Green Eggs and Biochem
So the other day, I was making breakfast, right? I was scrambling some eggs, with a bit of butter and some pepper, when I thought, eh, might as well add some veggies to this, make it a bit more healthy to balance out that poutine I plan on eating later in the day. So I checked the fridge and pulled out some beautiful red cabbage that I had bought at Kensington Fruit Market (best produce near campus, highly recommended). I chopped some of it up, mixed it with my eggs, let it sauté for a bit and SUDDENLY my eggs were green. “What in the Dr. Seuss…” I thought. Being the academic weapon and incessant researcher I am, I promptly opened up Google and sent my question out into the void that is the internet. “Why did my red cabbage turn my yellow eggs green,” I asked, and within seconds the answer echoed back: anthocyanins.
Red cabbage gets its colour from a fascinating group of naturally occurring pigment molecules known as anthocyanins. These are made up of three rings of six carbons each with all sorts of fun side groups hanging off their ends. The cool part is that this complex chemistry allows a mixture of anthocyanins to react to the pH of their environment in an amazingly artistic manner. pH, for those of you who have blocked out the traumatic memory that was high school Chemistry, is the way we measure the acidity or alkalinity of a substance on a scale of 1 to 14. Anthocyanins have a variety of structures that react to light differently and thus show up as a range of colours. As the pH of a solution changes, one structure may become more stable than another and would dominate the overall colour we see.
Acidic lemon juice has a pH between 2-4, so when anthocyanins are introduced to a bit of citrus, they turn pinkish-red. Egg whites on the other hand, are one of few food items that are naturally slightly alkaline with a pH around 8-9. When met with this environment, the anthocyanins in red cabbage take on a bit of a blue-ish hue. Mix that with the yellow from the egg yolk and you get, as any primary grade art student will tell you, green!
Ranging from ruby reds to perfect pinks, pretty purples and even brilliant blues, this class of pigments is responsible for the colourful patterns on petals of flowers like red roses, hibiscus, blue cornflowers, lavender flowers, or violets. These designs help attract all sorts of pollinators to the flowers, helping the plant reproduce.
Some of the warm reds of autumn can also be attributed to anthocyanins. When the green chlorophyll is being degraded and recycled to prepare for winter, some plants fill their leaves with these anthocyanins. Here, and in many coloured fruits like grapes or blueberries, the pigment acts as a natural sunscreen protecting the plant from the harsh UV radiation in the incoming sunlight.
Anthocyanins have yet another crucial role in the plant cell, reducing oxidative stress. The plant’s proteins and biochemistry are working hard to capture and use the energy from the sun to make… more plant. In the same way that a car engine gives off excess heat and harmful side products, this cellular machinery produces ‘reactive oxygen species,’ waste molecules that move around the cell reacting with everything they bump into. Imagine a 6 year-old throwing a tantrum at the grocery store, rampaging around the shop knocking over towers of fruit and bumping into people. What do you do? You buy a lollipop and hand it to the child. That is exactly what anthocyanin does. It gives the ROS one of its electrons, returns it to a less reactive state, and sends it on its merry way. This is why antioxidants are great, and eating food rich in anthocyanins (many fresh fruits and veggies) may be really beneficial!
Looking for a way to incorporate more anthocyanins in your diet? Or hoping to wow your friends with a wondrous culinary magic trick? Perhaps you just want to relive the electric night that was the Innis Herald Speakeasy where the charming bartender made you one of his signature cocktails… what was it called… ah yes, “Eau de Sam’s Hair.” Well, you’re in luck, because for making it all the way through that heavy scientific article, you get a little reward: my not-so-secret recipe for a colour changing lemonade!
For 1 litre of lemonade you will need:
⅓ of a purple cabbage cut into thin strips
¾ cup of sugar
4-5 Lemons worth of juice
1 litre of water
And a smidgen of bartender’s flair
Bring the water to a boil, either in a kettle or on the stove. Then turn the heat off and introduce the cabbage to the water. Stir well so you can extract all those water soluble anthocyanins. Once the water has cooled completely, strain out the cabbage (collect the water). Admire the beautiful purple hue of the cabbage water then add in your sugar and stir till dissolved. You can use the leftover boiled cabbage in all sorts of dishes (omelettes, wraps, soups, fried rice, or whatever you want).
When you are ready to serve your guests, fill a fancy glass with a bit of ice, pour in the purple potion till about 3/4th the way up then add a quarter shot (about a tablespoons worth) of lemon juice. Stir gracefully and watch the drink go from purple to pink in front of your eyes as your audience erupts into oohs and ahhs. Top it off with a lemon slice and voilà! You’ve just made your first biochemistry powered magic potion.
References:
Fang, J. (2014). Bioavailability of anthocyanins. Drug Metabolism Reviews, 46(4), 508–520. https://doi.org/10.3109/03602532.2014.978080
Mattioli, R., Francioso, A., Mosca, L., & Silva, P. (2020). Anthocyanins: A Comprehensive Review of Their Chemical Properties and Health Effects on Cardiovascular and Neurodegenerative Diseases. Molecules (Basel, Switzerland), 25(17), 3809-. https://doi.org/10.3390/molecules25173809
Khoo, H. E., Azlan, A., Tang, S. T., & Lim, S. M. (2017). Anthocyanidins and anthocyanins: colored pigments as food, pharmaceutical ingredients, and the potential health benefits. Food & Nutrition Research, 61(1), 1–21. https://doi.org/10.1080/16546628.2017.1361779
Glover, B. J., & Martin, C. (2012). Anthocyanins. Current Biology, 22(5), R147–R150. https://doi.org/10.1016/j.cub.2012.01.021
Mukhopadhyay, S., Ukuku, D., Phillips, J. G., & Juneja, V. K. (2012). Survival and growth of Salmonella enterica serovar enteritidis in membrane-processed liquid egg white with pH, temperature, and storage conditions as controlling factors. Journal of food protection, 75(7), 1219–1226. https://doi.org/10.4315/0362-028X.JFP-11-436
Gould, Kevin., Davies, K. M., & Winefield, Chris. (Eds.). (2009). Anthocyanins biosynthesis, functions, and applications (1st ed. 2009.). Springer New York. https://doi.org/10.1007/978-0-387-77335-3
Khoo, H. E., Azlan, A., Tang, S. T., & Lim, S. M. (2017). Anthocyanidins and anthocyanins: colored pigments as food, pharmaceutical ingredients, and the potential health benefits. Food & Nutrition Research, 61(1), 1–21. https://doi.org/10.1080/16546628.2017.1361779
Cserhalmi, Z., Sass-Kiss, Á., Tóth-Markus, M., & Lechner, N. (2006). Study of pulsed electric field treated citrus juices. Innovative Food Science & Emerging Technologies, 7(1), 49–54. https://doi.org/10.1016/j.ifset.2005.07.001