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Unlocking the Secret Colors in Cabbage

It turns out that you can take The Tech Interactive’s scientists out of the lab, but you can’t take the lab out of the scientists.

The team behind our BioTinkering Lab have continued to biotinker at home, and that includes coming up with a protocol to create a palette of watercolors using a single red cabbage! (You’ve got to see the video of how to do it yourself). We’ve gotten quite a few questions since we’ve shared this activity, so we asked Anja Scholze — Program Director, Biology + Design at The Tech — to peel back the layers of the science behind unlocking this veggie’s colorful secrets.

Anja Scholze, Ph.D., studied developmental biology at Stanford University before creating biotinkering experiences at The Tech Interactive.

What is the pigment in red cabbage?

Anja Scholze: The molecule that gives red cabbage its color is called flavin, which is part of the anthocyanin family. You may not know their name, but you have seen anthocyanins before — they give many berries and flowers their vibrant colors and also help create the beautiful colors of fall leaves!

What’s the importance of these natural pigments for vegetables?

AS: While biological pigments are beautiful, the color itself is often secondary — these molecules have other important biological functions in the living things that make them. For example, chlorophyll is a pigment that makes plants green but, more importantly, it is critical for photosynthesis and lets plants get energy from the sun. Anthocyanins (such as our red cabbage pigment) also do many things in plants, but two important roles are as antioxidants to help protect against stresses and colorful attractants for pollinators to support reproduction.

How is a natural pigment different from artificial dyes?

AS: A natural pigment is a colored substance that is normally produced in nature. It could be in the form of a rock or mineral or it could be made in a living thing such as a plant or insect. Humans harvest, purify, and reformulate many of these natural substances for our own purposes to use them as either pigments or dyes. Alternatively, artificial dyes are manufactured entirely in a lab setting. Sometimes the chemistry used to synthesize these molecules produces harmful waste or byproducts, but that is not always the case. The harvesting or processing of natural pigments can also be very bad for the environment (for example how blue jeans are dyed using indigo), so always do your research about the impacts of colorants in the things we use — it isn’t as simple as looking to see if they are natural or artificial!

“Cabbage Head” by Maria Robles Gonzalez. Painted entirely using watercolors created with pigments from a red cabbage.

What are some other ways people inspired by cabbage inks could explore the world of natural pigments?

AS: For anyone excited by the world of natural pigments, there is so much more to explore! Colors are all around us, and can be super fun to experiment with. For example many other foods contain pigments that can be harvested and used, such as blueberries, spinach, carrots, and beets. You could also explore working with inorganic pigments from ground up rocks and soil. Once you have colors you are interested in either as powder or a liquid, you can try things other than just making paints, such as dying fabrics or other materials and whatever else you can imagine!

Can I still eat my cabbage after taking out the pigment?

AS: Of course! The pigment molecule isn’t a substantial part of the cabbage structure, so once you have extracted what you are using for your paints, the remaining cabbage chunks are perfectly edible! And, they will be already cooked and ready for putting into a recipe of your choosing. This super fun recipe for Blaukraut (German Braised Red Cabbage) even has some insight into regional differences in German cabbage dish traditions and how that relates to natural soil pH and cabbage color!

Will these paints last?

AS: The pigment in red cabbage isn’t the most stable molecule, so some colors might fade or even change over time and with exposure to light. We have noticed that the color stability might be impacted by things such as the substrates, acids, or bases chosen and can change some as your paints dry. Additionally, because the pigment is pH sensitive, everything that the paint touches could alter the pH a bit. For example, how much water is used when painting (remember, water has a neutral pH of about 7) and the type of paper might have an impact. Making art with biology is often an exciting collaboration that you can’t control entirely. But, we like to think of that as a special bonus feature of these homemade paints — they are dynamic!

Testing two types of substrates, flour and cornstarch, that were used to make the pigments from cabbage into watercolor paints.

Is there a natural pigment for other colors of the rainbow? AS: Just look at the outside world around you, and you can see the wide variety of natural pigment colors that exist in nature! Pigments have a specific color because they absorb and reflect certain wavelengths of white light (which contains all the colors of the rainbow). Whatever color wavelengths of light are reflected is the color that our eyes see. So, while most colors are possible in nature, some are definitely more common than others. In fact, throughout history, certain, more rare natural colors, such as reds and purples have been highly prized and sought after.

How have people used natural pigments in the past? It’s clearly not a new concept, why do you think it’s so exciting to explore right now? AS: Humans have been using nature as a color palette for thousands of years. From cave paintings to modern art, natural pigments are beautiful and useful. In more recent years, scientists and companies have figured out how to manufacture some synthetic pigments using chemistry. Additionally, recent advances in biotechnology have opened the doors to using living systems to manufacture various biological pigments normally found in nature in the lab. These new ways of producing color using biology have gotten a lot of people, from scientists to artists, excited!

Have you ever had a pigment experiment go horribly wrong? AS: Haha, maybe not horribly wrong, but I have definitely had some hilarious oopses while developing cabbage inks! Mostly due to me being a very distractible scientist. The first time I was trying to make cabbage inks I didn’t pay enough attention to my boiling cabbage and definitely let the water evaporate completely! Luckily I rescued it just in time, and the pigment I washed off the bottom of the pot still produced color-changing paints — however, every color was definitely a bit more of a “burnt” shade that usual. Also, one time I set my still wet cabbage ink paints outside in the sun to dry faster, and when I came back I discovered that I had accidentally set up a lovely lunch time buffet for some local ants!! What’s the strangest smell from the BioTinkering Lab?

AS: Hmm, the most unexpected smell produced in the BioTinkeirng Lab to date is probably from our Bio Inks activity, in which we used a living bacteria to manufacture a pigment molecule that visitors could harvest and paint with. One kid claimed that the activity supplies smelled like a wet dog, other visitors were more kind in their descriptions of the odor and said it reminded them of wet earth or dirt. And, those later descriptors were exactly right! The bacteria we were using to make the pigment normally live in soil and actually produce an organic molecule called geosmin which has a distinct earthy flavor and aroma. It is responsible for the earthy taste of beets and contributes to the strong scent when rain falls on dry soil (petrichor). We had made the inside of The Tech smell like a rainy day outside just by growing some bacteria on petri dishes!

The cabbage inks activity was made possible by a Science Education Partnership Award (SEPA), Grant Number R25 GM129220, from the National Institutes of Health (NIH).

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