Quantum Interactions: Tale of Colors in Fruits and Vegetables

Published on: May 17, 2025in

The colors of fruits and vegetables are not merely aesthetic; they signify complex quantum interactions and health benefits.

The vivid colors of fruits and vegetables arise from quantum interactions or effects in pigment molecules. Conjugated π-electron systems in pigments like beta-carotene and chlorophyll absorb specific wavelengths of visible light via electronic transitions. Moreover, using the particle-in-a-box model, we can estimate these transitions and link them to observed colors. Hence, this results from unabsorbed, complementary wavelengths.

Color Wheel (Source: thebass.org) — **Fig. 1: Color Wheel** **(Source: thebass.org)**

The year 2025 has been designated the International Year of Quantum Science and Technology (IYQ 2025). Celebrating one of the most profound and transformative fields in human knowledge. However, quantum physics, once seen as an abstract and highly mathematical domain, now forms the backbone of many modern technologies. Indeed, from lasers and semiconductors to MRI scanners and quantum computers, quantum phenomena govern some of the most fundamental natural processes. Mostly, we encounter that in everyday life.

When photons encounter matter, their energy determines whether they are absorbed or reflected. Therefore, processes are governed by quantum mechanics. Also, in the eye, photoreceptors convert these interactions into neural signals, allowing the brain to perceive color. From carotenoids in carrots to anthocyanins in berries, nature’s palette reflects the deep connection between quantum physics and human vision. Hence, a fitting tribute to the spirit of IYQ 2025. Further, this article explores how the vibrant colors of fruits and vegetables arise from quantum interactions between light and molecular pigments.

Contents

Process of Color Perception

The vivid colors of fruits and vegetables result from how their pigments absorb and reflect light. Eventually, when light strikes an object, some wavelengths are absorbed by the material, while others are reflected. However, the specific pigments in fruits and vegetables, such as chlorophyll in spinach or beta-carotene in carrots, selectively absorb certain parts of the visible spectrum. Moreover, based on their molecular structure.

Color Absorbed and Reflected (Source: pantone.com) — **Fig. 2:** **Color Absorbed and Reflected** **(Source: pantone.com)**

Therefore, the colors we perceive are those wavelengths that are not absorbed but reflected to our eyes. For example, a tomato appears red because its pigments absorb most other colors and reflect red light. Thus, the striking hues of natural produce are shaped by the selective absorption. Also, the reflection of light by plant pigments, interpreted by our visual system.

Pigments Present in Fruits and Vegetables

1. Chlorophylls–

Color: Green
Found in: Leafy Greens (Spinach, Kale, Parsley)
Types and Formulas: – Chlorophyll a: C₅₅H₇₂MgN₄O₅ and Chlorophyll b: C₅₅H₇₀MgN₄O₆

2. Carotenoids–

Colors: Orange, Red, Yellow
Found in: Carrots, Tomatoes, Corn

• Examples:

Beta-carotene: C₄₀H₅₆
Lycopene: C₄₀H₅₆
Lutein: C₄₀H₅₆O₂
Zeaxanthin: C₄₀H₅₆O₂

3. Anthocyanins–

Colors: Red, Purple, Blue
Found in: Berries, red cabbage, grapes
Example : Cyanidin-3-glucoside: C₂₁H₂₁O₁₁

4. Betalains–

Colors: Red-violet, Yellow-orange
Found in: Beets, Swiss chard, amaranth
Examples:

– Betanin: C₂₄H₂₆N₂O₁₃

– Indicaxanthin: C₁₉H₂₁N₃O₉

5. Flavonoids–

Colors: Light yellow or colorless
Found in: Apples, onions, citrus peels
Example: Quercetin: C₁₅H₁₀O₇

Complementary Colors

When a substance absorbs light of a certain wavelength, the color perceived by the human eye is its complementary color. Indeed, it is the color opposite on the color wheel.

