Enzymatic conversions involved in the formation and degradation of aldehydes in fermented products

Abstract

The biochemical pathway leading to the formation and degradation of aldehydes, was studied with special emphasis on the identification of a branched-chain α-keto acid decarboxylase (KdcA). Using a random mutagenesis approach the gene encoding the KdcA was identified. In order to do this, a high throughput screening method was developed, based on measuring volatile metabolites by direct-inlet mass spectrometry (DI-MS). The gene of this enzyme was found to be highly homologous to the gene annotated as ipd in Lactococcus lactis IL 1403 genome, which gene product is probably inactive due to a deletion at the 3′ terminus of the ipd -gene encoding a truncated nonfunctional decarboxylase. The enzyme was further characterised using a KdcA over-expressing strain. Knowledge of the pathway of formation and degradation of aldehydes gives new opportunities in effectively improving the flavour profile of fermented food products, with a fermentation of soy milk by lactic acid bacteria as an example.