First fruit: NMR characterisation of grape berries
Ezine
- Published: Feb 1, 2011
- Author: David Bradley
- Channels: NMR Knowledge Base
Berry nice NMRThe position in which a grape in a bunch matures on the vine seems to influence the production of different metabolites more than the specific genetic clone from which the vine is raised, according to new NMR data. Researchers have turned to NMR spectroscopy to help them analyse and characterise the chemistry of grape berries. The work could have important implications for agriculture and wine growers as it reveals that position in the bunch rather than grape clonal type affects metabolomics more. A fusion of experimental results, data analysis and extensive discussions between researchers working in the fields of chemistry, agronomy, biotechnology, spectroscopy and biostatistics has resulted in the molecular characterization of Sardinian Vermentino grape berries. The metabolic NMR profile of the berries was undertaken with a straightforward preparation so that, to all intents and purposes, the results are as close to the profile of the berries hanging on the vine as possible. The NMR reveals the variation of the metabolic profile of the berries as a function of the developmental stage of the fruit. In other words, NMR analysis has allowed the researchers to follow the metabolic changes that occur as the berries ripen; this is when the most important biochemical changes occur. "It is well known that many factors play roles in determining the value of a wine," explains team leader Roberto Anedda of Porto Conte Ricerche in Alghero, Italy. "In the clonal selection of grape cultivar, the pedoclimatic [soil and terrain] variables in the site where the vineyard is located and agronomical and enological practices affect grape growth." - He adds that much of the research concerned with grape analysis has been carried out on homogenates. In particular, analysis is carried out on partially fermented grape juices and subjected to the rapid and uncontrolled action of proteolytic enzymes. "In our work, a previously published extraction protocol for analyzing plants has been rearranged and adapted to the analysis of grapes," Anedda adds. He suggests that this approach leads to results unbiased by fermentation processes or sample preparation. Heard it on the grapevineThe team, which includes colleagues at the University of Sassari, Gilberto Mulas, Maria Grazia Galaffu, Luca Pretti, Gianni Nieddu, Luca Mercenaro and Roberto Tonelli investigated the metabolomic profile of a clonal selection of Vermentino grape berries, which have been studied widely in terms of their genetics and their agronomics but not on the chemical level. Vermentino is one of the most prominent wine grapes in Italy, being used in the fifth most popular wine for the general consumer in Italy. "Each clone of Vermentino is characterized by having a particular size, shape and morphology of the bunch and grape, variable productivity, typical flavours and different disease resistance," says Anedda. "In relation to the different geographic area selection, each clone evidenced dissimilar agronomic and technological performance." As such, choosing a suitable clone is commonly believed to be the most important first choice for winemakers towards producing high-quality wines. However, Anedda's NMR work would suggest that the received wisdom is not particularly relevant at the molecular level. The team harvested seven selections of Vermentino grapes from the same vineyard and carried out an unbiased extraction protocol. They analysed the extracts as a function of the clone, the position of berries in the bunch or growing area within the vineyard using quantitative NMR and statistical analysis (PCA, correlation analysis, Anova). "Significant variability of the amino acids such as arginine, proline, and organic acids (malic and citric) characterizes the rapid rearrangements of the metabolic profile in response to environmental stimuli," the team says. Metabolic grapes"The NMR data show that the metabolic status of the grapes is influenced strongly by factors other than clone types, such as environmental variables," Anedda says. "Indeed, the effect of the berry position within the bunch leads to a net differentiation among the berries analyzed." He points out that the position of a single grape within a bunch has more important to the resulting metabolic profile and putatively the quality of the wine than the variability induced by the clone and by the region of the vineyard. He explains this point on the basis that morphologic and genetic analysis are somewhat insensitive toward the current metabolic state of the plant, which changes very rapidly in response to environmental stimuli such as ground exposure to light and drought conditions during ripening.
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