A Bacillus-Derived D-Allulose 3-Epimerase with Rich Thermostability and Notable Catalytic Potency

You want to make allulose at scale without your enzyme dying halfway through the run. That is the whole game. This paper offers a new player that just might change your process economics.

The enzyme world for rare sugars is full of promises that break down at industrial temperatures. The study we are looking at here, published in Microbial Cell Factories (DOI: 10.1186/s12934-021-01550-1), describes a D-allulose 3-epimerase (DaeB) cloned from a plant probiotic strain called Bacillus sp. KCTC 13219. It was expressed in Bacillus subtilis cells, which matters for anyone who wants to avoid expensive expression systems.

Why should a formulator care about this specific enzyme? Because the numbers in the paper are honestly impressive.

Background: The Allulose Bottleneck

Allulose is a rare sugar with about 70% of the sweetness of sucrose and nearly zero calories. It does not spike blood glucose. That makes it attractive for keto products, reduced-sugar beverages, and bakery goods. But making it is not trivial. The standard route uses an epimerase enzyme to convert fructose into allulose. The enzyme performance dictates your yield, your purification costs, and your overall plant footprint.

The industry problem is stability. Many epimerases lose activity within hours at the temperatures needed for high substrate solubility. Fructose syrups at high concentration are viscous. You want to run hot to keep things flowing. If your enzyme cannot handle heat, you are stuck with slow reaction times or constant enzyme replacement. Both are expensive.

What the Study Did

The research team isolated a gene from Bacillus sp. KCTC 13219. They cloned it and expressed it in a food-grade Bacillus subtilis host. The resulting enzyme, DaeB, was then characterized under conditions that mimic industrial use. They tested thermal stability, catalytic speed, and conversion rates at high fructose loads.

The enzyme does not just survive. It thrives.

Key Findings

Let us get straight to the data, because the numbers speak for themselves.

The half-life of DaeB at 50°C was 25 days. Write that down. Twenty-five days. Most enzymes in this class are measured in hours or a few days at best. This is a step change in operational stability.

The catalytic rate, or kcat, was measured at 367 s⁻¹. That is not just stable; that is fast.

For conversion, they used 700 g/L fructose as the substrate. The enzyme produced approximately 200 g/L allulose. That is a conversion rate of around 28-29%, which is near the thermodynamic equilibrium for this reaction. There is no point in pushing further because the reaction will not go.

Parameter	DaeB from Bacillus sp. KCTC 13219	Typical mesophilic epimerase (reference)
Half-life at 50°C	25 days	Usually < 1-2 days
Catalytic rate (kcat)	367 s⁻¹	Variable, often lower
Allulose yield from 700 g/L fructose	~200 g/L	Often < 150 g/L
Expression host	Bacillus subtilis (food-grade)	Often E. coli

The expression host matters. E. coli can leave endotoxin contamination concerns for food applications. Bacillus subtilis is generally regarded as safe. That can simplify your regulatory pathway.

What This Means for Manufacturers

If you are producing allulose for commercial food use, this enzyme changes your reactor design options.

First, the 25-day half-life means you can run a continuous process or reuse the immobilized enzyme for multiple batches. Enzyme cost per kilogram of allulose drops significantly. Your downstream purification also gets easier because you have less spent protein to remove.

Second, the high kcat means shorter reaction times. Faster reactions mean smaller reactors for the same output. That is capital expenditure savings on tanks, piping, and facility space.

Third, the yield at 700 g/L fructose is close to the practical ceiling. The equilibrium for this reaction limits conversion. So you are not getting magic yields, but you are getting the maximum possible from your substrate. That reduces fructose recycle costs.

There is a practical note, though. The paper used 50°C as the test temperature. That is warm but not extreme. Many industrial processes run at 60°C or higher to reduce viscosity and prevent microbial contamination. You may need to verify how DaeB performs at your specific operating temperature. The half-life at higher temperatures is not provided in the abstract, so you should ask for the full data before designing a process around it.

Also, the expression was done in Bacillus subtilis. That is great for food-grade status, but you need to confirm the strain’s performance at production scale. Lab-scale expression does not always translate perfectly to a 10,000-liter fermenter.

FAQ

Is DaeB suitable for immobilization? The paper does not mention immobilization specifically. But an enzyme with a 25-day free half-life is a strong candidate for immobilization. You should test it against your preferred resin or carrier.

Do I need to remove the enzyme from the final syrup? Yes. Even with a food-grade host, the enzyme is a processing aid. You still need to remove it from the allulose syrup for clarity and regulatory compliance.

Does the enzyme require cofactors? The abstract does not mention any cofactor requirement. Most DAE-type enzymes use a simple catalytic mechanism. That means no expensive cofactor addition in your process.

Closing Thoughts

The allulose market is growing, but the economics of production are what separate winners from losers. DaeB looks like a solid piece of the cost-reduction puzzle. The stability alone justifies a closer look. Combined with the high catalytic rate and food-grade expression host, this is one of the more promising biocatalysts to come out of the rare-sugar literature in a while.

Get the full paper, run your own trials, and check the performance at your target conditions. The data in the abstract gives you every reason to test it.