For generations, scientists and food companies have been trying to replicate the taste of sugar without the health problems that accompany it. From saccharin to newer alternatives such as stevia, the goal has been to preserve sweetness while reducing empty calories, tooth decay, and the rising risks of obesity, insulin resistance, and diabetes. Researchers at Tufts University now report progress toward this goal.
In a study published in the journal Cell Reports Physical Science, the team describes a new biosynthetic method for producing tagatose, a natural but extremely rare sugar. Tagatose has a taste very similar to that of regular sugar and could offer a way to sweeten foods with fewer negative effects. The scientists also say it may come with additional health benefits.
Compared with common sugars such as glucose, fructose, and sucrose, tagatose occurs in nature only in extremely small amounts. It appears in milk and dairy products when lactose is broken down by heat or enzymes—a process that takes place during the production of foods such as yogurt, cheese, and kefir.
Small traces of tagatose are also found in fruits such as apples, pineapples, and oranges. Even so, it typically accounts for less than 0.2 percent of the sugars present in these foods. Because natural sources contain such tiny quantities, tagatose is usually produced industrially rather than extracted directly from natural raw materials.
Why producing tagatose has been difficult
“There are established processes for producing tagatose, but they are inefficient and expensive,” said Nick Neier, associate professor of chemical and biological engineering at Tufts University.
To overcome these limitations, the research team developed a new approach based on genetically modified bacteria. “We developed a way to produce tagatose by modifying the bacterium Escherichia coli so that it functions like a microscopic factory loaded with the right enzymes to convert abundant amounts of glucose into tagatose. This is far more economically viable than our previous approach, which used the less available and more expensive galactose.”
The modified bacteria were engineered to carry a recently discovered enzyme from a slime mold, known as a galactose-1-phosphate (Gal1P)–selective phosphatase. This enzyme allows the bacteria to convert glucose directly into galactose. A second enzyme produced by the bacteria, arabinose isomerase, then completes the process by converting galactose into tagatose.
Using this process, the bacteria can produce tagatose from glucose with yields of up to 95 percent. This represents a major improvement over conventional production methods, which typically achieve yields between 40 and 77 percent. The higher efficiency also makes the process significantly less expensive.
Sweetness, calories, and food safety
Tagatose provides about 92 percent of the sweetness of sucrose (table sugar) while containing roughly 60 percent fewer calories. It has been classified by the U.S. Food and Drug Administration (FDA) as “generally recognized as safe” (GRAS), meaning it can be used in foods for consumers. The same designation applies to common ingredients such as salt, vinegar, and baking soda.
One reason tagatose may be useful for people with diabetes is the way the body processes it. Only part of the sugar is absorbed in the small intestine, while a large portion is fermented by gut bacteria in the large intestine. As a result, tagatose causes much smaller increases in blood glucose and insulin levels compared with regular sugar. Clinical studies have shown very low rises in plasma glucose or insulin after the consumption of tagatose.
Tagatose may also support oral health. Unlike sucrose, which feeds bacteria that contribute to tooth decay, tagatose appears to slow the growth of some of these microbes. Research also suggests it may have prebiotic effects that support healthier bacteria in both the mouth and the gut.
Uses
Because it is low in calories and minimally absorbed by the body, tagatose works well as a “bulk sweetener.” This means it can replace sugar not only in sweetness but also in the physical structure it provides in cooking and baking. High-intensity sweeteners cannot replicate this effect. Tagatose caramelizes during cooking like regular sugar, and taste tests show that it comes closer to sugar than other sweeteners.
“The key innovation in the biosynthesis of tagatose was the discovery of the Gal1P enzyme from a slime mold and its incorporation into our production bacteria,” Neier said. “This allowed us to reverse a natural biological pathway that normally metabolizes galactose into glucose and instead produce galactose from glucose supplied as a feedstock. From there, tagatose—and potentially other rare sugars—can be synthesized.”
The researchers report that this strategy could enable more efficient production of other rare sugars as well, potentially changing how sweeteners are developed and used in the future.