natural colors provide other advantages. They can yield hues unattainable with certified colors. This is particularly true in terms of golden yellow. Annatto excels at producing a tone that consumers recognize as cheese. The FD&C version tends to give a brighter hue that is more indicative of cheese curls than cheddar.
Natural whys and ways
"In addition, the physical properties of some colorants are not achievable with synthetic colorants," Huck points out. "For example, many natural colors are oil-soluble, whereas none of their certified counterparts are truly soluble in oil. Applications where this property would be important are oil-based salad dressings and popcorn oils."
FD&C lakes are often thought to be oil-soluble. However, they actually color by dispersion; they are insoluble in oil or water. An oil-soluble color, such as ß-carotene, annatto or paprika oleoresin, will solubilize throughout an oil-based medium. Adding the color to a fat-containing phase, like the creaming step for a bakery product, facilitates dispersion, ensuring even distribution.
Still, natural colors have some drawbacks when compared with the certified colors. They are typically more expensive. They require manufacturing, concentration and purification steps, and contain less pigment in a given volume. "Typically, we're limited (in actual pigment content) by what else comes out during the extraction process," Huck says.
Because they originate in nature instead of a lab, they are prone to more color variations than FD&Cs. This can be caused by a number of factors: growing conditions, variety and source of plant. "We use proprietary processes to obtain a range of colors, and then blend to a precise color target," says Edward Race, manager of technical services and R&D at Cananadaiga Concentrates and Colors, Madera, CA. "We standardize our products to an instrumental -- spectrophotometer -- color target. The specification sheets have the exact methodology, because with grape juice concentrates, pH is critical."
Visual-type analyses with colorimeters also can be useful to standardize colors. "When you mix extracts such as paprika, carmine and grape together, it's very difficult to get all the different pigments dissolved in one solvent, and get an accurate reading on a spectrophotometer," observes Carol Locey, color product manager, Kalsec, Inc., Kalamazoo, MI. "Therefore, an alternative color evaluation may be performed, such as a dispersion into a matrix that mimics the food. Ultimately, it's the appearance of the pigment in the food that is important."
Naturally derived colors have the reputation of being unstable, particularly in the presence of light, which accelerates degradative oxidation, or when exposed to the wrong pH. This isn't entirely true; titanium dioxide, caramel color and carmine are extremely stable to changes induced by these factors. In fact, carmine exhibits equal or better stability than some of the synthetics, according to Huck. Still, the pH influences the hue, the intensity and the stability of many of the naturals. Acidic conditions turn annatto pink. A pH over 7 causes turmeric to appear red and to fade rapidly. Metal ions, such as iron, copper magnesium and aluminum, can catalyze oxidative color loss in carotenoid pigments.
"Although many natural pigments are effective antioxidants, they are, themselves, prone to oxidation," says Locey. Protecting pigments from oxidation is one way to enhance their stability. "We developed the first paprika and annatto colors with increased resistance to oxidation. These colors are based on patented technology." She says that the products excel in applications such as seasonings and breadings or cheeses packaged in glass or clear film wraps.
Color loss often indicates a parallel deterioration in flavor. According to Locey, Kalsec has performed tests showing that off-flavor development may begin prior to a visual fading. "Our tests indicate that flavor deterioration is inhibited in a system using Durabrite(r) colors."
Another way to stabilize the color is by the use of special stabilization techniques, notes Isager. "We have examples of turmeric that have been exposed to the sun for a year-and-a-half, and they pretty much have kept their original yellow color," he says. "We originally developed this for the beverage industry, where the product is not only exposed to light but to low pH. But there are many more applications because of the advantages over traditional turmeric products. We also stabilize paprika, annatto and carmine, and for Europe, a chlorophyll, using the same process."
Because they aren't as reactive, products that are dispersed are generally more chemically stable than those that are dissolved in water.
Heat can affect the stability of some natural colors, including some carotenoids (though not annatto) and the anthocyanins. These should be added toward the end of the heating process, as late as practically possible to ensure adequate dispersion or solution.Many of these products naturally carry flavor, but some can be deflavorized during extraction. For example, capsicum, the flavor-producing component in paprika, is easily separated from the nonwater-soluble pigments. Some chlorophylls taste grassy. "Turmeric has a little bit of flavor," Isager says, "but that's carried by the pigment itself, and doesn't generally cause a problem."
