Production of D-Allulose from D-Fructose by Permeabilized Recombinant Corynebacterium glutamicum Cells

Allulose producers need biocatalysts that fit food-grade production. This study offers a practical answer: use permeabilized recombinant cells of Corynebacterium glutamicum to convert D-fructose into D-allulose. The host organism matters. And the numbers here are strong.

Why this matters

Most enzymatic allulose research relies on E. coli as the expression host. That works for lab work, but E. coli is not a good fit for food additive manufacturing. Regulators and customers prefer production strains with a clear safety track record. Corynebacterium glutamicum has GRAS status. It is already used in industrial amino acid production. So applying it to allulose is a natural step.

The study uses a D-allulose 3-epimerase from Flavonifractor plautii. That enzyme converts D-fructose to D-allulose. Instead of purifying the enzyme, the researchers permeabilized the recombinant cells. Permeabilized cells keep the enzyme inside, but allow substrates and products to move across the membrane. That means you skip enzyme extraction and purification. You get a whole-cell catalyst that is simpler to produce.

How the study worked

The team grew recombinant C. glutamicum expressing the epimerase. Then they treated the cells to make them permeable. They tested the permeabilized cells under different reaction conditions and settled on an optimized set. The key experiment used a very high substrate load: 750 g/L D-fructose. With just 10 g/L permeabilized cells, the reaction ran for 40 minutes.

That short reaction time is striking. Many enzymatic conversions need hours. This one was done in under an hour.

The numbers

The headline result deserves a direct look.

Parameter	Value
Substrate	750 g/L D-fructose
Catalyst	10 g/L permeabilized cells
Reaction time	40 minutes
D-Allulose produced	235 g/L
Conversion rate	31%
Volumetric productivity	353 g/L/h

A 31% conversion rate matters because allulose production from fructose is equilibrium-limited. The theoretical ceiling is around 30%, depending on conditions. So this process is running very close to what the chemistry allows. The productivity figure, 353 g/L/h, is high enough to make continuous processing attractive.

What manufacturers should consider

This work solves two problems at once. The first is regulatory. Using a GRAS host removes a major hurdle for food ingredient production. You do not want to explain to a customer why your allulose was made with an E. coli strain. C. glutamicum gives you a cleaner story.

The second is economics. Permeabilized cells are cheaper to prepare than purified enzymes. You still need to grow and treat the cells, but you skip chromatography and enzyme formulation steps. That can make a meaningful difference in cost per kilogram.

Downstream processing remains a challenge. A 31% conversion means roughly two-thirds of the fructose is still present. Separation and purification will determine whether this process is commercially viable. The paper focuses on the bioconversion step, not the full downstream train. That is normal, but ingredient buyers should remember the total cost includes much more than the reactor step.

For formulators, the main takeaway is simple: whole-cell C. glutamicum catalysts deserve serious attention. They are fast, safe, and close to equilibrium. The next questions are about scale-up stability, cell reuse, and purification compatibility.

FAQ

What does “permeabilized” mean in this context?

Permeabilized cells have treated membranes that let small molecules pass through. The enzymes stay inside the cells, so you do not need to break the cells open and purify the enzyme. It is a middle ground between free enzyme and immobilized whole-cell catalysis.

Why choose C. glutamicum instead of E. coli?

Regulatory acceptance. E. coli is common in biotech, but it is not generally considered suitable for food additive production. C. glutamicum is GRAS, which makes the path to food-grade approval much simpler.

Is 31% conversion a good result?

Yes. D-allulose production from D-fructose is limited by equilibrium, not just enzyme activity. Around 30% conversion is the expected ceiling for this reaction. Reaching 31% at 353 g/L/h productivity means the catalyst is doing its job efficiently.

The study is a clear sign that food-grade hosts can handle high-speed allulose production. For buyers and formulators, that is exactly the kind of process worth tracking.