Ionic liquids have unique chemical properties that have fascinated scientists in many fields. The effects of adding ionic liquids to biocatalysts are many and varied. The uses of ionic liquids in biocatalysis include improved separations and phase behaviour, reduction in toxicity, and stabilization of protein structures. As the ionic liquid state of the art has progressed, concepts of what can be achieved in biocatalysis using ionic liquids have evolved and more beneficial effects have been discovered. In this review ionic liquids for whole-cell and isolated enzyme biocatalysis will be discussed with an emphasis on the latest developments, and a look to the future.

Quercetin is a flavonoid largely employed as a phytochemical remedy and a food or dietary supplement. We present here a novel biocatalytic methodology for the preparation of quercetin from plant-derived rutin, with both substrate and product being in mostly an undissolved state during biotransformation. This “solid-state” enzymatic conversion uses a crude enzyme preparation of recombinant rutinosidase from Aspergillus niger yielding quercetin, which precipitates from virtually insoluble rutin. The process is easily scalable and exhibits an extremely high space-time yield. The procedure has been shown to be robust and was successfully tested with rutin concentrations of up to 300 g/L (ca 0.5 M) at various scales. Using this procedure, pure quercetin is easily obtained by mere filtration of the reaction mixture, followed by washing and drying of the filter cake. Neither co-solvents nor toxic chemicals are used, thus the process can be considered environmentally friendly and the product of “bio-quality.” Moreover, rare disaccharide rutinose is obtained from the filtrate at a preparatory scale as a valuable side product. These results demonstrate for the first time the efficiency of the “Solid-State-Catalysis” concept, which is applicable virtually for any biotransformation involving substrates and products of low water solubility.

Aims: To examine the potential of Zymomonas mobilis entrapped into polyvinylalcohol (PVA) lens‐shaped immobilizates in batch and continuous ethanol production. Methods and Results: Cells, free or immobilized in PVA hydrogel‐based lens‐shaped immobilizates – LentiKats^®, were cultivated on glucose medium in a 1 l bioreactor. In comparison with free cell cultivation, volumetric productivity of immobilized batch culture was nine times higher (43·6 g l⁻¹ h⁻¹). The continuously operated system did not improve the efficiency (volumetric productivity of the immobilized cells 30·7 g l⁻¹ h⁻¹). Conclusions: We demonstrated Z. mobilis capability, entrapped into LentiKats^®, in the cost‐efficient batch system of ethanol production. Significance and Impact of the Study: The results reported here emphasize the potential of bacteria in combination with suitable fermentation technology in industrial scale. The innovation compared with traditional systems is characterized by excellent long‐term stability, high volumetric productivity and other technological advantages.