Abstract
To allow for a broad survey of subtle metabolic shifts in wine caused by rootstock and irrigation, an integrated metabolomics-based workflow followed by quantitation was developed. This workflow was particularly useful when applied to a poorly studied red grape variety cv. Chambourcin. Allowing volatile metabolites that otherwise may have been missed with a targeted analysis to be included, this approach allowed deeper modeling of treatment differences which then could be used to identify important compounds. Wines produced on a per vine basis, over two years, were analyzed using SPME-GC-MS/MS. From the 382 and 221 features that differed significantly among rootstocks in 2017 and 2018, respectively, we tentatively identified 94 compounds by library search and retention index, with 22 confirmed and quantified using authentic standards. Own-rooted Chambourcin differed from other root systems for multiple volatile compounds with fewer differences among grafted vines. For example, the average concentration of β-Damascenone present in own-rooted vines (9.49 µg/L) was significantly lower in other rootstocks (8.59 µg/L), whereas mean Linalool was significantly higher in 1103P rootstock compared to own-rooted. β-Damascenone was higher in regulated deficit irrigation (RDI) than other treatments. The approach outlined not only was shown to be useful for scientific investigation, but also in creating a protocol for analysis that would ensure differences of interest to the industry are not missed.
Highlights
Volatile composition plays a critical role in grape and wine quality and can capture information encompassing a year of vine growth in relation to its environment
The complexity of plant samples poses problems such as compound coelution despite effective prior chromatographic separation that complicates their discrimination. While these assumptions may be accurate in well-studied plants and foods such as V. viniferabased wines, poorly studied food such as wines made from interspecific hybrids benefit from a more holistic approach to data collection to avoid missing key analytes [29,41]
It is appropriate to adopt inclusive initial analysis to avoid missing differences induced by the treatments, before deciding what compounds are of interest (Figure 1)
Summary
Volatile composition plays a critical role in grape and wine quality and can capture information encompassing a year (or more) of vine growth in relation to its environment. In some metabolomic investigations, focus is first placed on those compounds that show the largest concentration difference as this indicates metabolic importance in aroma chemistry; this may miss critical changes in quality (Figure 1) [8,9] This is why often, in flavor work, a quantitative, targeted approach is taken to ensure perception threshold and other elements where actual concentration can be used to interpret the data. Targeted analysis of specific metabolites has been traditionally used to understand wine aroma and to decouple the effect of different factors on fruit and wine quality This approach involves identifying a selection of compounds from the chromatogram and quantifying those compounds in order to perform comparative analysis of the metabolic phenotypes using multivariate statistics (Figure 1). Our workflow goes forward to integrate the components of the targeted approach where the significant compounds are confirmed with the authentic standards and quantified so that the data is meaningful and interpretative in the real field situations (Figure 1)
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