One of the biggest hurdles in finding a healthy, affordable alternative to table sugar or sucrose is the ability to make it. One such alternative is allulose, which is about 70% as sweet as sucrose but has only 10% of the calories, and has even been shown to improve blood sugar levels and aid weight loss in people with type 2 diabetes. However, current production methods are known for low yields and poor quality, which has hindered its development.
Now, scientists at the University of California, Davis (UCDavis) have made a "major breakthrough" in the production of allulose, using a method that both delivers high-quality yields and is feasible and scalable, making it a viable, healthier sugar alternative. This method also rewrites the current way of sourcing cellulose and can quickly promote its commercial production.
"Cellulose is a great sugar substitute, but we don't yet have a cost-effective way to produce it," said Shota Atsumi, a professor of chemistry at the University of California, Davis. "Our new method is efficient, cost-effective, and can be scaled up for commercial production."
Allulose (also known as D-brown rice sugar) is considered a rare sugar because it occurs naturally in trace amounts in only a few plant foods, such as wheat, figs, and raisins. Once extracted, it has the texture and taste of sucrose with only 0.4 calories per gram, compared to 4 calories per gram of sucrose. Since it is a monosaccharide, a single sugar molecule, it goes through a very different process in the human body. Approximately 70% is absorbed by the small intestine and excreted in the urine within 24 hours. The rest is excreted through the scenic route of the large intestine in about 48 hours. Therefore, allulose does not affect blood sugar or insulin levels.
Currently, the enzymes D-tagatose-3-epimerase (DTEase) (DTEase) and D-psicose-3-epimerase (DPEase) are used to extract psicose and catalyze its conversion from fructose, but the limitations of this process mean that the yield can only reach 50% at most, and the purity is very low.
Instead of trying to increase the production of these enzymes, scientists at UC Davis turned to finding another way to produce the sugar entirely. They found this method in the common gut bacterium Escherichia coli (E. coli).
The team, working with the Mars Advanced Research Institute, edited the microbes' metabolic processes so that when the cells were fed glucose, they converted it into psicose. As a result, the yield immediately reached 62% (and importantly, the purity exceeded 95%).
"Once the flux is redirected, you find that the cells have everything they need; they just need to be turned on, and pathways that are not needed are turned off," Atsumi said.
Basically, E. coli naturally has the right pathway to produce aurinose from glucose, and the scientists tweaked the design to flip the switch to a specific metabolic outcome. Not only does this new method produce psicose, it is also sustainable and cost-effective, allowing production to be scaled up using existing infrastructure and biochemical technologies.
"Whole-cell catalysis technology and infrastructure are already established industrially and can provide the model organism E. coli with feedstocks that do not compete with commercial food production," the researchers noted in the paper. "The ability to batch produce rare sugars will provide low-calorie sugar alternatives to ultra-processed foods, thereby helping to address rising obesity rates worldwide. Increased production of rare sugars will also provide sustainable pesticides to the agricultural industry and simple sugars with medicinal value to the pharmaceutical industry."
And, because the modified E. coli devour all the glucose fed to them, little downstream work is needed to improve purity, which solves another hassle with current production methods.
The research was published in the journal Nature's Science of Food.