Abstract
Less than 1 % of the annual worldwide consumption of vanillin can be met by extracting the aromatic compound from vanilla (Vanilla planifolia) pods. For 150 years, vanillin has also been derived through chemical synthesis, which remains the main source (>80 %) of vanillin today, despite growing environmental concerns due to considerable chemical waste disposal issues. 'Natural' vanillin is in high demand for flavour and fragrance applications. Thus, biotechnological routes using an array of recombinant hosts have been devised to obtain vanillin through fermentation of natural precursors, e.g. ferulic acid, (iso)eugenol and glucose. These processes, often classical biotransformations, result in 'natural' vanillin according to European and US legislation. A significant technical hurdle in fully fermentative routes is vanillin toxicity, which impairs cellular proliferation at relatively low, i.e. commercially uninteresting, vanillin concentrations. In addition to adopting the plant-derived solution, i.e. product glycosylation, to sequester and store vanillin glycosides, sophisticated in situ product removal strategies have been used to obtain industrially relevant amounts of 'natural' vanillin.