Monitoring Volatile Aroma Compounds during Fermentation in a Chemically Defined Grape Juice Medium Deficient in Leucine

Model media are frequently used to study wine fermentation outcomes, as they are considered an acceptable and reproducible representation of real juices. Identifying and quantifying the progression of the aroma compounds formed during fermentation is of importance for studies aimed at tailoring winemaking outcomes. Overexpression libraries of the yeast Saccharomyces cerevisiae can be used to determine the impact of the overexpression of specific genes. Recently, an S. cerevisiae overexpression library has been reported that encompasses a plasmid-borne construct, which utilizes a leucine-selectable marker to differentiate between yeast that contain the plasmid and those that do not. As such, these experiments with this library require a leucine-deficient fermentation medium. Aroma-progression studies have been performed in real juice and in an MS300 model medium; however, to date, none have been performed in chemically defined grape juice medium (CDGJM) or in media lacking certain amino acids. This study reports on the progression of a library of 34 enologically relevant aroma compounds formed during fermentation using a leucine-requiring wine-strain derivative of S. cerevisiae bearing the overexpression library platform plasmid and grown in a CDGJM-Leu medium. The results indicate that the production and accumulation of all 34 aroma compounds followed similar progression trends to those found in previous studies with MS300 and juice-exploiting wild-type yeast, with the exception of the compounds associated with pathways connected to the biosynthesis and metabolism of leucine. The findings confirm the likely utility of this system for evaluating the importance of overexpression of specific genes in aroma-compound production.