Optimizing Recombinant Protein and D-Allulose Production

The process optimization was carried out by single factor optimization. Recombinant protein expression, induction time (4–20 h) and IPTG concentration (0.001–0.5 mM) were optimized stepwise following the previous descriptions (Lv et al., 2017 (link)). For cell immobilization, calcium chloride concentration (1.0%–3.0%), sodium alginate concentration (0.1%–2.0%), cell dosage (OD₆₀₀ = 10–35), and immobilization time (20–100 min) were optimized stepwise. For the D-allulose production, D-glucose concentration (20–60 g/L), reaction temperature (55–75°C), and reaction time (2–12 h) were optimized stepwise. All the bioconversions were carried out in pure water at natural pH (around 7.5). For each bioconversion, triplicated biological repeats were carried out in 250-mL shaking flasks. The statical analysis and graphing were performed using Origin Lab software (OriginLab Corporation, Northampton, MA).