To anyone who has used litmus paper or owned a swimming pool, the fact that pH differences can prompt color changes should come as no surprise. But what do acidity and alkalinity have to do with color? The answer, once again, has to do with the molecular structure of pigments.
The term pH stands for "potential of hydrogen" or "power of hydrogen." You can think of pH as a logarithmic scale that describes the abundance or lack of hydrogen ions. Acidic solutions have an excess of hydrogen ions and a pH lower than 7, whereas alkaline solutions, aka bases, have an excess of hydroxide ions and a pH greater than 7.
Because of this, bases tend to yank hydrogen ions off pigments, forcing the molecules into a structural arrangement that alters their absorption patterns and, consequently, their colors. Acidic solutions, with their abundance of hydrogen ions, need no purloined electrons and weakly interact with pigments. Acid-bathed colors, unlike acid-washed jeans, tend to remain unchanged.
Our old friends the anthocyanins are prime examples of pH-controlled pigments. Most anthocyanins appear red in acidic sap but turn blue in alkaline solutions. In a neutral environment, they are violet. Thus, the same pigment that accounts for the red of roses and dahlias can provide the blue of cornflowers [source: Encyclopedia Britannica]. That's much more impressive than those color-changing T-shirts sold in the '90s.
Several patent filings for color-changing foods take advantage of pH's prodigious chromatic powers. One patent describes a "frozen dessert novelty which changes color" via pH alterations. The treat consists of two zones: One contains a low-pH substance colored with a pH-sensitive pigment, and the other contains a high-pH substance, which may or may not contain a pH-sensitive colorant. When the two parts mix through stirring, licking or swirling, the pH shift causes the color to change.
This approach provides one possible (and completely speculative) explanation for Xamaleon ice cream. It's an appealing one, because the color changes involved cover the same spectrum as anthocyanins, which scholars have nicknamed the "vegetable chameleon." Coincidence?
Linares, Xameleon's inventor, admitted to the press that the change takes place due to acids in the human mouth and temperature, which has an effect on the richness of the color of some anthocyanins. It's also possible to prepare colorless solutions containing anthocyanins and activate their color by adding the right chemicals, which could explain the necessary "love elixir" spritz [sources: Heines; Yirka].
Or not. If there's one lesson from all this, it's that chemistry provides too many color-related tricks for us to assume we've gotten the scoop on Linares' secret. But a little armchair chemistry makes for good conversation between licks of tutti-frutti.
Author's Note: How Color-changing Ice Cream Works
Researching this article rekindled my interest in color perception even more than the now infamous "is it blue or is it white?" dress on the Internet. It's a topic that everyone thinks they understand until they start researching it. But it also reawakened an interest in the rich history of pigments, a history dominated as much by happy accident as by careful chemistry, in which monopolies on particular colors could drive fortunes.
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