From beet molasses to malic acid: holistic development of fermentation and downstream process

Area of Science:

• Biotechnology and Bioengineering
• Sustainable Chemistry

Background:

• Growing demand for sustainable alternatives to fossil-based chemicals drives interest in renewable platform chemicals like malic acid.
• Current production methods are hampered by high costs, particularly substrate costs, and challenges in downstream processing of malic acid from complex feedstocks like sugar beet molasses.
• High osmolality, inhibitors, and pigmentation in molasses fermentation complicate microbial production and separation.

Purpose of the Study:

• To develop an integrated and techno-economically feasible process for malic acid production from untreated sugar beet molasses.
• To optimize fermentative production and downstream processing for malic acid and succinic acid.
• To demonstrate the viability of using agricultural residues for sustainable platform chemical manufacturing.

Main Methods:

• Investigated fermentative malic acid production by Ustilago trichophora in various batch configurations (batch, fed-batch, pulsed batch) at shake flask and pilot scales (150 L).
• Employed membrane-based cell retention for repeated pulsed batch fermentation, achieving high titers and yields.
• Utilized activated carbon for two-stage product capture, solvent change, and decolorization, followed by crystallization for downstream purification.

Main Results:

• Produced 15.7 kg of malic acid with a titer of 108 g/L, yield of 0.50 g/g, and space-time yield of 0.66 g/L/h using repeated pulsed batch fermentation with cell retention.
• Detected byproduct succinic acid at concentrations up to 22.9 g/L.
• Developed an Aspen Plus model estimating overall process yields of 0.43 g malic acid (98% purity) and 0.10 g succinic acid per gram sucrose equivalent, with production costs competitive with market prices.

Conclusions:

• The developed holistic approach for malic acid production from untreated molasses addresses key challenges, demonstrating techno-economic feasibility at a significant scale.
• This process offers a viable route for utilizing agricultural residues as cost-effective feedstocks for platform chemical production.
• The study highlights the potential for sustainable and competitive manufacturing of organic acids from renewable resources.