A Review on the Production of C4 Platform Chemicals from Biochemical Conversion of Sugar Crop Processing Products and By-Products

Abstract

The development and commercialization of sustainable chemicals from agricultural products and by-products is necessary for a circular economy built on renewable natural resources. Among the largest contributors to the final cost of a biomass conversion product is the cost of the initial biomass feedstock, representing a significant challenge in effective biomass utilization. Another major challenge is in identifying the correct products for development, which must be able to satisfy the need for both low-cost, drop-in fossil fuel replacements and novel, high-value fine chemicals (and/or commodity chemicals). Both challenges can be met by utilizing wastes or by-products from biomass processing, which have very limited starting cost, to yield platform chemicals. Specifically, sugar crop processing (e.g., sugarcane, sugar beet) is a mature industry that produces high volumes of by-products with significant potential for valorization. This review focuses specifically on the production of acetoin (3-hydroxybutanone), 2,3-butanediol, and C4 dicarboxylic (succinic, malic, and fumaric) acids with emphasis on biochemical conversion and targeted upgrading of sugar crop products/by-products. These C4 compounds are easily derived from fermentations and can be converted into many different final products, including food, fragrance, and cosmetic additives, as well as sustainable biofuels and other chemicals. State-of-the-art literature pertaining to optimization strategies for microbial conversion of sugar crop byproducts to C4 chemicals (e.g., bagasse, molasses) is reviewed, along with potential routes for upgrading and valorization. Directions and opportunities for future research and industrial biotechnology development are discussed.