Formulating with Natural Color by Elizabeth Mannie, Cont. Ed.

Published February, 2011 Excerpts from Prepared Foods magazine (PreparedFoods.com) pp. 75,76)

Stability of Natural Colors for Beverages

Beverages are one large sector using naturally derived colors. Teas are very popular, partly due to their naturally high antioxidant content. “Now, teas are seen with added naturally derived color, such as elderberry or hibiscus extracts, adding appeal to the products,” stated Jody Renner-Nantz, food science chemist, D.D. Williamson. “Teas and other ready-to-drink beverages usually command a prime spot in the grocery store, making them more susceptible to color degradation by light,” she added.
Fruit smoothies and other refrigerated beverages often contain betalains-a group of pigments derived from beets, with magenta red hues. In contrast with anthocyanins, betalains have poor heat and light stability, which is why they are typically used only in refrigerated, dairy-type beverages, where they are protected from light.
Anthocyanins have improved heat and light stability over betalains. Ubiquitous in nature, anthocyanins are derived from fruits, vegetables, starchy legumes, grasses and flowers. Over 600 different anthocyanins have been isolated from plants. Most plants contain not just one anthocyanin, but many.
Anthocyanins have the highest stability at pH 3.0. At pH 4.5, the resonance structure of the molecule breaks, causing a dramatic decrease in color intensity, where the hue begins to change toward purple. As pH increases, the hue gets bluer. This change is reversible, however. If kept at high pH, anthocyanins begin to degrade and turn gray, such as in milk-type beverages, Renner-Nantz said.
Anthocyanins can be subdivided into two groups: acylated or non-acylated pigments. Acyl groups (phenolic or aliphatic groups) are thought to protect the flavylium cation center core of the anthocyanin molecule, by forming a sandwich structure around it through intramolecular bonding. Typical sources of acylated anthocyanins are purple carrot, purple sweet potato and red cabbage. Non-acylated anthocyanins are often derived from fruits.
The degree of acylation determines stability. For example, red cabbage and purple sweet potato anthocyanins are highly acylated and, therefore, more heat- and light-stable, while anthocyanins from fruits like elderberry are non-acylated and less stable. Interestingly, grape skin extract has both types; however, many times, grape skin anthocyanins are associated with tannins that can cause browning and precipitation during storage, especially evident at pH 3.5.
Other factors affecting anthocyanin stability include vitamin C, trace metals and minerals. Anthocyanins are recommended for use between pH 2.5-3.5. D.D. Williamson’s research shows purple carrot maintains a reddish hue over a wider pH range than other anthocyanins, making it a great choice for yogurts.
To optimize color, formulators often need to blend both fruit and vegetable anthocyanins. This is where a coloring supplier should be able to help optimize naturally derived color performance.