5. Conclusion
Herein, we successfully created the NADP+-dependentPd PDHD36A/I37R and constructed the NADPH
recycling module. By employing the constructed GS-linker system in
vitro to assemble the oxidoreductases, the D-tagatose
yield from lactose (0.378 g/g) was 9.28-fold higher than the initial
yield. Furthermore, whey, a by-product in cheese production, was used as
the sole material for producing D-tagatose, bioethanol,
and microbial protein with an integrated bioprocess combined with
enzyme cascade and anaerobic
fermentation. Finally, 266.5 gD-tagatose, 371.3 g bioethanol, and 215.5 g dry yeast
(including 38% protein) were obtained from 1 kg WP (including 810 g
lactose). The economic feasibility was improved owing to the expensive
price of D-tagatose, compared with those of bioethanol
and microbial protein. Moreover, the risk of food safety was avoided
owing to non-GMO technology. This bioprocess in which the dairy waste
was entirely utilized helps reduce the net emission of carbon dioxide
and drives sustainable development.
Acknowledgements
The authors would like to thank Dr. Sen Wang from State Key Laboratory
of Microbial Technology of Shandong University for help and guidance in
transmission electron microscopy. This work was supported by National
Key R&D Program of China (No. 2018YFA0901700), National Natural Science
Foundation of China (No. 32271526).