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Whole cells of Escherichia coli overexpressing a glucosyltransferase from Vitis vinifera were used for the glucosylation of geraniol to geranyl glucoside. A high cell density cultivation process for the production of whole-cell biocatalysts was developed, gaining a dry cell mass concentration of up to 67.6 ± 1.2 g L(-1) and a glucosyltransferase concentration of up to 2.7 ± 0.1 g protein L(-1) within a process time of 48 h. Whole-cell batch biotransformations in milliliter-scale stirred-tank bioreactors showed highest conversion of geraniol at pH 7.0 although the pH optimum of the purified glucosyltransferase was at pH 8.5. The biocatalytic batch process performance was improved significantly by the addition of a water-immiscible ionic liquid (N-hexylpyridinium bis(trifluoromethylsulfonyl)imid) for in situ substrate supply. The so far highest final geranyl glucoside concentration (291 ± 9 mg L(-1)) and conversion (71 ± 2 %) reported for whole-cell biotransformations of geraniol were achieved with 5 % (v/v) of the ionic liquid.

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BACKGROUND Flavor and fragrance (F&F) compounds are increasingly produced by biotechnological instead of chemical means, as this allows them to be labeled natural additives. However, since most F&F compounds exhibit cytotoxicity towards common microbiological production hosts, in situ product removal strategies using two‐phase partitioning bioreactors are desirable, making the rational selection of effective non‐aqueous phases a crucial step. Here, thermodynamic first‐principles methods and the experimental determination of partition coefficients were used to differentiate between sequestering phases with high and low thermodynamic affinity towards 17 important F&F compounds. RESULTS The approach was highly successful, enabling identification of outstanding extractants for several F&F compounds. Moreover, it was shown that certain solvent classes (e.g. long‐chained alcohols and a variety of esters) function as efficient sequestering phases across all classes of target F&F compounds, whereas other solvent types (such as alkanes), and the liquid polymer silicone oil exhibit poor partitioning behavior. Finally, the tested absorptive solid polymers generally did not constitute effective sequestering phases for the target compounds, due to high fractions of hard/crystalline segments, however, this suggests that designing polymers with a higher proportion of soft segment could lead to enhanced sorptive capacity. CONCLUSIONS This study is the first in the current literature to systematically analyze sequestering phase choices for important F&F compounds and can serve as a guide for researchers working on biphasic microbial F&F production. © 2017 Society of Chemical Industry