Simplification of Immobilized D-Allulose 3-Epimerase Production via Pichia pastoris Secretion: A New Approach

The enzyme bottleneck in allulose production

Enzyme purification is the part of allulose production nobody likes to budget for. You grow cells, break them open, fish out the enzyme, then attach it to a support. Every step adds time and cost. A new study from Microbial Cell Factories describes a more direct route. The researchers engineered Pichia pastoris to secrete recombinant D-allulose 3-epimerase (DPEase) into the culture broth. Secretion changes the process flow. One-step purification and immobilization becomes possible, and the immobilized enzyme stays active through multiple runs.

Allulose production depends on DPEase to convert fructose into allulose. In most native systems, that enzyme stays inside the cell. Isolation means cell lysis, centrifugation, chromatography, and then immobilization. Each step creates losses. Secretion bypasses the first several steps. The enzyme leaves the cell on its own, so the broth contains the catalyst ready for immobilization.

What the study did

The team expressed recombinant DPEase in Pichia pastoris with a secretion signal. They then tested the secreted enzyme’s stability, reusability, and conversion performance. The results show a wide working range. The enzyme kept more than 80% relative activity across pH 5.0 to 11.0 and temperatures from 35°C to 70°C. Its optimum sat at pH 6.0 and 60°C. On 10% D-fructose, the maximum allulose conversion reached 17.03%.

Those numbers matter for plant design. Bioreactors often run at slightly acidic pH and elevated temperature. A catalyst that tolerates that range without extra stabilizers gives formulators more flexibility.

Key findings

Parameter	Finding
Expression host	Pichia pastoris secreting recombinant DPEase
Purification and immobilization	One-step process
pH stability	Above 80% relative activity from pH 5.0 to 11.0
Temperature stability	Above 80% relative activity from 35°C to 70°C
Optimal conditions	pH 6.0, 60°C
Reusability	83.38% relative activity after five cycles
Maximum conversion	17.03% from 10% D-fructose

The reusability figure stands out. Five cycles with 83.38% activity means one immobilized enzyme batch can handle multiple production runs. That changes the economic picture for ingredient buyers.

What this means for manufacturers

The practical message is simple: fewer steps, less handling, better reuse. Secretion removes cell disruption and most purification work. Immobilization can be coupled directly with the secreted enzyme. That cuts labor, buffer use, and equipment time.

For food formulators, the stability window is the bigger story. The enzyme operates across a broad pH range. It also handles warmer temperatures. Process designers can set conditions based on reactor efficiency, not enzyme fragility.

The 17.03% conversion is a realistic single-pass number. It is not a final product concentration. Downstream separation still does the heavy lifting. But the consistency of the catalyst matters more. A stable enzyme that survives reuse makes continuous or repeated-batch production easier to plan.

Process step	Conventional route	This secretion route
Cell lysis	Required	Not needed
Purification	Separate operation	One-step via secretion
Immobilization	Added later	Coupled to the same workflow
Enzyme reuse	Depends on support	83.38% activity after five cycles

Questions formulators ask

Is 17% conversion enough? It is a solid benchmark for a single pass. You still need separation and fructose recycling to reach commercial allulose concentrations.

What conditions should I use? Start near pH 6.0 and 60°C. The enzyme holds above 80% activity from pH 5.0 to 11.0 and from 35°C to 70°C, so you have room to adjust.

Can I reuse the immobilized enzyme? Yes. It retained 83.38% relative activity after five cycles. That suggests the catalyst can stay in service across several batches.

Secretion-based DPEase production simplifies a traditionally messy part of allulose manufacturing. The study shows a stable, reusable enzyme with a practical conversion rate. For food producers, that means fewer supply-chain bottlenecks and a clearer path to cost-effective allulose at scale.