Title: Bioreactor technologies for food-industry-use carboxylic acids
The C4 dicarboxylic acids succinic and fumaric acids have many uses in the food and other industries but demonstrate very different histories of commercialization. Fumaric acid was briefly manufactured by fermentation in the late 1930s and 1940s but soon fell victim to cheaper chemical processes using petrochemicals feedstocks. Succinic acid was considered a major bio-commodity chemical in phases of high oil prices in the period 1998-2013 but the collapse in oil price after 2014 rendered chemical synthesis much cheaper and “bio-succinic acid” bioprocesses collectively became the biggest failure of modern biotechnology after the demise of cloned sheep for the production of cystic fibrosis treatments.
In contrast, with no facile chemical synthesis route, D-gluconic acid bioprocesses have become major and successful examples of industrial bio-manufacturing. Unlike succinic acid or fumaric acids, D-gluconic acid biosynthesis follows a simple extra-cytosolic pathway, is purely aerobic and requires no yield-limiting redox balancing.
New reports of succinic, fumaric and D-gluconic acid fermentations using food and agricultural waste streams and non-food crops continue to appear indicating great potential for biorefinery operations. Novel bioreactors technologies have been reported for all three acids. With succinic acid, packed-bed biofilm reactors and membrane cell recycle bioreactors have reached very high volumetric productivities, out-performing conventional fed-batch fermentations. With fumaric acid, volumetric productivities have generally been low (<1 g L-1 hr-1) but the fungal Rhizopus spp. “cell factories” naturally form biofilms and rotary biofilm bioreactors have yielded productivities reaching 4 g L-1 hr-1.
A variety of fungal and bacterial species produce D-gluconic acid and several microbial producers have been used in innovative immobilized cell systems to exploit the biotransformation-like oxidation of D-glucose to D-gluconic acid. Surface matrices, which have included dual-polyelectrolytes, polyurethane sponge, calcium alginate, cellulosic microfibrils, ceramic honeycombs and microporous hollow fibers, all offer stability and productivity advantages over conventional stirred-tank bioreactors.
The economic underpinning for small- to medium-scale biorefineries1 for the production of these simple carboxylic acids is presented based on Green and Circular Economy credits for feedstock recycling in a scenario where low oil prices become the post-pandemic “new normality” as petrol- and diesel-fueled vehicles increasingly become targets for political action on a global scale and crude oil demand expectations remain depressed.
David Mousdale received his B.A. in Biochemistry from the University of Oxford, his Ph.D. degree in analytical plant biochemistry, physiology and pathology from the University of Cambridge and pursued postdoctoral research in University College Dublin and the University of Glasgow in plant cell culture, hormonal control of plant growth and development, enzymology and the molecular actions of xenobiotics. Joining the biotech spinout company Bioflux Ltd. (Glasgow) in 1988, he became Managing Director in 1997. The company name was changed in 2002 to beòcarta Ltd. (literally, “life-map”), a combination of words from Celtic languages and Latin to reflect the international nature of the company’s work with industrial biomanufacturing clients in microbial and animal cell systems for the commercial production of recombinant proteins, secondary products (antibiotics, antifungals, and enzyme inhibitors), vitamins, amino acids, enzymes, and carboxylic acids. An author of three monographs on biofuels and biorefineries, he continues to direct beòcarta’s work on the economic improvement of microbial fermentations for established products and novel metabolites, plant biomass systems, and bioenergy in Europe, the United States, Asia, and the Pacific Rim.