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Rewriting Life

Brewing New Fruit Flavors in Bacteria

Scientists plan to use the biofermentation of genetically engineered microorganisms to produce large batches of fruit fragrances.

Bite into a green jelly bean and your taste buds tingle with the crisp, tangy flavor of green apple or juicy pear. Now new flavors may soon make their way into your favorite candy.

Credit: istockphoto.com\matka_Wariatka

Scientists in New Zealand are developing a novel way to make flavor compounds that they think will generate more authentic tastes and aromas for candy, shampoo, and cosmetics. The process uses microorganisms engineered to express genes from fruit, which can then be brewed, like beer, to produce large amounts of flavor compounds.

Scientists in the flavor industry are constantly hunting for better ways to make tastes and smells – to find, for example, the complex combination of molecules that give an apple its unique tartness or a kiwi its special zing.

“If you use the same flavor compounds as everyone else, you get the same flavor as everyone else,” says Alan Gabelman, director of engineering sciences at Givaudan, an international flavor and fragrance company.

Jelly beans and other candy are flavored with a combination of natural and artificial ingredients. Green apple flavor, for example, might have an extract of apple skins or a combination of synthetically made alcohols and esters that mimic the flavor chemicals in an apple.

But the extraction process can be expensive, and only some chemicals can be made cheaply, limiting the complexity of resulting flavors.

In addition, scientists don’t yet know all the components of complex flavors or fragrances, which can be made up of hundreds of different compounds. Creating an authentic aroma is enormously difficult, says Chaim Frenkel, a flavor expert at Rutgers University, because scientists first must identify those compounds, then figure out how to make and combine them.

New genomics and biofermentation technologies could change that. Richard Newcomb and his team at HortResearch’s industrial biotechnology division in New Zealand have generated a database of genes involved in the taste and smell of fruits and are now using that data to engineer bacterial flavor factories. They’ve already created microorganisms that can generate the molecule responsible for the floral tartness characteristic of a green apple peel.

To make the bacteria, the researchers first isolate genes from fruit whose expression is increased at the end of the ripening process, when the fruit is most fragrant and flavorful. They then engineer that gene into a microorganism, such as bacteria or yeast, and screen the engineered microorganisms for those that produce characteristic smells, such as an apple or rose.

The screening process is largely trial and error. The bacteria are fed different chemicals to see what diet produces the best fragrance or flavor compounds. Special fibers placed in the air above the bacteria capture volatile compounds being produced by the bacteria, and the resulting compounds are analyzed using mass spectroscopy.

If a strain of bacteria produces desirable flavor or fragrance compounds, it indicates that the inserted gene is coding for an enzyme that converts a chemical precursor in the bacteria into an aromatic molecule. Isolating that enzyme gives researchers an automatic way to later synthesize large amounts of the desired molecule.

The new green apple compound, for instance, could be used in a wide array of applications – “anywhere you might want…apple flavors: shampoo, cosmetics, processed food items,” says Newcomb.

The researchers have identified 15 other genes involved in making fragrance or flavor compounds for a range of fruits, including kiwi and blueberry. They’re also working to scale up the process, so they can make industrial batches using a fermentation process similar to that used to brew beer and wine. While beer uses regular yeast for fermentation, some drugs are produced using bioengineered microorganisms similar to those being developed by HortResearch.

The technology should allow fragrance makers to produce compounds that are difficult to manufacture chemically (such as the green apple compound). It could also help scientists to identify and manufacture novel fragrance or flavor compounds, and therefore create more complex and realistic tastes and aromas. However, Rutgers’ Frenkel cautions that it will probably be difficult to engineer bacteria to create compounds that undergo a complex synthesis process.

“The approach they’re taking is kind of the wave of the future,” says Gabelman. But it could be years, he adds, before biofermentation techniques using engineered microorganisms are incorporated into the commercial flavor business.

“For something like flavors, which don’t command prices that drugs do, it’s harder to justify that technique,” he says. But as biofermentation costs drop and scientists develop the ability to make more complex arrays of compounds, Gabelman says the flavor industry will likely jump onboard.

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