L-Malic acid is a dicarboxylic acid found in all living organisms, with its name derived from its initial isolation from unripe apples in 1785. It has been classified as a safe food-grade product by the US Food and Drug Administration (FDA) and is primarily used as an acidulant and flavor enhancer in the food and beverage industries. The demand for malic acid is growing, driven by its improved taste retention and more intense acid taste compared to citric acid. The current global malic acid production capacity is estimated to be between 80,000 and 100,000 tons per year, while the annual market demand is over 200,000 tons.
This review focuses on the latest progress in malic acid production, biosynthetic pathways, and metabolic engineering strategies. It covers the production of malic acid using wild-type microorganisms, including filamentous fungi, yeasts, and bacteria. The review also discusses the use of enzyme-based bioprocesses for the production of malic acid, as well as the metabolic engineering of microorganisms for improved production. Overall, the use of microorganisms as cell factories for industrial production of malic acid is a promising field with great potential for further development.