The commercially available colorants typically fall into two general categories: liquids and powders. The liquids are either oil-soluble/dispersible or water-soluble/dispersible. The powders can be dried either via freeze-drying, spray-drying or tray-drying, or they can be microencapsulated versions of oil-soluble/dispersible colorants.
Until recently, production processes for plant-derived colorants often involved extraction with approved chemical solvents, followed by purification and concentration. Although the solvent method continues and provides less-expensive products, consumer demand has led many color creators to shift to direct expression of the plant juice, followed by physical and mechanical purification and concentration. There always has been a category of colorants that could be designated on labels as “fruit juices” or “vegetable juices.” These categories have become much more significant in recent years.
Generally, natural food colorants can be divided into functional categories based on their molecular structure. As a bonus, those chemical structures often go hand-in-hand with a biological function that served the original purpose and translates to healthy benefits for the consumer. Put simply, botanically derived colorants in nature help protect the plant with powerful antioxidants and other phytochemical compounds. This offers the advantage of bringing together colorants with similar functionality in application.
The most commonly known categories of natural colorants with that extra touch of health are the carotenoids and the anthocyanins. In the carotenoid family, the most familiar member is beta-carotene. Beta-carotene has been popularized for its purported health benefits. It is a vitamin A precursor, which means it is converted into vitamin A in the body. It is also a fairly good antioxidant, as are most carotenoids. A partial list of carotenoid colors includes beta-carotene, lycopene, annatto bean, saffron, astaxanthin, lutein and paprika.
These products are mostly oil-soluble materials that can be rendered water-dispersible with the use of food-grade surface active ingredients, such as polysorbate 80. Depending on their form, dosage and preparation method, they can give colors from yellow through orange to red. They tend to be fairly stable toward light and heat. They can be sensitive to pro-oxidative conditions, such as those found in beverages highly fortified with vitamin C or, especially, with minerals.
Anthocyanins are familiar in nature for providing vivid shades of blue, magenta, red, purple and violet. Perhaps the most common members of the anthocyanin colorant family are grape skin extract and elderberry juices, but they have been joined in recent years by red cabbage, black/purple carrots, red radishes and purple sweet potatoes. The products generally give shades of red in acidic environments, which make them ideal for beverage applications. The color shifts to blue as the pH rises, due to changes in the structure of the anthocyanin. This change is noticeable at pHs as low as 3.5 for grape skin extract and higher for others in the family.
Seeing Red
In 2007, the results of a study were released by the University of Southampton, UK, that seemed to “finally” establish a link between the consumption of synthetic food colorants and various medical conditions. As a meta-analysis of data from multiple related studies, it was interpreted to indicate that consumption of synthetic food colorants might be related to hyperactivity in children. The study has since been criticized for its methodology and for the lack of clear and direct association between synthetic colorants and hyperactivity.
Still, the “Southampton Study” captured public attention and opinion in Europe in a way that has strongly driven consumer preference away from foods colored with synthetic colorants. This, in turn, caused grocery store chains in Europe to demand food manufacturers find alternatives to synthetic food colorants. This trend, fueled largely by the “Southampton Study,” has influenced the market for food colorants in the U.S.
When Starbucks introduced its strawberry frappé beverage, which used cochineal, a bright red food colorant also called carmine, there likely was no consideration given to potential controversy. Cochineal, a red extract taken from an insect, was chosen in the formulation process because it gives an appropriate color. It also may have been a consideration that cochineal is an extremely useful, stable, naturally derived and FDA-approved food colorant.
Cochineal has a long history of use in food, cosmetics, beverages and even textiles. It does present a problem for some consumer groups because of its source. It cannot be kosher or halal, thus a problem for those who adhere to those religious dietary laws. As an animal source, it’s a problem for vegetarians and vegans. In fact, it was a member of the latter group that raised an alarm about the presence of cochineal in the Starbucks beverage. The company responded quickly with a reformulation that removed cochineal. Of course, the source of the colorant—bugs—no doubt helped create a sense of revulsion which gave the story a bigger stage.
