Photoselective shading is a process that modulates the radiation intensity in specific regions of the electromagnetic spectrum. It is a common practice in horticulture to manipulate specific plant physiological responses, but to date has only received minimal attention in viticulture. The potent odorant 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN) is of particular relevance for aged Riesling wine, which are also known to be impacted by the magnitude of bunch zone light exposure during berry development. Hence, in this study, the effect of photoselective bunch zone shading on the formation of TDN in wine was investigated across two consecutive growing seasons. Applying red, black or green shade cloth (SC) to the bunch zone provided unique bunch zone light environments and yielded distinct differences in grape and wine composition compared with the unshaded control. Overall, bunch zone shading through shade cloth was effective in reducing overall photosynthetically active radiation compared to the control and the photoselectivity of the SC treatments differently affected a number of grape and wine measures. Fruit yield was somewhat but not significantly lower under black SC treatments, while juice pH was increased in grapes grown under green and black SC across both vintages compared to the control. Both grape sugar accumulation (P = 0.035) and ammonia nitrogen (P = 0.043) showed evidence of treatment effects, although with low F-statistics (4 and 3, respectively). Measures of hydrolytically released TDN in juice and free TDN concentrations in wine were lower in SC treatments. Unexpectedly, sensory descriptive analysis of the wines demonstrated that increased ‘kerosene-like’ aroma was not consistently associated with free TDN concentrations in wine. In summary, photoselective bunch shading was demonstrated to be an effective method for manipulating grape and wine outcomes and may aid in overcoming viticultural obstacles and quality impacts associated with climate change.
Ruminants produce large amounts of the greenhouse gas, methane, which can be reduced by supplementing feed with products that contain anti-methanogenic compounds, such as the solid winemaking by-product, grape marc. The aim of this study was to exploit compositional differences in grape marc to better understand the roles of condensed tannin and fatty acids in altering methanogenesis in a ruminant system. Grape marc samples varying in tannin extractability, tannin size and subunit composition, and fatty acid or tannin concentrations were selected and incubated in rumen fluid using an in vitro batch fermentation approach with a concentrate-based control. Four distinct experiments were designed to investigate the effects on overall fermentation and methane production. Generally, fatty acid concentration in grape marc was associated with decreased total gas volumes and volatile fatty acid concentration, whereas increased condensed tannin concentration tended to decrease methane percentage. Smaller, extractable tannin was more effective at reducing methane production, without decreasing overall gas production. In conclusion, fatty acids and tannin concentration, and tannin structure in grape marc play a significant role in the anti-methanogenic effect of this by-product when studied in vitro. These results should be considered when developing strategies to reduce methane in ruminants by feeding grape marc.
The winemaking by-product grape marc (syn. pomace) contains significant quantities of latent flavour in the form of flavour precursors which can be extracted and used to modulate the volatile composition of wine via chemical hydrolysis. Varietal differences in grapes are widely known with respect to their monoterpene content, and this work aimed to extend this knowledge into differences due to cultivar in volatiles derived from marc precursors following wine-like storage conditions. Marc extracts were produced from floral and non-floral grape lots on a laboratory-scale and from Muscat Gordo Blanco marc on a winery -scale, added to a base white wine for storage over five to six months, before being assessed using a newly developed membrane-assisted solvent extraction gas chromatography-mass spectrometry (GC-MS) method. The geraniol glucoside content of the marc extracts was higher than that of juices produced from each grape lot. In all wines with added marc extract from a floral variety, geraniol glucoside concentration increased by around 150–200%, with increases also observed for non-floral varieties. The relative volatile profile from extracts of the floral varieties was similar but had varied absolute concentrations. In summary, while varietally pure extracts would provide the greatest control over flavour outcomes when used in winemaking, aggregated marc parcels from floral cultivars may provide a mechanism to simplify the production logistics of latent flavour extracts for use in the wine sector.
