Ava Fasciano / Sun Graphic Designer

December 2, 2020

The Science Behind Pumpkin Coloration

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Plant Science Professors Li Li and Micheal Mazourek weigh in on the science behind fall’s colorful pumpkins. 

From jack-o’-lanterns to pumpkin spiced lattes to pumpkin pie, there is no doubt that a majority of Americans enjoy eating and carving these traditionally orange pumpkins, especially in the fall.

According to Prof. Michael Mazourek, plant science, pumpkins are orange because of carotenoids — the same compounds that synthesize to become vitamin A and give carrots their orange hue as they grow.

In trees, when chlorophylls degrade, carotenoids are leftover in tree leaves, which gives them a yellowish color in the fall. However, the coloration process is slightly different in vegetables like pumpkins, according to Prof. Li Li, plant science.

“As pumpkins mature, they continuously synthesize carotenoids which give them their signature orange color,” she said. 

Li said various plants produce approximately 50 or 60 different types of carotenoids commonly found in foods, but over 1,000 different varieties of carotenoids exist in nature, including in fungi, bacteria and even some insects.

Beyond pumpkins, many other fruits and vegetables like cantaloupes, sweet potatoes and carrots also synthesize and accumulate carotenoids, Li said.

According to Mazourek, there are at least three pumpkin species: Cucurbita pepo, Cucurbita moschata, and Cucurbita maxima. Cucurbita pepo is most commonly seen around Halloween, as these are the pumpkins people use to carve jack-o’-lanterns.

Cucurbita moschata can be found in cans of pumpkin pie filling and are the types of pumpkins that “look like Cinderella’s coach,” according to Mazourek.

The last species, Cucurbita maxima, can grow to weigh 2,000 pounds and is typically used to make the tempura squash found in bento boxes, Mazourek said.

 “It is very common to have pumpkins that are not fully ripened in the field and have patches of green remaining, warts, or patterns of color,” Mazourek said. Typically, these are left in pumpkin fields to compost.  

While pumpkins are typically orange, pumpkins can actually be many different colors. Mazourek said there are additional pumpkin species that can be blue, gray, and pink. But Li added that in general, most pumpkins maintain their yellow-orange color and blue, gray, and pink pumpkins are much rarer.

Beyond aesthetics, pumpkin discoloration can also affect its flavor. “If the pumpkin is still greenish and less ripe, it will taste similar to a green banana,” Mazourek said.

Mazourek also said it is important to check for rotty spots or mold on a pumpkin, or “areas that look like you spilled water on a paper bag,” as these factors can also negatively impact the pumpkin’s taste.