Scientists have discovered a biological hack to keep French fries perfectly golden and improve their taste, potentially ending the frustration of fries turning dark and slightly bitter after frying.
Most fruits and vegetables stay better for longer when stored in a refrigerator. Potatoes, however, are better off outside, away from the cold. Exposure to low temperatures can kickstart a process called cold-induced sweetening or CIS, which is not as good as it sounds. It is an expensive problem that has been nagging the potato and snack industry for ages.
The new study published in The Plant Cell pinpointed the exact gene accountable for cold-induced sweetening and the key regulatory mechanism that switches it on when exposed to colder temperatures. Identifying the gene allowed them to rectify this issue and develop a new variety of potatoes where the trouble-making gene was silenced with the help of CRISPR editing, said Jiming Jiang, the corresponding author of this study and Michigan State University Research Foundation Professor, in an interview with Tech Times.
What causes the fries to darken? In cold storage, the VInv gene triggers a few undesirable chemical reactions within a potato. The starch in potatoes slowly breaks down into reducing sugars like glucose and fructose. These sugars, in isolation, do not make the potatoes unappetizing. However, they begin to reveal their true colors once the potatoes are subjected to high temperatures when frying or roasting.
Raw potato, like every other organism on this planet, is made up of a group of organic compounds known as amino acids. When cooked at very high temperatures, the amino acids from raw potatoes react with the reducing sugars, triggering the Maillard Reaction-the chemical reaction responsible for enhancing the flavors of cooked foods, making potatoes crispy, and giving a brown hue to bread crusts and barbecued meat.
Under typical conditions, the Maillard reaction is beneficial for bringing out flavors in potatoes. However, cold-induced sweetening pushes the reaction a bit too far due to the excess accumulation of reducing sugars in the potatoes. Thus resulting in French fries and potato chips that are darker and have a bitter aftertaste.
So, how can this be prevented?
"The expression of this gene is very minimal in the tuber during room temperature. So, if you put the tuber at room temperature on the kitchen table, it doesn't create too much sugar. But as soon as you put the potato in the refrigerator, this gene turns it on 10s or 100 times more than normal temperature, instantly creating a lot of sugars," explained Jiming.
In a household setting, the solution seems simple- Don't store potatoes in the fridge. Unfortunately, snack and fast-food manufacturers have no other way out. They need to preserve the millions of tons of potatoes in their cold storage to ensure a year-round supply of food items beyond the potato farming and cultivation season. Cold storage also ensures that the potatoes don't sprout or go bad from diseases.
Jiming said their new sweetening suppression technique is a significant step toward solving this long-standing problem in the potato industry.
CRISPR for lighter and crispier potatoes
In 2010, Jiming and his team solved the mystery of why potatoes become sweet when stored in cold conditions. They traced the cause to a gene named t vacuolar acid invertase gene or VInv and learned that wild potatoes with low expression of this gene are resistant to cold-induced sweetening effects. They demonstrated that by silencing the VInv gene, they could prevent sugar buildup in cold-stored potatoes.
In the latest study, the researchers found that the activity of the VInv gene is controlled by a specific part of its DNA called VInvIn2En. Several DNA motifs in VInvIn2En attach themselves to the transcription factors -proteins crucial to gene expression-that help potato plants respond to cold stress.
Using CRISPR, one most advanced technologies in gene editing, the researchers silenced the VInvIn2En without leaving anything behind anything extra in the potato genome," Jiming said. "Traditional methods we use to silence genes can leave behind unwanted DNA sequences elements in the potato genome, such as transgenes and antibiotic-resistant genes.The CRISPR-based methods provide a clean silencing of genes by either knocking out the gene or shutting down the mechanism of cold inducibility."
Is acrylamide in potato chips a problem?
One of the amino acids present in potatoes is asparagine, which, due to the Maillard reaction while frying, turns into acrylamide, a chemical that has been linked to being a possible carcinogen. While there has been a lot of discussion on news and social media platforms around the potential threat from this chemical in fried starchy food, 'it's not clear exactly what risk acrylamide poses to humans', states the US FDA website.
"Packaged potato snacks may not have the kind of high dose of acrylamide that rats and mice have been tested for. So, the risk is relatively lower. However, the concern is that the majority of the people in the U.S. and possibly other developing nations have some amount of acrylamide in their blood," Jagdish Khubchandani, Professor of Public Health at New Mexico State University, said in an interview with Tech Times. "Also, there are no guidelines, monitoring, or labeling of packages in most parts of the world. So, the burden is upon the consumers to limit their consumption of such foods that can expose them chronically to large amounts of acrylamide."
The researchers emphasized that the potential benefits of the new CIS-resistant potato variety extend beyond better flavor, texture, or reduced acrylamide formation. Once available commercially, these cold-resistant potatoes could offer greater flexibility in storage and transportation, potentially reducing food waste and costs.
About the author: Sanjukta Mondal is a a chemist turned science journalist. Her work has appeared in The Hindu, Biospace and other publications. Find her online at https://www.linkedin.com/in/sanjukta-mondal-181b3517b
