Production of the aroma chemicals 3-(methylthio)-1-propanol and 3-(methylthio)-propylacetate with yeasts.

Yeasts can convert amino acids to flavor alcohols following the Ehrlich pathway, a reaction sequence comprising transamination, decarboxylation, and reduction. The alcohols can be further derivatized to the acetate esters by alcohol acetyl transferase. Using L: -methionine as sole nitrogen source and at high concentration, 3-(methylthio)-1-propanol (methionol) and 3-(methylthio)-propylacetate (3-MTPA) were produced with Saccharomyces cerevisiae. Methionol and 3-MTPA acted growth inhibiting at concentrations of >5 and >2 g L(-1), respectively. With the wild type strain S. cerevisiae CEN.PK113-7D, 3.5 g L(-1) methionol and trace amounts of 3-MTPA were achieved in a bioreactor. Overexpression of the alcohol acetyl transferase gene ATF1 under the control of a TDH3 (glyceraldehyde-3-phosphate dehydrogenase) promoter together with an optimization of the glucose feeding regime led to product concentrations of 2.2 g L(-1) 3-MTPA plus 2.5 g L(-1) methionol. These are the highest concentrations reported up to now for the biocatalytic synthesis of these flavor compounds which are applied in the production of savory aroma compositions such as meat, potato, and cheese flavorings.

Biotechnological production of 2-phenylethanol.

2-Phenylethanol (2-PE) is an important flavour and fragrance compound with a rose-like odour. Most of the world's annual production of several thousand tons is synthesised by chemical means but, due to increasing demand for natural flavours, alternative production methods are being sought. Harnessing the Ehrlich pathway of yeasts by bioconversion of L-phenylalanine to 2-PE could be an option, but in situ product removal is necessary due to product inhibition. This review describes the microbial production of 2-PE, and also summarizes the chemical syntheses and the market situation.

Integrated bioprocess for enhanced production of natural flavors and fragrances by Ceratocystis moniliformis.

An integrated bioprocess (IBP) for production and recovery of de novo synthesized aroma compounds was carried out by interlinking a pervaporation membrane module with a producing bioreactor. The main aroma products of the fungus Ceratocystis moniliformis were ethyl acetate, propyl acetate, isobutyl acetate, isoamyl acetate, citronellol and geraniol. In situ product removal (ISPR) using pervaporation leads to decreased product concentrations in the bioreactor and increased microbial growth rates. As a result, by circumventing inhibiting product concentrations and thus intensifying aroma production, total yield of aroma compounds produced is higher in an IBP compared with batch cultivation. In addition, permeates obtained from pervaporation consist of highly enriched mixtures of produced flavors and fragrances.