Understanding Natural Food Colorants

Winston Boyd, Ph.D., Principal Consultant and Owner, Earthwise Technology, provided valuable insight toward a better understanding of natural food colorants in his presentation titled “Natural Colorants: The Opportunities and Challenges in Using Them Successfully,” given at Global Food Forums’ 2021 Clean Label Premium Webinar.

Boyd focused on three specific colorant classes—betalains (e.g., red beet juice), carotenoids and curcuminoids (e.g., turmeric). Time prevented a detailed discussion of additional natural colorant classes, including anthocyanins, anthraquinones and chlorophylls, among others.

Although natural colorants are very safe to use, they may not behave in predictable ways. As a product developer, it is beneficial to have a thorough understanding of their properties and functionality in a wide range of applications—from formulation through processing, storage, distribution and shelflife.

Betalains

Betalains represent the class of pigments that produce berry-like colors. Commercial preparations of betalains are generally prepared from red beets (Beta vulgaris), although they can be derived from cactus pear fruit and pokeweed berries.

The two most important coloring molecules in red beet juice are betanin and vulgaxanthin II. The later, a yellow color, is overwhelmed by the red-violet shades of betanin in beet juice. It is the conjugation of single and double bonds in these chromophores that is responsible for their respective colors, noted Boyd.

Betalains are commonly known to be susceptible to temperature abuse. In addition, the betanin structure is particularly sensitive to hydrolysis in the presence of water. “This reaction is accelerated by heat in unfavorable pH conditions,” explained Boyd, who proceeded to demonstrate the effect of pH on red beet juice in a baking application.

In a study, a simple white cake formula prepared as a muffin represented the control as the first variable. In the second variable, 1/8-tsp of baking soda and red beet juice were added to the white cake formula. In the third variable, 2 tsp of white vinegar and red beet juice were added to the formula. (See image “Impact of pH on Betalain Color.”)

Results showed that the slight alkalinity in the second variable, due to the chemical leaving agent combined with the heat of baking, destroyed the red color. By lowering the pH with vinegar in the third variable, much of the red color survived under the same baking conditions.

Based on the results of this simple study and what is known of how betalains react to adverse conditions, Boyd recommended the following solutions: control both the intensity and length of heat exposure; modify the pH of the matrix when necessary; and use betalains, such as red beet juice, in low water-activity systems, which can survive very high temperatures for extended periods of time because of the limited availability of water.

Curcuminoids

Curcumin, (derived from the word “curcuminoids”) is isolated from the rhizome of the Curcuma longa plant. The structure of the curcuminoid chromophore is responsible for the vivid yellow color for which curcumin is known. However, curcumin is quite light-sensitive and is therefore used in applications where extended light exposure can be avoided.

Boyd created a simple experiment to demonstrate the properties of curcumin. Two different oleoresin (OR) turmeric preparations were mixed in water and placed in clear glass bottles. One solution was cloudier than the other due to its formulation. The clear solution contained a more water-dispersible version of OR turmeric.

After four hours in direct sunlight at 90°F, the clear solution was nearly decolorized. The solution that was originally cloudy retained some color but lost quite of bit of its intensity and was no longer cloudy. After 12 hours in direct sunlight at 90°F, the clear solution was completely decolorized, and the other solution retained little of its original color.

This experiment showed the type of curcumin formulation can influence its stability over time. Although the cloudiness of the solution offered some protection against the harmful effect of sunlight, both solutions faded quickly, demonstrating just how sensitive curcumin is to the destructive effects of sunlight.

When using curcumin, Boyd recommended eliminating light exposure as much as possible and keeping the pH between 2.5 and 7.0. Unfortunately, no oxidative additives exist that can be used to extend the shelflife of curcumin, noted Boyd. “The best bet is physical protection from light,” he added.