Most natural colors are mixtures of numerous natural compounds. The main, plant-based pigments include the carotenoids and the anthocyanins. Caramel color depends on the products of carbohydrates subjected to heat.
Carotenoids are naturally occurring red, yellow and orange pigments. More than 700 carotenoids have been identified. They absorb light in the 400 to 500 nm region of the visible spectrum. Carotenes and lycopene are hydrocarbon carotenoids. Those containing oxygen, such as bixin (annatto), capsanthin (paprika), lutein (marigold) and zeaxanthin (corn), are classified as xanthophylls. Their concentration and ratio give a specific color.
In addition to their ability to impart colors to foods, a number of studies have conferred these compounds with potential health benefits based on their antioxidant properties -- not a bad bonus for a coloring agent.
Another group of compounds rising in esteem in health circles is the flavonoids, which count anthocyanins among their own. These are responsible for many of the blues, purples, magentas, reds and oranges. Although about 250 anthocyanins have been identified, only six are found in high levels in foods: perargonidin, cynaidin, delphinidin, peonidian, petunidin and malvidin. Varieties and concentration vary with type of plant, growing conditions and maturity. In addition, the color and its properties can vary, depending on the form the anthocyanins take. The colors produced by anthocyanins are strongly influenced by pH.
"We feel we get excellent stability from the natural pigments found in the ruby-red grape," Race says. "It contains a high level of malvidin 3,5 diglucoside, compared to Concord, which has a lot of monoglucosides and doesn't appear to be nearly as stable. The high tannin content also seems to have a stabilizing effect. Processing can polymerize some of the pigments, giving you different shades with the same pigment."
Betalaines, found in beets, are another class of naturally occurring pigments. The betacyanins are red and the betaxanthins are yellow. Unlike anthocyanins, the colors are stable to shifts in pH between 4.0 and 7.0. Betalaines are oxygen-sensitive, and light accelerates the degradation.
While nature makes an array of hues, including the greens produced by chlorophyll, no true greens or blues from natural sources are currently approved for food use in the United States. Chlorophylls have some pH sensitivity.
The blue-green algae known as spirulina cannot be used as a colorant in the United States. But if used as a nutritional additive, it may impart the characterizing color to a beverage or other nutraceutical. "Spirulina is the only true, blue natural color currently being commercialized," Isager says, "although there's a product derived from the blue gardenia flower, but that has more of a purple color."The pantheon of natural colors also includes:
Annatto. This yellow food colorant comes from the seeds of a tropical evergreen tree, Bixa orellana L. The pigments that produce the yellow to orange color range are the carotenoids bixin and norbixin. The concentration is expressed as percentage of one or both of these compounds. The norbixin content of an annatto cheese color ranges from 0.32% to 1.27%. "The more norbixin, which is the more water-soluble part of the two pigments, the more it shifts toward yellow, while the bixin tends toward the yellowish-red," observes Isager. The pigment content varies with the extraction and standardization method. Food-grade acids added to the alkaline, alcohol or aqueous extracts precipitate the pigments, which are separated from the liquid, and dried. Annatto can be prepared as water-soluble powder, water-soluble liquid, oil-soluble liquid or suspension in vegetable oil, or emulsion. Emulsifiers, pH and the overall solubility affect the hue; the greater the solubility in oil, the brighter the yellow color. Annatto is available in water-soluble, oil-soluble or oil/water-dispersible forms. To prevent annatto from precipitating or turning pink at a pH below 5, color manufacturers have developed acid-proof versions. "When working with annatto, you have to take into account its stability," Locey says. "Annatto is successfully used in many heat-processed foods such as aseptic cheese. However, excessive or prolonged heating can degrade the pigment. If this becomes an issue, we recommend adding the color toward the end of processing. Two other characteristics that affect the color hue and intensity achieved with annatto are its solubility and the pH of the food. Generally a more oil-soluble annatto provides a more yellow hue in snack foods and processed cheese. If the pigment is precipitated in the food, either due to low solubility or low pH, the hue will be more red." Beet juice. The juice or dehydrated juice from beets can produce a bluish-red color from betanin. The color is stable at a higher pH range than cabbage. Beet juice has no legal usage limit. But when used at high levels, it can contribute a characteristic beet flavor. "In some applications, especially dairy, red beet makes a good, cost-effective substitute for carmine," Isager notes. "However, the color from red beet will not survive a high heat process." ß-apo-8'-carotenal. This carotene typically is chemically synthesized and used to impart an orange hue. Like ß-carotene, it exhibits vitamin A activity, although it is not as pronounced. ß-carotene. This precursor for vitamin A contributes an orange-yellow color to food. Its antioxidant properties have been widely touted. Most ß-carotene is synthesized. It also is, according to Isager, "nature-identical." The substance also can be derived from algae. ß-carotene is oil-soluble, but can be made into a water-dispersible emulsion. Caramel color. The controlled-heating, food-grade carbohydrates -- generally a high dextrose-containing starch hydrolysate or corn syrup -- results in a brown coloring agent known as caramel color. Basically, the end result is caramelized sugar when the sugar molecule is broken down to furans and polymers with conjugated double bonds that absorb light and produce colors. Using catalysts can increase the reaction rate and create specific types of caramel colors with different properties.
