Researchers use yeast to manufacture low-calorie sweetener

University of Illinois researchers have used a yeast-based approach to produce tagatose, a natural, low-calorie sweetener, which may help increase its commercial use.

The researchers, led by Yong-Su Jin, Professor of Food Science and Human Nutrition, developed a strain of yeast that can metabolise lactose into tagatose in much larger quantities than traditional enzymatic manufacturing techniques. This means it could be a cheaper alternative to sugar.

"Tagatose is a sweetener that exhibits almost identical tastes and textures of sucrose, or table sugar. However, tagatose has many fewer calories than sucrose — about 40% of sucrose," explained Jin. "In addition, it does not increase blood glucose levels as much as sucrose or fructose. The glycaemic index of tagatose is 3, which is much lower than that of sucrose, 68, and fructose, 24. As such, tagatose carries a lower risk for developing Type 2 diabetes and other diseases caused by rapid and repeating glucose increases in blood."

However, he said high manufacturing costs have hindered its commercial use. Although it is naturally present in fruits and dairy products, the concentrations are too low to isolate tagatose effectively.

Traditionally, a multi-step enzymatic process is used to turn galactose — a component of lactose — into tagatose, but this manufacturing method is highly inefficient. Only 30% of galactose is converted into tagatose, forcing manufacturers to use an expensive process to remove the tagatose from the galactose mixture.

Jin's team managed to increase this yield to 90% using a yeast-based process. They engineered a strain of yeast that produces tagatose from lactose by making two genetic tweaks: they took out a gene that let the yeast use galactose as cellular fuel during lactose metabolism, and added two genes that convert galactose into tagatose.

Thus, when the yeast is fed lactose, its own metabolism drives it to produce a solution that is 90% tagatose. Yeast reactors also operate on much larger scales than enzyme-based ones, which could allow for efficient mass production of the sweetener, according to Jin.

He said the yeast-based process uses whey indirectly, which offers cheese and Greek yoghurt manufacturers a way to dispose of the by-product.

"We hope our process can be used to resolve the surplus whey problem. As our yeast fermentation-based approach allows a higher product ratio and the direct use of inexpensive dairy waste, we expect that the production cost of tagatose can be significantly reduced."

The team plan to use their yeast-based approach to manufacture other products from lactose.

The research was published in the journal Nature Communications.

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