As one of the most heat- and light-stable, natural, water-soluble red colorants, cochineal is considered hard to replace in some applications. Options usually had to be synthetic colorants. However, development of red colorants from vegetable sources has recently brought stable, vibrant reds to market. Tomato-derived reds, especially, have progressed to the point they can compete with synthetics for withstanding heat, light and pH. These new red colorants do not bleed or fade and enjoy long shelflife. Being vegetable-derived, they can satisfy makers of vegan as well as kosher and halal products.
A Little Health
Whereas synthetic food colorants offer no nutritional value at all, many of the naturally derived colorants available on the market today are derived from, or are themselves, compounds that have been shown to have some nutraceutical benefits. For instance, natural, tomato-derived reds and oranges are sources of lycopene, a carotenoid antioxidant long associated with a number of health benefits, from helping to prevent certain cancers to promoting healthy skin.
Some of the other carotenoids, such as beta-carotene, lutein and zeaxanthin, are used to add golden and orange coloring. In addition to converting beta-carotene to vitamin A, the carotenoids—especially lutein—are beneficial in helping to prevent vision loss due to retinal deterioration and cataracts. Anthocyanins, typically used for blue, purples and magenta-red colorings, also have antioxidant abilities and are believed to help reduce inflammation, DNA damage and impede tumorigenesis (tumor development).
Astaxanthin is another carotenoid only recently confirmed as GRAS for food and beverage applications as a supplement (colorants cannot, by definition, be GRAS, since they are additives, and only ingredients can be GRAS). It, too, provides a stable red color that, while previously used mostly in cosmetics and lotions that take advantage of its ability to protect the skin from UV damage, is beginning to find its way into beverages.
It should be noted that when these coloring compounds are tested, they usually perform functionally in higher concentrations. It becomes difficult to claim that the use of such a colorant creates a specific health benefit at the lower doses typically used to achieve the desired visual effect on food or beverage appearance. But, studies of the nutritional values of foods reveal there is a correlation between the health benefit associated with the foods and the total micronutrient load. With the use of biologically active colorants, they become part of that cumulative quantity and, therefore, contribute to the overall health benefit of the complete diet.
Interestingly, colorants derived from the curcuminoid compounds in turmeric (known as Natural Yellow 3), have demonstrated biological effects in amounts as low as those typically used in coloring. It can be a potent anti-inflammatory and anti-tumorigenesis substance and has been studied for possible cognitive preservation capacity. In foods, it often is used to preserve the green shades of high-acid products, such as pickles, and gets coupled with another natural gold, annatto, for coloring dairy products without bleeding. It also commonly is used (both legitimately and not) as a cheap substitute for saffron. Turmeric is sensitive to alkaline environments, however, and will shift toward red under high-pH conditions.
Shades of Brown
Caramel colorants are produced in large quantities and used throughout the food and beverage industries in a wide range of applications, but most particularly and familiarly in cola soft drinks.
Controversy arose over the presence in caramel colorings of a compound called 4-methylimidazole, referred to as “4-MEI” or “MEI.” At issue was the concern that MEIs are carcinogenic. California Proposition 65, which regulates the presence of known (to the state of California) carcinogens in food triggered a backlash against the colorant. MEIs are the result of a minor side-reaction in the process of making caramel colorants, and it appears to occur only in the particular manufacturing process that uses small amounts of ammonia salt as a catalyst.
That 4-MEI also is a chemical byproduct that occurs naturally through high-heat cooking of foods, such as coffee, meat and baked starches, gained less attention than the amounts that tested as a carcinogen. In studies to determine the carcinogenicity of 4-MEI, the amounts the animal subjects (usually mice) ate would equate to thousands of cola drinks daily for years, in human terms. Still, the concern is indicative of the sensitivity to food color sources. When the issue was raised, the industry responded very quickly with alternative production methods that eliminated the presence of MEIs in their products. As a result, the issue never became as famous as the “Southampton Study.”
