Production, Purification, Characterization, and Safety Evaluation of Constructed Recombinant D-Psicose (Allulose)

Why allulose buyers should care

Allulose buyers keep asking one question: can enzyme technology make this sugar affordable at scale? A new paper in Microbial Cell Factories (DOI: 10.1186/s12934-024-02487-x) moves that answer forward. The team built a recombinant D-psicose 3-epimerase, expressed it in E. coli, and ran a safety screen on the finished syrup.

The background: allulose needs enzymes

D-psicose is the chemical name for allulose. It delivers bulk and sweetness without the calories of sucrose. The problem is manufacturing. No crop yields it in commercial quantities. So producers turn to biocatalysis: enzymes that rearrange fructose into allulose.

The workhorse enzyme is D-psicose 3-epimerase, or DPEase. It flips the C-3 hydroxyl group of fructose, converting the molecule into allulose. The reaction hits equilibrium well before full conversion. So every extra percentage point of conversion matters.

What the study did

The researchers constructed a recombinant DPEase and expressed it in E. coli. They optimized the purification process and the reaction conditions. Then they tested the enzyme against a 25% fructose solution. Finally, they ran an acute toxicity study in rats using the actual D-fructose-D-allulose mixed syrup the process generates.

Key findings

Purification optimization delivered a big jump. The specific activity of the purified enzyme increased 21.03 times over the baseline.

The reaction conditions were practical for industrial adoption. At pH 7.5 and 55°C, with 10 mM Mn²⁺, the allulose concentration reached 5.60%. That translates to a 22.42% conversion rate from fructose.

The safety results were equally important. The acute toxicity study showed no adverse effects in rats, supporting the syrup's safety profile.

Parameter	Study condition	Formulator consideration
Substrate	25% fructose	Higher solids mean less water to remove downstream
Temperature	55°C	Compatible with standard process tanks
pH	7.5	No acid-resistant alloys required
Metal cofactor	10 mM Mn²⁺	Manganese must be tracked in the final food-grade syrup
Conversion	22.42%	Residual fructose stays high; expect a mixed syrup

What it means for manufacturers

A 22.42% conversion rate is a solid benchmark. If you are evaluating allulose suppliers, ask what conversion rate their enzyme actually achieves. Anything near 22% is respectable.

The 55°C working temperature fits most existing enzymatic processes. That lowers retrofit costs. You won't need new heating or cooling infrastructure.

Manganese deserves attention. The reaction depends on it. In a food product, that metal ion must be controlled. Ask whether the supplier removes it or declares it on the label.

The toxicity data is a green flag. Acute safety results on the mixed syrup support regulatory progress. Keep in mind this is acute data only. Chronic studies may still be required for novel food approval in some regions.

FAQ

Is D-psicose the same as allulose? Yes. D-psicose is the chemical name. Allulose is the commercial name. They are identical molecules.

Why does conversion rate affect my formulation? A lower conversion rate leaves more fructose in the syrup. Fructose is sweeter and calorie-bearing. That shifts both the sweetness profile and the nutrition panel of your end product.

How much fructose actually converted here? Starting from a 25% fructose solution, the optimized enzyme produced 5.60% allulose, a 22.42% conversion. The remaining liquid is mostly fructose alongside the allulose.

Where this leaves formulators

The paper offers a clear snapshot of what modern DPEase technology can deliver. The enzyme works at reasonable temperatures, hits a solid conversion rate, and the syrup passed an acute safety screen. The next questions belong at production scale: how does the enzyme hold up in thousands of liters, and what does manganese removal cost per kilogram? Watch for those answers.