Caramel color is water-soluble. Its color ranges from golden brown to nearly black. The color strength is defined as its tinctorial power -- the absorbency at 560 nm on a spectrophotometer, according to Sethness Products Company, Chicago.
The color tone, defined by the hue index, measures the red characteristics of the color, and is a function of the absorbency at 510 and 610 nm. Generally, the higher the tinctorial power, or strength, the lower the hue index, or red tones. The term "double strength," as applied to caramel color, is a relative term that varies with the color range. The specific gravity indicates the solids content and, therefore, the color strength.
Most caramel color carries either a positive or negative ionic charge. Negatively charged product uses sulfite in its manufacture and, though molecularly bound, it can be detected chemically. Because FDA requires sulfite labeling at levels greater than 10 ppm, the level in a specific type of caramel color may become important.
"Caramel color is stable under most conditions," says Owen Parker, vice president of research and development, D. D. Williamson & Co., Inc., Louisville, KY. "Certain caramel colors will darken slightly with a rise in pH. The lighter brewing caramels are more susceptible; with a darker caramel color the glucose or sugar is mostly used up so there is little to polymerize further and change. And if you dilute caramel color and expose it to direct sunlight or UV light it will eventually fade."Carmine/cochineal extract. Carminic acid, derived from the shells of dried female insects (Dactylopius coccus costa) is the main pigment in carmine or cochineal. Cochineal extract contains approximately 2% to 3% carminic acid. Depending on the product and the pH, it produces colors in the orange to purple range. Carmine is the salt of the pigment, which produces a magenta-red shade. The water-insoluble lake forms of carmine range from pink to purple, and will have carminic acid contents of not less than 50%. In order to stabilize carmine at low pHs, an acid-proof version is manufactured.
Since these colors aren't derived from plants, they may not be kosher-certified, although kosher versions are available. They also tend to be expensive compared to FD&C colors, although this may not hold true when comparing cost-in-use. Some reports indicate that some individuals might suffer allergic reactions to this colorant, probably due to the proteins present. However, carminic acid is extremely heat-stable. When used in a low pH beverage, it "yields a particular hue -- a bright magenta -- not achievable with certified colors," Huck says. "The only certified color alternative for this type of application, FD&C Red No. 40 dye, is more of an orange-red shade."
Toasted, partially defatted, cooked cottonseed flour. This colorant comes from food-quality cottonseed that is delinted and decorticated. The meats are screened, aspirated and rolled. The moisture is adjusted, and the meats heated. After the oil is expressed, the cooked meats are cooled, ground and reheated to obtain a product varying in shade from light to dark brown.
Ferrous gluconate and ferrous lactate. These compounds are defined in the Food Chemicals Codex, and are used for coloring ripe olives.
