Blueberries, when perfectly ripe take on a glorious deep blue-indigo color, having changed from unripe green to blue-pink. Blueberries are unique in the food world in that there are simply so very few truly blue foods out there.
So What Makes Blueberries Blue?
The skin of the blueberry is packed with biologically produced chemicals called anthocyanins. The flesh of the berry is, in fact, an ivory white color. It’s only the skin that possesses this natural dye, but when the pericarp is bruised, the anthocyanins seep into the damaged cells and color them.
The word anthocyanin comes from the Greek words anthos (meaning flower) and kyanos (meaning blue). Anthocyanins are natural pigments that run the range from dark red, to blue, to indigo, and deep violet depending on the acidity level of the pigment itself. The pH level runs the gamut in anthocyanins, the lower the pH level, the redder the pigments get, but when it increases it goes from red, to purple, to blue, to green and then yellow.
A Chemical Reaction
When mashed up or cooked, a chemical reaction takes place and the pH level increases, hence why the berries turn deep indigo or violet color as opposed to remaining in their raw, blue state.
It’s thought that this range of red to violet color is an evolutionary adaptation that plants developed as a means to attract animals. A study published in 2016 show that many insects and birds are attracted to these colors and will likely visit the plants that display them as a means of encouraging pollination via animals. As for fruit such as blueberries, cranberries, and blackberries—all rich in anthocyanins—some scientists believe that these colors attract animals that will eat the fruit that then passes the seeds on in new locations after digestion.
Anthocyanins have no flavor, but only provide a certain astringent or bitter taste to food.
There is some research published in 2015 that demonstrates their use in the elimination of free radicals from the body as antioxidants. However, other antioxidant compounds are usually found in far greater quantities in many foods knocking anthocyanins rather low on the nutritional totem pole.
Numerous Foods Possess Anthocyanins
- Red cabbage
- Blood oranges
Anthocyanins are also partially responsible for the change of color in leaves during the fall. When the weather gets colder, the leaves begin to produce high levels of anthocyanins when sap in the leaves begins to break down natural sugars. This conversion of sugar occurs due to the low levels of phosphate. This phosphate reduction happens when the tree begins absorbing phosphate from the leaves into the stems and branches as a means of protecting itself from the coming cold weather.
Reverté S, Retana J, Gómez JM, Bosch J. Pollinators show flower colour preferences but flowers with similar colours do not attract similar pollinators. Ann Bot. 2016;118(2):249-57. doi:10.1093/aob/mcw103
Nevo O, Valenta K, Razafimandimby D, Melin AD, Ayasse M, Chapman CA. Frugivores and the evolution of fruit colour. Biol Lett. 2018;14(9). doi:10.1098/rsbl.2018.0377
Nimse SB, Pal D. Free radicals, natural antioxidants, and their reaction mechanisms. RSC Adv. 2015;5:27986-28006 doi:10.1039/C4RA13315C