Production of Medium-Chain Carboxylic Acids via Chain Elongation: Challenges, Strategies, and Perspectives

Although medium-chain carboxylic acids (MCCAs) are extensively applied in food, pharmaceutical, and chemical fields, traditional approaches for their production are costly and unsustainable. Recently, the biosynthesis of MCCAs exhibits huge potential for sustainable development in both economic and environmental aspects. However, the biological method is still in its infancy and faces several challenges. A comprehensive review is therefore necessary to emphasize the recent progress in the production of biobased MCCAs. In this review, the principles of MCCA biosynthesis were introduced, and the main challenges were completely analyzed, including insufficient electron donors, byproduct accumulation, substrate competitiveness, and inhibitory factors. Moreover, several effective strategies that could improve the performance of MCCA synthesis were discussed, such as process control, biofilm, quorum sensing, electro-fermentation, bioaugmentation, and MCCA extraction. Finally, the potential of bioconversion of wasted biomass into MCCAs was analyzed toward the low-cost production of MCCAs.