Grape-color extract. This consists of an aqueous solution of anthocyanin grape pigments made from the precipitated lees of Concord grapes or a dehydrated water-soluble powder prepared from the aqueous solution. It contains the common components of grape juice: anthocyanins, tartrates, malates, sugars, minerals, etc. The powder is prepared by spray-drying the extracted liquid with maltodextrin.Grape-skin extract. Also known as enocianina, this purplish-red liquid is prepared by the aqueous extraction of fresh, deseeded marc (after grapes have been pressed for grape juice or wine). It also contains the common components of grape juice -- anthocyanins, tartaric acid, tannins, sugars, minerals -- but not in the same proportion as found in grape juice. During the steeping process, sulfur dioxide is added and most of the extracted sugars are fermented to alcohol. The extract is concentrated by vacuum evaporation, during which time practically all alcohol is removed. A small amount of sulfur dioxide may be present. FDA restricts grape-skin extract to still and carbonated drinks and ades, beverage bases, and alcoholic beverages.
Fruit juice/vegetable juice. Fruit juice used as a colorant can be obtained either by expressing the juice from mature varieties of fresh, edible fruits or vegetables, or by water infusion of dried varieties. It may be used single-strength, concentrated or dried.
This category includes numerous products, but they must meet this definition. Being neither fruit nor vegetable, spirulina would fall outside of this definition.
High color with low flavor is preferable. Under the definition, spinach juice would be considered a vegetable-juice colorant, but the coloring strength is so low compared to the flavor level, that it's just about impossible to use. "Coloring pasta is actually done with dehydrated spinach powder," Huck says, "which technically does not qualify as a vegetable juice powder."
Most of the fruit products are high in anthocyanins. Grape, cranberry, chokeberry, elderberry and other berries have been used in this regard. The most commonly used vegetable dye -- red cabbage juice -- produces a bright pink-to-red color in a pH under 4. Higher pHs cause the anthocyanin-based pigments to turn an unstable purplish-blue color. These products dissolve in water, but not in oil.
Carrot oil. This is the liquid or the solid portion of the mixture or the mixture itself obtained by the hexane extraction of edible carrots. The hexane is removed by vacuum distillation. It consists mainly of naturally occurring oils, fats, waxes and the carotenoid pigments µ- and ß-carotene.
Paprika oleoresin. The oleoresin extracted from the pod of Capsicum annum, or paprika, primarily contains three carotenoid pigments: capsanthin (the main coloring agent), capsorubin and ß-carotene. However, as many as 20 or more pigments can be present, including zeaxanthin, which, with ß-carotene, produces a more yellow hue. "Most of the time, these different ratios won't have a visual impact," Locey says. "But, in some cases, they can make a difference. Hue control is maintained by raw material selection and blending."
Typically, paprika imparts a bright orange to red-orange color in food products. The oleoresin is oil-soluble, but when emulsified becomes water-dispersible.
"Color differences in paprika can be quite pronounced if you are looking at paprika from different sources," Isager says. "Paprika grows in Spain, Iraq, Zimbabwe, China and South America. This can give a wide variety of shades from yellow to a yellowish-red. Because we need to deliver a standard shade to our customers each time, that causes difficulties. Typically, we would select based on the color, and blend, if necessary, to a specific standard. Also, products using our special stabilization technique will not show the differences seen in the raw material -- another advantage of this product line."Riboflavin. Also know as vitamin B2, this is a group of compounds that produces a yellow to orange-yellow color, in addition to their vitamin activity. Saffron. This additive consists of the dried stigma of Crocus sativus L. It produces a bright yellow color, due to the natural pigment crosin, a water-soluble carotenoid. Because of its expense, it is rarely used in this country. Titanium dioxide. This synthetic compound provides white color and an opaque appearance. It is insoluble, but water- and oil-dispersible versions are manufactured. "Titanium dioxide tends to agglomerate and require high shear to fully and evenly disperse," Huck notes. "Because of this, food companies typically utilize a dispersion of titanium dioxide in a food-grade vehicle such as oil, propylene glycol, sugar syrup or water with select thickeners." Turmeric. This bright yellow colorant comes from the rhizome of an herb, Curcuma longa L. The pigments responsible for the color are curcuminoids. These include curcumin and related compounds, the same pigment used to color curry. This shade is compared to that produced by Yellow No. 5. Solubility depends on the medium in which the pigments are dispersed as well as the extraction process. Turmeric is insoluble, but a suspension of turmeric extract in oil can be added to fat-based systems such as margarine. At high pHs, turmeric turns orange-red. The properties of natural colors make them important tools in the design of a product. As related benefits, labeling advantages and functional properties become more widely known, they may become indispensable.