Genetically engineered pink pineapples are flying off shelves: What gives them their distinctive color?

Scientists have engineered a pink pineapple: It's unassuming on the outside but a blushing pink on the inside. The new "Pinkglow" pineapple, which is grown in Costa Rica, is patented and sold by food giant Del Monte and was 16 years in the making — and it's flying off the shelves.

But what gives this genetically engineered tropical fruit its rosy hue? The flesh is made pink thanks to an extra helping of lycopene, a carotenoid and pigment that occurs naturally in pineapples. It's also the compound that gives watermelon and tomatoes their reddish color.

In pineapples, lycopene is usually converted to beta-carotene by an enzyme, which makes the inside of the pineapple yellow. That enzyme, lycopene beta-cyclase, is muted in the pink pineapple, and this causes lycopene to accumulate, according to Del Monte's patent on the new fruit. Because Del Monte has claimed the pink pineapples as intellectual property,  it is the only company allowed to grow them.

According to the patent, the lycopene-converting enzyme is muted using a technique known as RNA interference. That means the company added a gene whose RNA matches and binds the RNA carrying the message to build the protein lycopene beta-cyclase, Courtney Weber, plant breeding and genetics expert at Cornell University said. Binding the RNA prevents the cell from making the enzyme. The new gene was then transferred to the pineapple genome using a type of bacteria that naturally transfers DNA to a host cell as part of its life cycle.

The genetic engineering process began in 2005, according to the patent. After six years, Del Monte tested four generations of the plant grown in Costa Rica between 2010 and 2014. The testing process for a new variety takes a long time, Weber told Live Science.

"You have to test it, put it in the field, make sure it grows right, make sure it's an acceptable variety, that it's productive enough," Weber said. And the pineapple isn't a particularly fast-growing plant.

The produce company also developed a "Honeyglow" pineapple with an extra-golden interior. In August, Del Monte reported that demand for the pink pineapples is outpacing supply and that the Honeyglow and Pinkglow together contributed to higher gross profit than in the previous quarter.

In grocery stores, the pink pineapple costs about $10, or roughly twice the price of standard varieties. And online retailers sell a single fruit for $29 to $39.

These high prices are a product of scarcity and marketing, Weber said.

"We've seen that in other varieties that were not GMO [genetically modified]," he said. For example, Honeycrisp apples and Cotton Candy grapes were both very popular and considerably higher in price than traditional varieties when they were introduced to the market. As more of these fruits are produced, the price comes down, and that will likely be the case for pink pineapples, Weber said.