A method for determining ethyl coumarate and ethyl ferulate in wine using GC-MS with deuterium-labeled analogues has been developed and used to measure the evolution of these two esters during the production of two commercial monovarietal red wines, cv. Grenache and Shiraz. During fermentation, the concentration of ethyl coumarate rose from low levels to 0.4 mg/L in Grenache and 1.6 mg/L in Shiraz wines. These concentrations then increased further during barrel aging to 1.4 and 3.6 mg/L, respectively. The concentration of ethyl ferulate was much lower, reaching a maximum of only 0.09 mg/L. Conversion of ethyl coumarate and ethyl ferulate to their corresponding ethylphenols was observed during fermentations of a synthetic medium with two strains of Dekkera bruxellensis (AWRI 1499 and AWRI 1608), while a third (strain AWRI 1613) produced no ethylphenols at all from these precursors. Strains AWRI 1499 and 1608 produced 4-ethylphenol from ethyl coumarate in 68% and 57% yields, respectively. The corresponding yields of 4-ethylguaiacol from ethyl ferulate were much lower, 7% and 3%. Monitoring of ethyl coumarate and ethyl ferulate concentration during the Dekkera fermentations showed that the selectivity for ethylphenol production according to yeast strain and the precursor was principally a result of variation in esterase activity. Consequently, ethyl coumarate can be considered to be a significant precursor to 4-ethylphenol in wines affected by these two strains of Brettanomyces/Dekkera yeast, while ethyl ferulate is not an important precursor to 4-ethylguaiacol.
To determine the optimum methods for determining condensed tannin (CT) content in grape marc, butanol-hydrochloric acid assays and phloroglucinolysis were adapted for use, applied to a range of grape marc types, and the methods compared. Porter's assay (butanol-HCl) was found to give unreliable results due to nonlinear color responses to grape skin and seed tannin concentrations, whereas the modification to include acetone (Grabber's assay) overcame this. Differences between skin and seed tannin responses highlighted the need to adequately select the correct grape tannin standard, and the formation of pH-dependent color was accounted for through acidification of blank samples. For phloroglucinolysis, the inability to remove highly bound tannins from cell wall material was highlighted, although a measure of tannins remaining post-phloroglucinolysis (Grabber's assay) showed a trend with the level of exposure to oxidative storage or processing conditions. The comparison of CT concentrations from phloroglucinolysis and Grabber's assay gave poor correlation coefficients.
Theoretical investigations on the treatment of bicyclic endoperoxides (1,2-dioxines) with ozone at the HF/6–31G*, MP2/6–31G* or 6–311G*, and DFT(B3LYP)/6–31G* levels of theory indicate that the estimated activation energies for formation of the possible endo-endo, endo-exo, exo-endo, or exo-exo transition states along with the formation of the primary ozonides and product ozonides are very sensitive to effects of electron correlation and basis set. This study suggests that MP2/6–311G* is the best level of theory for evaluating such systems. At the MP2/6–311G* level of theory it was found that the transition state for primary ozonide formation was lowest in energy when ozone approaches in an endo facial fashion with a further 3 kJ mol–1 stabilisation seen when the central oxygen within the primary ozonide protrudes outwards (exo) as opposed to inwards (endo). The product ozonides are predicted to be more stable than the combined starting materials by some 380–580 kJ mol–1 depending on the level of theory, clearly highlighting the substantive exothermic nature of this type of ozonolysis reaction.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
In the title mol-ecule, C(24)H(32)O(10), one tert-butyl ester group is folded towards the central benzene ring while the other is directed away. The acetyl group is almost perpendicular to the benzene ring to which it is connected [C-C-O-C torsion angle = 90.4 (12)°]. The conformation about the ethene bond [1.313 (7) Å] is E. The atoms of the benzene ring and its attached ester group and part of the hy-droxy tert-butyl ester side chain are disordered over two sets of sites in a 50:50 ratio. Linear supra-molecular chains along the a axis mediated by hy-droxy-carbonyl O-H⋯O hydrogen bonds feature in the crystal packing. The same H atom also partakes in an intra-molecular O-H⋯O inter-action.
The title compound, C23H30O9, has an approximate T-shape with the tert-butyl ester groups lying either side of the benzene ring. The acetyl group is almost perpendicular to the benzene ring to which it is connected [C—C—O—C torsion angle = −106.7 (3)°]. The conformation about the C=C double bond [1.331 (4) Å] is E. Linear supramolecular chains along the a axis mediated by hydroxy–carbonyl O—H⋯O hydrogen bonds feature in the crystal packing. The same H atom is also involved in an intramolecular O—H⋯O interaction.
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