Malic acid production from renewables: A Review

Malic acid derived from fossil resources is currently applied in the food and beverage industries with a medium global production capacity. However, in the transition from a fossil‐based to a bio‐based economy, biotechnologically produced l‐malic acid may become an important platform chemical with many new applications, especially in the field of biopolymers. In this review, currently used petrochemical production routes to dl‐malic acid are outlined and insights into possible bio‐based alternatives for microbial l‐malic acid production are provided. Besides ecological reasons, the possibility to produce enantiopure l‐malic acid by microbial fermentation is the biggest advantage over chemical synthesis. State‐of‐the‐art and open challenges concerning production host engineering, substrate choice and downstream processing are addressed. With regard to production hosts, a literature overview is given covering the leading natural production strains of Aspergillus, Ustilago and Aureobasidium, as well as Escherichia coli as the most important engineered recombinant host. The utilization of renewable substrates as an alternative to glucose is emphasized in particular as a key aspect for a competitive bio‐based production. Out of the alternative substrates discussed in this review, the industrial side‐streams crude glycerol and molasses seem to be most promising for large‐scale l‐malic acid production.