RESUMEN
We review the application of dry fermented solids (DFS) containing naturally immobilized enzymes as catalysts in synthesis and in hydrolysis reactions. The most studied application is the use of DFS containing lipases in the synthesis of biodiesel esters, by transesterification of oils or by esterification of fatty acids with short-chain alcohols in solvent-free reaction media. Other applications of DFS that have been studied include the use of DFS containing pectinases to liberate D-galacturonic acid from pectin and the production of high-value compounds by DFS containing lipases, such as the synthesis of sugar esters and the production of pure enantiomers by resolution of racemic mixtures. To date, studies are limited to proof of concept, and there are still many challenges to be faced in the development of industrial-scale processes using DFS as catalysts. A key challenge is the relatively low activity of DFS compared to commercial enzyme preparations. Attention needs to be given to scale up, not only of the bioreactor for the application of the DFS but also for the production of the fermented solids. There is also a need for economic feasibility studies to determine whether the production of DFS and their use as catalysts can be competitive at industrial scale. Graphical Abstract.