Blueberries are recognized globally for their distinct blue-purple skin and reputation as a source of beneficial compounds. The deep color of the exterior often leads to curiosity about what lies beneath the surface. Many people assume the vibrant hue of the skin continues throughout the fruit’s flesh. This visual difference between the deeply colored skin and the typically pale interior provides a look into the fruit’s biology and the chemical compounds that give it its signature color.
The True Interior Color
For the cultivated highbush blueberries most commonly found in grocery stores, the interior flesh is surprisingly pale, often appearing light green, whitish, or a faint yellow. This light color contrasts sharply with the deep blue of the berry’s exterior. The blue color is concentrated almost entirely within the epicarp, the thin, waxy outer layer of the fruit. The pulp contains only very low amounts of the pigment responsible for the blue color.
A key exception is the wild, or lowbush, blueberry, sometimes known as the bilberry. These varieties are often smaller and possess a dark purple or blue color consistent throughout the entire fruit. The pigment stains the flesh as intensely as the skin. While the common cultivated berry is pale inside, its wild relatives are uniformly dark.
The Role of Anthocyanin Pigments
The colors seen in blueberries, including the deep skin tone, are due to water-soluble compounds called anthocyanins. These natural pigments belong to the flavonoid group of plant compounds. Anthocyanins are responsible for a wide spectrum of colors, ranging from red and purple to blue and deep violet. The specific shade is partly determined by the acidity level (pH) within the plant cells.
In the plant, these pigments serve protective functions, such as shielding the fruit from ultraviolet (UV) light. They also play an ecological role by attracting animals for seed dispersal. The high concentration of anthocyanins in the skin provides the deep exterior color. This concentration is significant because anthocyanins are associated with the fruit’s antioxidant properties.
The interior of the common blueberry is light because anthocyanin pigments are synthesized and accumulated primarily in the epidermal cells of the skin. They are not widely distributed throughout the fruit’s pulp. The lack of these pigment molecules means the flesh remains the color of its structural components, which are naturally pale.
How Ripeness and Variety Influence Color
The interior color of a blueberry changes significantly as it matures on the bush. Unripe berries contain very little accumulated anthocyanin and have a distinct pale green color throughout. As the fruit ripens, pigments accumulate in the skin, causing the exterior to shift from green to blue. A fully ripe cultivated blueberry may occasionally exhibit a faint reddish-purple tint in its pulp, indicating pigment slightly permeating the inner tissue.
This slight color change is a marker of maximum ripeness and sugar development. The most dramatic difference in interior color remains a matter of variety. Wild lowbush blueberries have a pigment distribution that colors the flesh completely dark purple. This uniform pigment content is a genetic trait that gives them a more intense color and often a higher total level of anthocyanins compared to highbush counterparts.