Blueberries – BioQuakes

Have you ever wondered how certain fruits are such vibrant colors? Scientists globally have also pondered such characteristics. Some people think that objects obtain their colors by simply having the pigment inside. However, how our eyes perceive color is much more complicated than simply seeing the pigmentation.

Recently, research has been conducted on the color of blueberries. Blueberries are considered to be a “bloom” fruit, in that it has an epicuticular wax layer and dark pigmentation. This color does not come from smushing the fruit and watching the juice emerge, which led researchers to wonder where exactly it does come from. Researchers have discovered that blueberries are covered by a thin, waxy coating that is two microns thick. The researchers discovered this by removing the waxy layer and recrystallizing it to view the particles within the layer itself.

Within this layer, there are scattered particles in a random crystalline structure that reflect blue and UV light. Photons of light have certain pigments, and only a few of which are visible to humans. The photo below depicts which light is visible to humans. It is also notable that the pigment in blueberries reflects UV light, which is visible to birds.

This directly relates to our AP Bio Photosynthesis Unit. In this unit we learned the reason why leaves are green. This is because leaves contain certain pigments (one being chlorophyll a) that absorb all wavelengths of light except for green, which is reflected.

Additionally, we learned in AP Bio that leaves are surrounded by a non-polar, waxy substance. This is the same on blueberries. It is interesting that learn that water will not easily penetrate through the skin of leaves as well as certain fruits due to the repulsion of non-polar and polar substances.

Do you know of any other epicuticular fruits? Can we investigate their pigmentation as well?

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?

BioQuakes

AP Biology class blog for discussing current research in Biology

Tag: Blueberries

Why are Blueberries Blue?

Blueberries: Why They’re Blue

Archives