| Summary: | To address the key issues such as low conversion efficiency of lignocellulose and unbalanced utilization of carbon sources in the biological fermentation of beet, using engineered Escherichia coli capable of simultaneously utilizing sucrose and glucose as the fermentation strains, sugar beet powder as the carbon source, combined with potassium phosphate (K<sub>3</sub>PO<sub>4</sub>) and complex cellulase treatment, staged saccharification fermentation (SHF) as the control, the efficient conversion of beet for L-lactic acid production was promoted by semi-solid synchronous saccharification fermentation (SS-SSF). The results showed that pretreatment of beet powder with K<sub>3</sub>PO<sub>4</sub> 4 g/100 ml could significantly improve the binding efficiency of substrate and enzyme. The contents of glucose and xylose in the pretreatment supernatant were the highest, which were 40.22 g/L and 4.50 g/L, respectively. Under the conditions, the lignin in beet decreased by 70% and the cellulose content increased by 53%. After secondary hydrolysis by cellulase (3 FPU/g), the total glucose yield increased by 23.88%. SS-SSF shortened the fermentation cycle by 24 h. The production and production rate of L-lactic acid were 44.51 g/L and 0.93 g/(L·h), respectively, which were 34% and 51% higher than those of staged saccharification fermentation (SHF) respectively.
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