Erythritol is a naturally abundant sweetener gaining more and more importance especially within the food industry. It is widely used as sweetener in calorie-reduced food, candies, or bakery products. In research focusing on sugar alternatives, erythritol is a key issue due to its, compared to other polyols, challenging production. It cannot be chemically synthesized in a commercially worthwhile way resulting in a switch to biotechnological production. In this area, research efforts have been made to improve concentration, productivity, and yield. This mini review will give an overview on the attempts to improve erythritol production as well as their development over time.
Over time, different approaches have been applied to increase the production of erythritol. Because the demand of erythritol increased in a short time, the commercial availability became most important. First priority was a fast optimization of the fermentation parameters for the cultivation of known erythritol-producing organisms and random mutagenesis. Although the enzymes were soon known, and in some cases have already been characterized, just little research focused on the regulation of the expression of the corresponding genes. Only in the last few years, hypotheses about gene regulation started to be enlightened by targeted gene editing. The knowledge achieved from this research turned out to be useful for targeted genetic strain improvements and opened up new parameters for further fermentation optimization. Later on, the question about ecological sustainability arose. Is it justifiable to produce a sugar substitute using a sugar as feedstock, thereby creating a product that is furthermore expensive? The research work performed on the industrial cellulase and hemicellulase production strain T. reesei tried to combine all different optimization approaches. The organism is able to degrade lignocellulosic material and can therefore utilize renewable and cheap material, like wheat straw as starting material. The substrate can be pretreated to facilitate analysis and speeding up the degradation by T. reesei. The key enzyme for the synthesis of erythritol is naturally present in T. reesei and has been successfully expressed and characterized in Escherichia coli. Finally, leads an overexpression of this gene to an increase in erythritol synthesis. The ongoing research focuses on getting a whole picture about the pathway of erythritol synthesis, the enzymes involved, and the influence of certain production parameters like osmotic pressure with the aim to gain a value-added product from cheap renewable biomaterial.