Carotenoids

More commonly known sources of carotenoids include algae, annatto, carrots, marigold, palm, paprika (Capsicum annum), saffron and tomato, among others. Carotenoids can also be made via synthesis. A natural form of β-carotene, for example, can be derived from the salt-tolerant algae Dunaliella salina, from carrots and from the fungus Blakeslea trispora.

“The structure of carotenoids is characterized by a conjugated system of single and double bonds in a chain, which forms the chromophore responsible for the unique color of each molecule,” noted Boyd. Many carotenoids are oil-soluble, but some are water-soluble depending on the end groups. Water-dispersible preparations of the oil-soluble carotenoids can be made using food-grade surfactants, such as gum Arabic, he continued.

Carotenoids are susceptible to light, oxygen, pH extremes and heat. Boyd’s third experiment demonstrated these sensitivities. Oleoresin paprika (ORP), specifically 40,000 CU ORP, was spread on coarse salt; the same was repeated but with vitamin E added as a sacrificial antioxidant; and ORP was spray-dried on maltodextrin and modified food starch, thereby encapsulating it and protecting it from harsh conditions.

After nine hours in direct sunlight at 90°F, the unprotected ORP showed signs of decolorization. The ORP with vitamin E showed very little, if any degradation, which demonstrated the power of using sacrificial antioxidants to stabilize the color of carotenoids under these conditions. The encapsulated ORP showed little change.

Boyd provided the following solutions for successful use of carotenoids: control light exposure; keep the pH in the proper range; and minimize oxygen exposure by using sacrificial antioxidants.

As shown, many factors can influence the performance of natural colors. Boyd provided additional examples as follows: “pH can affect colorants’ solubility, making them unstable for use in more acidic foods and beverages; low doses of ascorbic acid in beverages (≤90ppm) can be antioxidative, while higher concentrations can be aggressively pro-oxidative; and trivalent iron (Fe³⁺) can cause rapid and dramatic degradation to color systems, causing a complete loss of color in a short time.”

Knowledge of natural colorants’ sensitivities, as well as optimal solutions for formulating with success, will help product developers produce foods and beverages that meet consumers’ expectations of quality. “Today, more than ever, consumers expect their food will be prepared with ingredients and additives they’ll understand—making natural food colorants more relevant than ever,” concluded Boyd.

Natural Colorants Q&A 

Several questions were posed to Winston Boyd at the end of the webinar regarding other natural colorant classes:

Q: Can you comment on the stability and use of purple cabbage color?
A: Red cabbage color is unique among most anthocyanins in that it is acylated causing part of its side chain to fold back over its primary structure, thereby protecting it from degradation. As such, red cabbage color would provide better shelflife than strawberry or raspberry juice. One drawback with red cabbage color is that it could have sulfury flavor notes, but most companies are adept at eliminating that problem.

Q: Are there any natural blues or greens available for confectionery applications that are stable to heat, acid and light?
A: There are two primary blue colors available in the U.S.—spirulina extract and fruit juice blend. Spirulina does not like acidic conditions; its optimal pH is in the 4-7 range. Spirulina turns gray upon exposure to too much heat; however, when the temperature is well-controlled, the pH is high enough to prevent degradation, and if it is added late in the process to minimize heat exposure, a nice blue color is possible. Spirulina can also be used in panned candy applications, but opaque packaging is necessary because of light susceptibility.

Fruit juice blends are much more stable toward pH, light and heat, but there are limits as to what natural colors will survive. In gummy candy manufacturing, for instance, natural color added toward the end of the heating process of temperatures upwards of 250°F will have good survivability for the first 30-45 minutes of the depositing process. However, if this process holds the gummy mass above 200°F for 2-3 hours, those harsh conditions will cause the color to degrade and fade over time. This means the gummies produced early in the run will be darker than the ones produced later in the run.

Understanding Natural Food Colorants, Winston Boyd, Ph.D., Principal Consultant and Owner, Earthwise Technology

Summary by Paula Frank, Online Content Manager 

To see the presentation from this event or download a pdf of the presentation, visit Using Natural Colorants Successfully [Presentation].

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