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US researchers have developed a yeast strain that can metabolize lactose into a natural sweetener containing less than half of the calories needed for table sugar.
Yong-Su Jin, professor of food science and human nutrition at the University of Illinois, led the research team that developed the yeast strain, which produces more and more tagatose, a natural sweetener, compared to traditional enzymatic manufacturing techniques. effective alternative to sugar or high fructose corn syrup.
"Tagatose is a sweetener that has almost identical tastes and textures of sucrose or table sugar. However, tagatose contains far fewer calories than sucrose – about 40% of sucrose, "Jin said.
"In addition, it does not increase blood glucose as much as sucrose or fructose. The glycemic index of tagatose is 3, which is significantly lower than that of sucrose (68) and fructose (24).
"As such, tagatosis presents a lower risk of developing type 2 diabetes and other diseases caused by a rapid and repeated increase in blood glucose."
Despite its benefits, tagatose has a high manufacturing cost that has prevented it from being widely used in commerce, Jin added.
Although it is naturally present in fruits and dairy products, its concentrations are too low to effectively isolate tagatose. The traditional manufacturing process involves a multi-step enzymatic process that transforms galactose – a component of lactose – into tagatose.
Unfortunately, the enzyme reaction is so inefficient that only 30% of galactose is converted to tagatose, forcing manufacturers to use an expensive process to remove tagatose from the galactose mixture.
Jin's team used the internal machinery of yeast cells as tiny tagatose plants, much like ethanol manufacturers use yeast to produce fuel from corn. Researchers have developed a yeast strain producing tagatose from lactose by making two genetic modifications.
First, they released a gene that allowed yeast to use galactose as a cellular fuel during lactose metabolism. Second, they added two genes that convert galactose into tagatose.
Thus, when the yeast is fed with lactose, its own metabolism allows it to produce a solution containing 90% of tagatose, much more than the 30% yield of traditional manufacturing.
Yeast reactors also operate at much larger scales than enzyme-based ones, which could enable efficient mbad production of tagatose, Jin said.
"Another benefit is that our yeast-based process can use whey indirectly. Whey is an inevitable byproduct of Greek cheese and yogurt manufacturing processes as a raw material, "Jin said.
"Due to the recent popularity of Greek yogurt, the elimination of whey is a problem in the dairy industry.
"We hope that our process can be used to solve the problem of excess whey. Our approach based on yeast fermentation allowing higher product ratio and the direct use of inexpensive dairy waste products, we expect that the cost of production of tagatose can be significantly reduced. "
The researchers will then explore the use of their yeast-based approach to make other products from lactose.
"We have shown that lactose can be used efficiently and quickly by artificial yeast. Through further metabolic engineering, we can produce other valuable products from lactose, abundant in whey, using our artificial yeast strain, "Jin said.
The researchers published their work in the Nature Communications.
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