An article published on February 7th 2024 by ScienceNews identifies and reveals why blueberries are blue. Most people reading this article are probably wondering why this is such a big deal and how it relates to science. Spoiler, it does. The secret to a blueberries hue, or color, is in the structure of its wax coat. Many fruits such as grapes, plums, and blueberries have this waxy covering and researchers have identified that it is this waxy coat that makes these fruits appear blue to humans.
Typically, blue is not a common color in nature and although there are some known blue fruits, few of them contain pigments of that shade. For example, blueberries contain large amounts of anthocyanin which is a skin pigment that should give each berry a dark red color, but structures in blueberries waxy outer layers work against anthocyanin creating their own blues.
Rox Middleton, a physicist at the University of Bristol in England and Dresden University of Technology in Germany, conducted an experiment with the help of a few colleagues to better understand what is special about the berries waxy coverings. The group looked at a variety of fruits such as blueberries, Oregon grapes, and Plums under a scanning electron microscope to take a look at the finer details of blue-colored fruit skins. The resulting images revealed nano structures that reflect blue and ultraviolet light and cover up dark red anthocyanin pigments that are found underneath the waxy coating on blueberries skin. Furthermore, wax from the Oregon grapes became transparent when it was dissolved with chloroform.
An article published on the same day through the University of Bristol provides another perspective on blueberries waxy coat. The article identifies that blueberries blue pigment can’t be extracted by squishing the berries because the pigment isn’t located in the juice that can be squeezed from the berry. The article then goes into further detail about the coating stating that it is an “ultra-thin colourant” around two microns thick that reflects UV light well which makes it appear blue as the coating is made up of miniature structures that scatter blue and UV light.
A second article published by dole, helps explains the benefits of anthocyanin. The article states that anthocyanins bind to free radicals therefore protecting against some health disorders that can arise through oxidative processes such as cardiovascular disease and cancer. The pigment is also believed to have a positive effect on inflammation and high blood pressure as well as protecting the gut from bacteria by supporting the digestive system.
To help further explain how pigments work and how we see certain colors, in AP Biology class, we learned that when a plant, for example, appears green, this is because that plant is absorbing all colors available except for green, which it reflects. This is why the rate of photosynthesis in plants is the worst in green light because the plant is unable to absorb the green light which contains the photons it requires to preform photosynthesis. Blueberries also reflect light, but it’s waxy coating instead reflects blue light which is why they appear blue to us.
I believe that these new findings are very exciting as I personally didn’t realize that a waxy coating was responsible for blueberries blue appearance. I look forward to reading about more experiments like Middleton’s that help us further understand why certain fruits and vegetables appear the way they do, what do you think?
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