New Bioprocesses May Reduce Cost to Produce Low-Calorie Sweetener

Low-calorie sweeteners provide ways to satisfy sweet cravings without adding sugar and expanding waistlines. D-tagatose or tagatose, a low-calorie sweetener, is nearly as sweet as sucrose but has only 38% of the calories. In addition, the natural sweetener acts as a prebiotic to nourish beneficial gut bacteria. While tagatose has many advantages for use as a sweetener in formulated food and drink products, its cost of production has hindered its application. But that may change thanks to separate research from the University of Illinois and Tufts University on producing tagatose in a more cost-effective manner.

According to Yong-Su Jin, a professor in the department of food science and human nutrition at the University of Illinois and lead author of a study published in Nature Communications, tagatose not only tastes almost identical to sugar but also has a similar texture. Tagatose has a glycemic index of 3 while the glycemic index of sucrose is 68 and that of fructose is 24. The low-calorie sweetener therefore has a much lower risk of causing type 2 diabetes or other metabolic disorders.

Tagatose occurs naturally in dairy products and fruits but at low concentrations. Consequently, the manufacturing process to isolate tagatose involves a multi-step enzymatic process that is expensive and inefficient (only a 30% yield). Jin and his team of researchers found a means to engineer yeast cells to produce tagatose in a way that is similar to how ethanol manufacturers use yeast to produce biofuel from corn.

The bioengineered yeast directly consume lactose (an abundant sugar in dairy products) and produce a solution that is 90% tagatose. The process also indirectly utilizes whey, a by-product of the manufacturing of cheese and yogurt. Jin believes that his team’s discovery will not only lead to the increased production and use of tagatose but also a way to dispose of surplus whey in the dairy industry.

In a separate study published in Nature Communications, researchers Josef R. Bober and Nikhil U. Nair in the department of chemical and biological engineering at Tufts University describe an enzymatic bioprocess to isomerize tagatose from galactose at conversion rates up to 85%. These high rates were achieved by encapsulating L-arabinose isomerase enzyme in gram-positive Lactobacillus plantarum that was chemically permeabilized, enabling reactions at high rates, high conversions, and elevated temperatures.

According to an article published in Tufts Now, these encapsulated enzymes with permeable cell walls are mini bioreactors that allow galactose to enter the cells and convert it to tagatose, which is then released. To achieve the 85% conversion rate, the researchers had to overcome several thermodynamic, kinetic, and stability hurdles.

“You can’t beat thermodynamics. But while that’s true, you can circumvent its limitations by engineering solutions,” said Nair, who is corresponding author of the study, in the article. “This is like the fact that water will not naturally flow from lower elevation to higher elevation because thermodynamics won’t allow it. However, you can beat the system by, for example, using a siphon, which pulls the water up first before letting it out the other end.”

To optimize the reactions and achieve high conversion rates, Nair and Bober used the “siphons” of enzyme encapsulation for stability, higher temperatures to run the reactions, and feeding the bioreactors more efficiently through permeable cell membranes.