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Glycosides are of commercial interest for industry in general and specifically for the pharmaceutical and food industry. Currently chemical preparation of glycosides will not meet EC food regulations, and therefore chemical preparation of glycosides is not applicable in the food industry. Thus, enzyme-catalyzed reactions are a good alternative. However, until now the low yields obtained by enzymatic methods prevent the production of glycosides on a commercial scale. Therefore, high yields should be established by a combination of optimum reaction conditions and continuous removal of the product. Unfortunately, a bioreactor for the commercial scale production of glycosides is not available. The aim of this article is to discuss the literature with respect to enzymatic production of glycosides and the design of an industrially viable bioreactor system.

The bench scale Novozym 435 ® catalysed esterification of 4-methyloctanoic acid with ethanol was studied at 35°C. Esterification in a batch reactor (molar ratio of 1:8 (acid:EtOH)) resulted in the isolation of the enantiomerically enriched product (ee p =81%) and substrate (ee s =93%). In order to integrate reaction and separation, liquid-vapour equilibria calculations were performed showing that an excess of ethanol results in a very low ester fraction in the vapour phase. Since this is undesirable for an integrated process of reaction and product removal, a repeated batch reaction was performed using a molar ratio of 10:1 (acid:EtOH). After six cycles (45% conversion) the ee of 4-methyloctanoic acid ethyl ester turned out to be 80%. For different E values the ee p was calculated for batch and repeated batch reactions. It was shown that in all cases the ee p was higher for the repeated batch reaction. However, the product is not enantiopure since the E value of the reaction is rather low at the low ethanol concentration used. An alternative approach would be the continuous separation of the product during the reaction. A mathematical model was developed to describe esterification in a packed bed reactor integrated with product separation. This model shows that integration of reaction and product removal in advance is not suitable either to obtain an enantiomerically pure product. Since the optimal reaction conditions (high ethanol concentration) and the optimal separation system (low ethanol concentration) do not match in this reaction, the preference is given to the batch reaction at high ethanol concentrations because in that case the highest enantioselectivity of the enzyme is obtained.

Branched chain fatty acids (BCFAs) are fatty acids substituted with alkyl groups. Many of them are chiral and therefore occur in two enantiomeric forms. This review describes their occurrence in Nature, their biosynthesis, their properties as flavours, and their enzymatic kinetic resolution. Many lipases are able to separate the enantiomers of BCFAs, in hydrolysis, esterification or transesterification reactions. Very often, the stereoselectivity of these reactions is remarkably high, even when the chiral carbon atom is remote from the carboxylic acid group.

Geraniol plays an important role in the fragrance and flavor industry. The corresponding glucoside has interesting properties as a “slow release” aroma compound. Therefore, the enzymatic production and downstream processing of geranyl glucoside were investigated. Geranyl glucoside was produced in a spray column reactor with an initial production rate of 0.58 mg U^-1 h^-1. A pretreated hydrophobic microfiltration membrane was used to prevent migration of the aqueous, enzyme-containing phase to the downstream process. No retention of the glucoside, which accumulated in the geraniol phase, was found. On the basis of examples from the literature, four downstream processes were tested on their viability for this system. Extraction with water and foaming were not suitable to recover geranyl glucoside from geraniol. In the first case, the glucoside selectivity for the geraniol phase was found to be high, which made extraction with water unsuccessful. In the second case it was possible to obtain a stable foam, but significant enrichment of the foam with glucoside did not occur. Adsorption on alumina and distillation under reduced pressure were applied successfully and tested in-line with the bioreactor. A maximum glucoside adsorption of 7.86 mg g^-1 was achieved on alumina. After desorption and evaporation of the extractant the pure glucoside was obtained quantitatively. A pure product could not be obtained after distillation because a small amount of glucose was present in the permeate as well, which accumulated in the bottom fraction. It was shown that with this reactor system a production of 1 kg of geranyl glucoside in 2 days is possible using an initial amount of 50,000 units of enzyme.