Sergio Moser

Rapid Analysis of 27 Volatile Sulfur Compounds in Wine by Headspace Solid-Phase Microextraction Gas Chromatography Tandem Mass Spectrometry

Volatile sulfur-containing compounds (VSCs) play an important role in wine aroma conferring at high concentrations unpleasant odors but also participating positively at low concentration. A large number of VSCs are formed at different stages of winemaking and storage. To monitor this phenomenon, a HS-SPME-GC-MS/MS method has been developed. The method is proposed in order to quantify 27 different sulfur-containing compounds. SPME extraction was performed using a carboxen-polydimethylsiloxane (CAR-PDMS) fiber, which resulted the most effective fiber coating. Time and temperature extraction conditions were optimized using response surface methodology. The selectivity and sensitivity of the method were considerably increased using triple-quadrupole in multiple reaction monitoring (MRM) mode. The number of VSCs analyzed in a single run was higher than in any other method previously reported using single-quadrupole MS or other detectors. The overall process was successfully applied to identify and quantify sulfur compounds both in white and red wines.

Exploitation of simultaneous alcoholic and malolactic fermentation of Incrocio Manzoni, a traditional Italian white wine

Malolactic fermentation (MLF) is a key feature in the production of high-quality wines. Its evolution is not always guaranteed, especially in white wine, due to certain limiting factors (low pH, sulphur dioxide, low temperature) acting against malolactic bacteria. The inoculation of grape must with bacteria is an alternative approach to the management of oenological fermentation, favouring the survival of bacteria due to the absence of ethanol or sulphur dioxide – toxic compounds made by yeasts in the first stages of winemaking. We compared the activity of two strains of Oenococcus oeni during MLF in wines made from an emerging white grape variety, native to north-eastern Italy, namely Incrocio Manzoni. Different winemaking protocols were assayed, comparing sequential or simultaneous inoculation of microbial starters. The monitoring of bacterial viability through fermentations and a comprehensive characterisation of the volatile profile of the wines were achieved by advanced analytical approaches, flow cytometry and GC-MS respectively. According to the preliminary hypothesis, the chemical composition of the grape must was characterised by high acidity, which represented a serious barrier to bacterial development. Simultaneous inoculation of the two O. oeni strains ensured a regular evolution of MLF. Some differences were highlighted, both in terms of fermentation kinetics and the aromatic profile of the wines obtained, in relation to the strain of lactic bacteria. The work provides an exhaustive overview of the opportunities and risks related to different wine fermentation approaches in order to enhance the quality of white wines made from “new” or “local” wine grapes.

Induction of Terpene Biosynthesis in Berries of Microvine Transformed with VvDXS1 Alleles

Terpenoids, especially monoterpenes, are major aroma-impact compounds in grape and wine. Previous studies highlighted a key regulatory role for grapevine 1-deoxy-D-xylulose 5-phosphate synthase 1 (VvDXS1), the first enzyme of the methylerythritol phosphate pathway for isoprenoid precursor biosynthesis. Here, the parallel analysis of VvDXS1 genotype and terpene concentration in a germplasm collection demonstrated that VvDXS1 sequence has a very high predictive value for the accumulation of monoterpenes and also has an influence on sesquiterpene levels. A metabolic engineering approach was applied by expressing distinct VvDXS1 alleles in the grapevine model system “microvine” and assessing the effects on downstream pathways at transcriptional and metabolic level in different organs and fruit developmental stages. The underlying goal was to investigate two potential perturbation mechanisms, the former based on a significant over-expression of the wild-type (neutral) VvDXS1 allele and the latter on the ex-novo expression of an enzyme with increased catalytic efficiency from the mutated (muscat) VvDXS1 allele. The integration of the two VvDXS1 alleles in distinct microvine lines was found to alter the expression of several terpenoid biosynthetic genes, as assayed through an ad hoc developed TaqMan array based on cDNA libraries of four aromatic cultivars. In particular, enhanced transcription of monoterpene, sesquiterpene and carotenoid pathway genes was observed. The accumulation of monoterpenes in ripe berries was higher in the transformed microvines compared to control plants. This effect is predominantly attributed to the improved activity of the VvDXS1 enzyme coded by the muscat allele, whereas the up-regulation of VvDXS1 plays a secondary role in the increase of monoterpenes.