In this blog post, we’ll explore how humans perceive color and how the molecular structure and color of pigments change in response to pH changes, using the example of this fascinating ice cream that changes color as you lick it or as it melts.
On a peaceful Sunday afternoon, while enjoying a stroll in a quiet park under the warm sunshine, you stopped by a nearby ice cream shop and bought a sweet treat. But something’s strange. As time passes, the color of your ice cream gradually changes from what it was when you first saw it. This ice cream, which looks like something straight out of a fairy tale, is known as “Chameleon” and has sparked people’s curiosity as a color-changing treat. However, it’s difficult to say for certain that Chameleon is a product recently invented in the United States. Color-changing frozen desserts have been proposed in patents for a long time, and U.S. patents specifically describe a mechanism in which the color of the pigment changes as the pH shifts when an acidic frozen mixture is consumed alongside a mixture with a higher pH. As the saying goes, “We taste food with our eyes before it touches our tongue,” and foods that delight the eyes are gaining popularity; color-changing ice cream like “Zamelion” certainly piques people’s curiosity in this regard. So, what principle causes this mysterious ice cream to change color?
Before understanding Chameleon, we must first understand how humans perceive color. Why do peaches appear pink, and why do mangoes appear yellow? You’ve probably heard that it’s due to the pigments they contain. Pigments are molecules that selectively absorb or reflect light of specific wavelengths. So how do these molecules get perceived as specific colors by our eyes? When we look at an object, our eyes receive light that either emanates from the object itself or is reflected off its surface from another light source. The object’s surface reflects some wavelengths of light more than others while absorbing the rest, and the distribution of wavelengths in the reflected light that reaches our eyes stimulates the cone cells in the retina. The human eye contains three types of cone cells, each sensitive to different wavelengths, and the brain synthesizes the signals they send to produce the colors we see. For example, if a pigment molecule reflects a relatively large amount of light in the yellow spectrum while absorbing more light of other wavelengths, the object appears yellow to our eyes. Therefore, when our visual system processes the wavelength distribution of light reflected from a mango and entering our eyes, we perceive the mango as yellow. Of course, actual color perception is not determined solely by the process of seeing light of a single wavelength; various factors, such as color constancy depending on lighting and the surrounding environment, also come into play.
With this understanding, we can explain that the pigments in the chameleon initially reflect light of a specific wavelength predominantly, but over time, they come to reflect light of other wavelengths to a relatively greater extent. So, how does the function of these pigment molecules change? To understand this, let’s explore light absorption a little further. Light is an electromagnetic wave and possesses energy. When a molecule absorbs light, electrons within the molecule absorb the energy of the light and transition to a higher energy state. However, the energy states that electrons can occupy depend on the molecule’s structure and bonding configuration. Therefore, if the molecule’s structure changes, the wavelengths of light it absorbs may also change, and as a result, the color visible to our eyes may change as well. That said, not all objects change color over time simply because they absorb light. In most substances, even though the process of absorbing and emitting light is repeated, the molecular structure itself does not change continuously, so the visible color remains the same. When color does change, we must consider separate factors—such as light-induced chemical changes, oxidation-reduction reactions, heat-induced changes, or pH changes—that alter the molecular structure or state. In color-changing ice cream like “Zamelion,” these changes occur by altering the chemical form of the pigments. Specifically, in the method described in the patent, changes in pH alter the state of pH-sensitive pigments, which in turn changes the wavelength range of light they absorb, resulting in a color change.
While there are many types of chemical reactions, acid-base reactions and pH changes play a key role in color-changing ice cream like “Zamelion.” pH is a measure of the concentration of hydrogen ions in an aqueous solution; in acidic solutions, the concentration of hydrogen ions is relatively high, while in basic solutions, it is relatively low. In acid-base reactions, molecules exchange hydrogen ions, which can alter their molecular structure and electronic state, and consequently, their light-absorption properties may also change. In particular, anthocyanins are representative natural pigments whose color changes significantly depending on pH. Anthocyanins are found in flowers and fruits, and depending on the pH of the solution, the equilibrium between their molecular forms shifts, allowing them to display a variety of colors ranging from red to purple to blue. Therefore, using pigments that contain anthocyanins makes it relatively easy to observe the phenomenon of color changes in response to pH variations. However, the reason roses are red and cornflowers are blue cannot be explained simply by differences in pH affecting the same anthocyanin. This is because the actual color of a flower is determined by a combination of factors, including the type and molecular structure of the anthocyanins, their concentration, interactions with other pigments, and the intracellular environment and pH.
A patent related to color-changing ice cream describes a method of composing the ice cream of two distinct parts. One part contains an acidic frozen mixture and a pH-sensitive pigment, while the other contains a frozen mixture with a higher pH. As the ice cream melts or is stirred during consumption, the two parts mix, altering the overall pH; in the process, the chemical form of the pigment changes, causing the color of the ice cream to change as well. The actual patent also presents an experimental example in which anthocyanins from red cabbage extract are added to the first, acidic mixture, its pH is adjusted to approximately 3, and it is then mixed with the second mixture (pH 7), causing the color to change from red to blue-purple. In another example, an orange pigment was used to cause the color to change from orange to red during the mixing process. In other words, the key lies not in the ice cream itself magically changing color simply upon contact with saliva or air, but rather in the fact that the chemical state of the pigment changes as ingredients with different pH levels and pH-sensitive pigments mix together during consumption. Meanwhile, patents for color-changing frozen desserts also describe other methods in which layers or coatings containing different pigments mix or melt during consumption, causing the color to change; thus, not all color-changing ice creams use exactly the same principle.
In this way, we have explored the principle behind how the mysterious ice cream, “Chameleon,” changes color.
We’ve examined how the human eye perceives color and how the molecular structure of pigments and their light absorption properties change in response to pH shifts. In fact, chemical changes can affect not only color but also various other properties of molecules. For example, we can imagine foods where the substances that trigger the aromas detected by our noses undergo chemical changes, causing the scent to shift as we eat. The various sensory experiences we have with food—such as color, aroma, and taste—are influenced by the structure of the molecules in the food and the surrounding environment. If so, it’s likely that one day we’ll see an even wider variety of foods whose color, aroma, and taste all change as we eat them. If such foods become a reality, mealtimes will become much more diverse and enjoyable experiences, and food will take on an even more special meaning in our lives.
