The total run time per sample was 61.67min. Electron ionization was performed with a source temperature of 230o C and the quadrupole at 150o C. The wine samples were measured using synchronous scan and selected ion monitoring . The mass spectrometer scanned from m/z 40 to 300. Compounds were detected using between two and six selected ions. Data was analyzed using MassHunter Qualitative Analysis software . After normalization with 2-undecanone internal standard, results were expressed as peak areas. Compounds were tentatively identified in the mass spectrometry spectrum of the peaks and confirmed by comparison to the National Institute of Standards and Technology database . The ions used SIM for each compound and retention times were reported previously by . The odor activity value thresholds were obtained from a selected review of published literature of young red wines and were used in comparing the monitored compounds . Meteorological data collection and climactic conditions at the experimental site for the 2020 and 2021 growing seasons are described in detail by Marigliano et al. . Briefly, there were 1762.7°C growing degree days accumulated in 2020 compared to 1572.3°C GDDs accumulated in 2021, with similar GDD accumulation from April to June in both years. Compared to the 10-year average , the 2020 growing season accumulated more growing degree days by 1 October. The 2021 growing season was a cooler year with less accumulated GDD than the 10-year average. The total precipitation at the experimental site from 1 March 2020 to 30 September 2020 was 84.1mm, a notable 100.5mm less precipitation than the 10-year average for the experimental site. Drought conditions continued into the 2021 water year, growing blueberries in containers with 66.9 mm of precipitation between 1 March 2021 and 30 September 2021.
Precipitation only occurred in March and April 2021 and was negligible in the following months. Given the severe drought conditions in both experimental years, precipitation had a negligible effect on plant water status in control and shaded treatments with 25% ETc replacement, as demonstrated by no significant effects on stem water potential integrals between control and shaded treatments in either experimental year .Grapes resulting from field treatments were vinified under the same conditions in both years. In 2020 alcohol content was the highest in D1 and D4 wines , while alcohol content and residual sugar concentration was lowest in C0 in 2020. All shade film wines contained more alcohol and residual sugar than C0. In 2021, alcohol content and residual sugar concentration was unaffected across all wines. In 2020, pH was only decreased in D3 wines. In 2021, C0 wines had the lowest pH compared wines from shaded grapes. Among the shaded treatments, D4 and D5 wines had higher pH compared to D1 and D3 wines. In 2020, titratable acidity only increased in D3 wines compared to C0, D1 and D5 wines. C0, D1, D4 and D5 wines were indistinguishable in titratable acidity. While C0 had one of the lowest values for TA in 2020, C0 wines in 2021 had one of the highest TA values, along with D3 and D5 wines. The lowest TA value was observed in D4 wines from 2021. Color intensity within the 2020 wines varied considerably, with the D4 having the greatest value for CI . In 2021, D4 again had the highest values for CI, while the remaining wines were statistically not different from each other. Hue decreased only in D3 wines during the 2020 vintage, while there was no effect of shade films of wine hue during the 2021 vintage . The trend for the percentage of polymeric anthocyanins was consistent in both vintages. D1 and D4 had the highest percentage of polymeric anthocyanins, while D5, D3and C0 wines had less . In 2020, D1 and D4 wines had higher TPI values compared to C0 and D3 wines. In 2021, TPI of wines was not affected by shade films except for D4. 3.3 Wine flavonoid content and profile Wine anthocyanin profiles were separated into glucosides, 3-acetylated and coumarylated anthocyanins .
The total free anthocyanin concentration was the lowest in C0 wines compared to shade film treatments in 2020. Concentrations of 3-glucosides and 3-acteylated glucosides increased for all anthocyanins under shading treatments compared to C0, except for peonidin 3-acetyl-glucoside and cyanidin 3-glucoside in which shading treatments had no effect. The composition of coumarylated 3’4’5’-hydroxylated anthocyanin modifications was largely impacted by shading, with the largest concentrations detected in C0, D1 and D5 wines. Overall, the ratio of di- to tri-hydroxylated anthocyanins was the largest in C0 wines and the lowest in D5. Conversely in 2021, total free anthocyanin concentrations were the highest in D4, C0, and D1 wines. Anthocyanin modifications due to shading treatments were more varied in 2021 compared to 2020. Overall, wines from D4 had the most 3-glucosides and 3-acetylated glucosides, while C0 and D5 consistently had less. Coumarylated anthocyanin concentrations were reduced in D3 and D5 wines compared to C0 wines. This was not consistent with the concentrations observed in 2020. Likewise, there was no statistically significant effect on the anthocyanin hydroxylation ratio in 2021 wines, while shading had an impact on anthocyanin hydroxylation in wines in 2020. Nine flavonol compounds were monitored in wines using HPLC . For all monitored flavonol compounds except myricetin-3-glucuronide, C0 wines consistently had the highest concentrations in 2020 compared to shaded wines, with D4 and D5 wines following in flavonol concentration. Subsequently, C0 also had the highest wine flavonol concentration when calculated as total flavonols in 2020. A similar trend occurred in 2021. C0 wines from 2021 also contained greater concentrations of each flavonol compared to shaded treatments, as well as total flavonol concentration.The wine aroma profiles from the 2020 and 2021 vintages were analyzed with and 29 volatile compounds were identified and categorized into their respective compound classes . The aromas profiles of wines depended highly on vintage, resulting in distinct aroma profiles.