Although safety does not restrict caramel colors, the fact that they are highly water-soluble usually does. For dispersible needs, as in cola beverages, that’s a plus. But for applications such as breaded coatings, visible/grill seasonings, ready meals, glazes, batters, sauces, dressings and starchy foods—such as potatoes—technologists recently developed oil-dispersible caramel colorants. These ingredients can still be labeled as “caramel coloring” but lend a stronger intensity and stable brown to foods.
A number of ingredient makers are meeting the challenge for naturally sourced and sustainable fruit, vegetable and botanical colors through advanced methods of water-extraction methods and microencapsulation for oil-soluble colors. Taking it further, some companies are focusing on the packaging of their product to ensure stability without using preservatives. Aseptic, environment-contained packaging lines and containers allow colorant processing throughout the production line and without additives.
The rapid response of color makers to burgeoning consumer awareness (and their subsequent demands) has made it easier for food and beverage makers facing reformulation challenges. Happily, they find willing and able partners with the systems and processes at the ready to meet those challenges. NS
Winston Boyd, Ph.D., is an organic chemist and color scientist. He has held a variety of positions in technology and business development. His areas of expertise include food ingredient technology, formulation technology and technical business development. Food quality and safety are major considerations in all his work, frequently including contributions in analytical methodology, as well as food quality and safety standards and programs. He can be reached at colordoc@execpc.com.
Common Plant-derived Food
Colorants and Their Actions
I. Anthocyanins
A) Sources
Red grapes
Elderberry
Red cabbage
Black/purple carrot
Purple sweet potato
Red radish
Other fruits and vegetables
B) Performance
Color
Solubility
pH stability
Heat stability
Light stability
Possible interactions
C) Applications
Acidic products
Primary color
Secondary color
Buffered shades
Color-changing products
D) Health Benefits
Bilberry–improved night vision
Elderberry–antioxidant, anti-inflammatory, antiviral, anti-mutagenic, antibacterial, anticarcinogenic, blood vessel protection, improved night vision, stress reduction, blood glucose regulation, metabolism increase, cellular oxygen consumption increase
Purple sweet potato–liver-protective effects
II. Carotenoids
A) Sources
Algae
Annatto
Carrots
Gardenia
Marigold
Palm
Paprika (Capsicum annum)
Pumpkin
Saffron
Tomato
Watermelon
B) Performance
Color
Solubility
pH stability
Heat stability
Light stability
Possible interactions
C) Applications
Oil/fat-based products
Icings, baked goods, snack foods
Dietary supplements
Water-based products
Ice cream, yogurts, etc.
Beverages
D) Health Benefits
Pro-vitamin A activity–beta-carotene and others
Antioxidant activity–lycopene, astaxanthin
Others-anti-inflammatory, antimutagenic, improved night vision, anti-carcinogenic, promotes humoral immune response, prevents age-related macular degeneration, limits sunburn damage, reduces muscle soreness
Lycopene–prostate health
Lutein, zeaxanthin–eye health
III. Betalains
A) Sources
Red Beet (Beta vulgaris)
Cactus
Pokeweed berries
B) Performance
Color
Solubility
pH stability
Heat stability
Light stability
Possible interactions
C) Applications
i. General use
ice cream, cold extruded meal bars, tablets, powdered beverages
ii. Novel applications
panned confections
iii. Advantage
non-staining
D) Health Benefits
Antioxidant activity
IV. Curcuminoids
A) Sources
Turmeric (rhizome of Curcuma longa)
B) Performance
Color
Solubility
pH stability
Heat stability
Light stability
Possible interactions
C) Applications
Pickles
Spice blends
Ice cream
Yogurt
Dietary supplements
Cauliflower
Mustard
D) Health Benefits
Antioxidant
Anti-inflammatory
Antithrombolytic
Antimutagenic
Antiviral
Antimicrobial
Antiparasitic
V. Chlorophyll
A) Sources (commercial)
Alfalfa
Nettle
Pasture grasses
B) Performance
Color
Solubility
pH stability
Heat stability
Light stability
Possible interactions
C) Applications
Dentifrices
Dietary supplements
Beverages (limited)
D) Health Benefits
Breath freshening
Strong chelating agent
Bacteriostatic
Ulcer relief