Blue absorption (∼450 nm) appears orange
Green absorption (∼510 nm) appears magenta
Red absorption (∼650 nm) appears cyan

Quantum Physics Behind the Colour of Carrot

Carrots appear orange due to $\textit{beta-carotene}$ , which absorbs blue light. Further, we can model its electronic structure using the particle-in-a-box approximation:

$E_n = \frac{n^2 h^2}{8mL^2}$

With 22 delocalized $\pi$ -electrons (from 11 double bonds), HOMO $= n = 11$ , LUMO $= n = 12$ . Thus, the transition energy is:

$\Delta E = \frac{h^2}{8mL^2}(12^2 - 11^2) = \frac{h^2}{8mL^2}(23)$

With $L = 5.60 \times 10^{-7}~\mathrm{m}$ :

$\Delta E$ = $\frac{(6.626 \times 10^{-34})^2 \times 23}{8 \times 9.109 \times 10^{-31}}$

$\times (5.60 \times 10^{-7})^2}$

= $4.41 \times 10^{-19}~\mathrm{J}$

Hence, the wavelength is:
$\lambda = \frac{hc}{\Delta E}$

= $\frac{6.626 \times 10^{-34} \times 3.00 \times 10^8}{4.41 \times 10^{-19}}$
= $451~\mathrm{nm}$

Therefore, this matches the absorption of blue light, hence the carrot appears \textbf{orange}.

Why Carrot Juice Changes Color Over Time

The orange color of carrot juice fades over time due to the degradation of beta-carotene and other pigments. Eventually, oxidation, driven by exposure to oxygen, disrupts the conjugated double bonds in beta-carotene. Hence, forming colorless or brown degradation products. Further, ultraviolet light accelerates photodegradation, converting the more vibrant trans-isomers into less colorful cis-isomers. Moreover, heat further breaks down beta-carotene into less pigmented or colorless compounds. Additionally, enzymatic activity, particularly from polyphenol oxidase (PPO), oxidizes phenolic compounds naturally present in the juice. Thus, leading to browning and a loss of the characteristic orange hue.

Quantum Interactions- Carrot Juice Changes Color over Time — **Fig. 4: Quantum Interactions-** **Carrot Juice Changes Color over Time**

Conclusion

The vivid colors of nature — from fruits and vegetables to flowers — arise from quantum interactions within molecular pigments. Therefore, through selective light absorption by conjugated systems, quantum mechanics paints the world in complementary hues. Moreover, it reveals the invisible physics behind everyday beauty.

References

Khoo, H., Prasad, K. N., Kong, K., Jiang, Y., & Ismail, A. (2011). Carotenoids and their isomers: color pigments in fruits and vegetables. Molecules, 16(2), 1710–1738. https://doi.org/10.3390/molecules16021710
Zielinska, M., & Markowski, M. (2011). Color characteristics of carrots: Effect of drying and rehydration. International Journal of Food Properties, 15(2), 450–466. https://doi.org/10.1080/10942912.2010.489209
Blumfield, M., Mayr, H., De Vlieger, N., Abbott, K., Starck, C., Fayet-Moore, F., & Marshall, S. (2022). Should we ‘Eat a Rainbow’? An umbrella review of the health effects of colorful bioactive pigments in fruits and vegetables. Molecules, 27(13), 4061. https://doi.org/10.3390/molecules27134061

Additionally, to stay updated with the latest developments in STEM research, visit ENTECH Online. Basically, this is our digital magazine for science, technology, engineering, and mathematics. Further, at ENTECH Online, you’ll find a wealth of information.

Author
Latest Posts

Dr. Charudatta Pathak

Until 2023, Dr. Charudatta S Pathak held multiple academic positions, including lecturer, assistant professor, professor, dean, principal, director, and vice chancellor at public and private universities across India. From 2008 to 2010, he held the position of project lead in the CAE department at a European multinational corporation. Throughout his 28-year professional experience, he observed a requirement for reliable publications aimed at youngsters in grades 8 to 12, specifically for early-stage career planning. He initiated the establishment of ENTECH Digital Magazine, a complimentary periodical released on a monthly basis, accessible via stemconference.in and magzter.com. Teenagers with a keen interest in Science, Technology, Engineering, and Mathematics (STEM) and aspiring to pursue professional paths in these domains can consider reading ENTECH Digital Magazine.

Author
Latest Posts

Arvind Gupta

Arvind Gupta is a renowned Indian toy inventor, author, translator, and scientist. He was awarded “Padma Shri” by the President of India. This prestigious recognition is a testament to his exceptional contributions to the fields of innovation and [email protected]
https://arvindguptatoys.com/
https://en.wikipedia.org/wiki/Arvind_Gupta