Generally, in 2020, total higher alcohols were unaffected by shade treatments, except for isoamyl alcohol and benzyl alcohol. Wines produced from shaded fruit had similar concentrations of isoamyl alcohol while the C0 had the lowest isoamyl alcohol concentration. Benzyl alcohol concentrations were reduced in D3 and D5 wines compared to C0, D1 and D4 wines. In 2021, shading treatments did not impact the concentration of higher alcohols in the resulting wines except for benzyl alcohol, which increased in 2021 D3 wines compared to all other treatments. Acetate esters and fatty acid ethyl esters showed varied effects in wines due to shading in 2020. C0 and D5 had the lowest ethyl acetate concentrations compared to the other shade treatments. Likewise, isoamyl acetate was reduced in C0, D4 and D5 wines compared to D1 and D3 wines. Among the shade film treatments , ethyl hexanoate and ethyl octanoate concentrations were comparable between D1 and D5 wines and were greater than concentrations found in D3 wines. C0 and D5 wines were indistinguishable in ethyl butyrate, ethyl-2-methylbutyrate and ethyl valerate in 2020, with D1 and D3 wines having the highest concentrations of each these ester compounds. Isobutyric acid increased in D4 in 2020. In 2021, there were no significant impacts of shading on acetate esters, fatty acid ethyl esters, ethyl butyrate, ethyl-2-methylbutyrate or ethyl valerate. The effect of shade films on various terpenes and norisoprenoids was highly dependent on vintage conditions. Alpha-terpinene was highest in D5 wines but was significantly reduced in D1 and D3 wines in 2020. The D4 wines had the most cis-rose-oxide while C0 wines had the least. Linalool concentrations were reduced in C0, D4 and D5 wines. Among the shaded treatments, nerol concentrations were enhanced in D5 wines in 2020, square pots while there was no effect of shading on nerol concentration in 2021. D5 did not differ from the C0 in nerol concentration in 2020. Farnesol in D3 was reduced in 2020 whereas farnesol concentrations were not affected in 2021 wines. Conversely, nerolidol was unaffected by shade films in 2020, whereas significant decreases in nerolidol concentrations were observed in D4 and D5 wines in 2021. It was observed that β-damascenone were elevated in 2020 in C0 wines, yet differences in β- damascenone concentrations were non-significant between shade film treatments. In 2021, only significant differences in β-damascenone concentrations were observed in wines, with C0 wines containing the most β-damascenone and D5 wines containing the least. β-ionone concentrations were not statistically significant between all treatments in 2020 and 2021. To determine the effects of partial solar shading on wine chemistry, flavonoid composition, and aromatic profiles of wines we conducted a principal components analysis for both vintages . In 2020, PCA indicated that PC1 accounted for 30.8%, and PC2 accounted for 22.1% of the total variance. The C0 treatments clustered together, separately from the partial solar shading treatments. The separation along PC1 was explained by the ratio of di- to tri-hydroxylated anthocyanins in wines, norisoprenoids and flavonols, as well as lower CI, alcohol content and TPI. The separation along PC2 was explained by TA, pH, terpenes and the percentage of polymeric anthocyanins in wine samples. In 2021, PCA indicated PC1 accounted for 29.9%, and PC2 accounted for 22.2% of the total variance. The C0 treatments again separated from shade film treatments, but less so than in 2020. The separation in PC1 was again explained by the ratio of di- to tri-hydroxylated anthocyanins, along with the total glucosides, total methylated anthocyanins, and total anthocyanins. The separation of C0 was along PC2 and thus was associated with higher concentrations of flavonols, terpenes, norisoprenoids, and polymeric anthocyanins in wine. We analyzed the relationships further between the variables monitored with a correlation analysis in wines . In 2020, CI in wines had the strongest positive correlation with TPI and acids .
Alcohol percentage and ketones were also positively correlated to TPI and acids, although less so than CI. Ketones also were very strongly positively correlated with higher alcohols, while higher alcohols were less strongly correlated to acids. Conversely, flavonols were strongly negatively correlated with acetate esters and other esters in wines. Norisporenoids and pH were less negatively correlated to acetate esters. Fatty acid ethyl esters particularly showed to be negatively correlated with TA. In 2021, the strongest positive correlations in wines were between total anthocyanins and total glucosides and total methylated anthocyanins . Total coumarylated anthocyanins were significantly and positively correlated to total anthocyanins, methylated anthocyanins, and total glucosides. Strong negative correlations were found between hue and ester compounds including fatty acid ethyl esters and acetate esters. A strong negative correlation existed between the ration of di- to tri-hydroxylated anthocyanins and total acetylated anthocyanins. Lastly, total higher alcohols and pH were strongly negatively correlated with each other. In hot viticulture regions, there is a desire to reduce excessive alcohol content in wines due to marketability and taxation concerns. Numerous studies have demonstrated that partial solar radiation exclusion is an effective method for reducing the amount of ethanol in wines by reducing TSS in shaded clusters . However, in the present study, C0 wines consistently had the lowest alcohol content and the lowest concentration of residual sugars in 2020 compared to shaded fruit, despite grapes at harvest having similar TSS values across the treatments . This may be due to the composition of sugars in the grape berry being affected by excessive cluster temperatures in C0 fruit. Sepúlveda and Kliewer showed that heat stress at 40°C post-veraison decreases glucose and fructose in the grape berry. During heat wave events post-veraison, cluster temperatures in C0 reached a maximum temperature of 58°C, exceeding the point at which glucose and fructose content is altered . Additionally, the production of non-fermentable sugars such as arabinose, raffinose and xylose are known to be present in the grape berry . Genes involved in the production of these sugars have been shown to be upregulated under heat stress conditions in grapevine . While the grape berry is 95-99% glucose and fructose at harvest, these non-fermentable sugars are included in the metric of total soluble solids . As a result, while TSS was unaffected by shade films , the proportion of fermentable to nonfermentable sugars may be impacted, thus leading to 2020 C0 wines with reduced alcohol content. This difference in alcohol content between 2021 wines was not observed most likely due to the 2021 growing season being cooler with less GDDs than 2020 .