Thomas S. Collins

Associations among Wine Grape Microbiome, Metabolome, and Fermentation Behavior Suggest Microbial Contribution to Regional Wine Characteristics

ABSTRACT Regionally distinct wine characteristics (terroir) are an important aspect of wine production and consumer appreciation. Microbial activity is an integral part of wine production, and grape and wine microbiota present regionally defined patterns associated with vineyard and climatic conditions, but the degree to which these microbial patterns associate with the chemical composition of wine is unclear. Through a longitudinal survey of over 200 commercial wine fermentations, we demonstrate that both grape microbiota and wine metabolite profiles distinguish viticultural area designations and individual vineyards within Napa and Sonoma Counties, California. Associations among wine microbiota and fermentation characteristics suggest new links between microbiota, fermentation performance, and wine properties. The bacterial and fungal consortia of wine fermentations, composed from vineyard and winery sources, correlate with the chemical composition of the finished wines and predict metabolite abundances in finished wines using machine learning models. The use of postharvest microbiota as an early predictor of wine chemical composition is unprecedented and potentially poses a new paradigm for quality control of agricultural products. These findings add further evidence that microbial activity is associated with wine terroir. IMPORTANCE Wine production is a multi-billion-dollar global industry for which microbial control and wine chemical composition are crucial aspects of quality. Terroir is an important feature of consumer appreciation and wine culture, but the many factors that contribute to terroir are nebulous. We show that grape and wine microbiota exhibit regional patterns that correlate with wine chemical composition, suggesting that the grape microbiome may influence terroir. In addition to enriching our understanding of how growing region and wine properties interact, this may provide further economic incentive for agricultural and enological practices that maintain regional microbial biodiversity. Wine production is a multi-billion-dollar global industry for which microbial control and wine chemical composition are crucial aspects of quality. Terroir is an important feature of consumer appreciation and wine culture, but the many factors that contribute to terroir are nebulous. We show that grape and wine microbiota exhibit regional patterns that correlate with wine chemical composition, suggesting that the grape microbiome may influence terroir. In addition to enriching our understanding of how growing region and wine properties interact, this may provide further economic incentive for agricultural and enological practices that maintain regional microbial biodiversity.

The combined impact of vineyard origin and processing winery on the elemental profile of red wines

The combined effects of vineyard origin and winery processing have been studied in 65 red wines samples. Grapes originating from five different vineyards within 40 miles of each other were processed in at least two different wineries. Sixty-three different elements were determined with inductively coupled-plasma mass spectrometry (ICP-MS), and wines were classified according to vineyard origin, processing winery, and the combination of both factors. Vineyard origin as well as winery processing have an impact on the elemental composition of wine, but each winery and each vineyard change the composition to a different degree. For some vineyards, wines showed a characteristic elemental pattern, independent of the processing winery, but the same was found for some wineries, with similar elemental pattern for all grapes processed in these wineries, independent of the vineyard origin. Studying the combined effects of grapegrowing and winemaking provides insight into the determination of geographical origin of red wines.

Developmental and metabolic plasticity of white-skinned grape berries in response to Botrytis cinerea during noble rot

Noble rot causes major reprogramming of grape berry metabolism by activating stress responses and ripening processes, including pathways that are inactive or with limited flux in white-skinned berries. Noble rot results from exceptional infections of ripe grape (Vitis vinifera) berries by Botrytis cinerea. Unlike bunch rot, noble rot promotes favorable changes in grape berries and the accumulation of secondary metabolites that enhance wine grape composition. Noble rot-infected berries of cv Sémillon, a white-skinned variety, were collected over 3 years from a commercial vineyard at the same time that fruit were harvested for botrytized wine production. Using an integrated transcriptomics and metabolomics approach, we demonstrate that noble rot alters the metabolism of cv Sémillon berries by inducing biotic and abiotic stress responses as well as ripening processes. During noble rot, B. cinerea induced the expression of key regulators of ripening-associated pathways, some of which are distinctive to the normal ripening of red-skinned cultivars. Enhancement of phenylpropanoid metabolism, characterized by a restricted flux in white-skinned berries, was a common outcome of noble rot and red-skinned berry ripening. Transcript and metabolite analyses together with enzymatic assays determined that the biosynthesis of anthocyanins is a consistent hallmark of noble rot in cv Sémillon berries. The biosynthesis of terpenes and fatty acid aroma precursors also increased during noble rot. We finally characterized the impact of noble rot in botrytized wines. Altogether, the results of this work demonstrated that noble rot causes a major reprogramming of berry development and metabolism. This desirable interaction between a fruit and a fungus stimulates pathways otherwise inactive in white-skinned berries, leading to a greater accumulation of compounds involved in the unique flavor and aroma of botrytized wines.

Artifactual Signal Splitting in the Capillary Electrophoresis Analysis of Organic Acids in Wine

An artifactual signal splitting was observed for acetic acid during the capillary zone electrophoresis of wine acids. Further study revealed that other comparably weak acids, propionic and butyric, show a similar split. Stronger carboxylic acids, formic, tartaric, malic, citric, and lactic acids showed no artifactual signal splits under the analysis conditions. Succinic acid showed intermediate behavior. The signal splitting could be eliminated by reducing the sample size and/or by employing the background electrolyte as the diluant.

Profiling of nonvolatiles in whiskeys using ultra high pressure liquid chromatography quadrupole time-of-flight mass spectrometry (UHPLC–QTOF MS)

Commercial samples of 63 American whiskeys, including bourbon whiskeys, Tennessee whiskeys, rye whiskeys and other blended whiskeys were analysed using ultra high pressure liquid chromatography (UHPLC) coupled with quadrupole time-of-flight (QTOF) mass spectrometry (MS). The non-volatile composition of the whiskeys was used to model differences among the samples using discriminant analysis. The blended American whiskeys were readily distinguished from the remaining types. Additionally, most Tennessee whiskeys could be differentiated from bourbon and rye whiskeys. Similarly, younger (<4 years old) and older (>8 years old) whiskeys could be separated. The compounds important for differentiating among these whiskeys included wood derived phenolic compounds, lignan derived compounds and several C8 and larger lipids. A number of additional compounds differentiated the whiskeys but could not be identified using MS and MS/MS data alone.

High-Throughput, Sub ng/L Analysis of Haloanisoles in Wines Using HS-SPME with GC-Triple Quadrupole MS

Haloanisole contamination causes development of “cork taint,” a musty off-aroma in affected wines. Cork taint results in significant economic loss for the wine and allied industries every year, therefore extensive quality-control procedures have been established at wineries and cork production facilities to monitor levels of haloanisoles in cork products. Because of the extremely low human sensory thresholds for these compounds (~1 to 4 ng/L for 2,4,6-trichloroanisole in wine), highly sensitive analytical methods are needed to detect the haloanisoles at threshold concentrations or lower. We present a method for the simultaneous analysis of four haloanisoles in wine—2,4,6-trichloroanisole (TCA); 2,3,4,6-tetrachloroanisole (TeCA); 2,3,4,5,6-pentachloroanisole (PCA); and 2,4,6-tribromoanisole (TBA)—that have been frequently associated with cork taint aromas in wines. Headspace solid-phase microextraction (HS-SPME) coupled to a GC-triple quadrupole MS was used to obtain limits of quantification that were ≤1.0 ng/L and below sensory threshold levels. The method is fully automated, requires no sample preparation other than the addition of internal standards, and is high throughput, with a 10-min extraction time and a 5-min incubation prior to extraction. This method can be readily adapted to screen for haloanisoles in cork extracts.