An efficient methodology for modeling to predict wine aroma expression based on quantitative data of volatile compounds: A case study of oak barrel-aged red wines

Dynamic changes in dissolved oxygen concentration, microbial communities, and volatile compounds during industrial oak-barrel fermentation of Sauvignon Blanc wine

Oak-barrel fermentation is used in white wine production to enhance aroma and flavor complexity. However, the dynamics of microbial communities and their impact on the formation of flavor compounds during barrel fermentation remain unclear. This study investigated the changes in dissolved oxygen concentrations, microbial communities, and volatile compounds during Sauvignon Blanc wine fermentation in various oak barrels (new and two-year-old Francois Freres and new Taransaud) and stainless-steel tanks. We found that oak barrels had higher dissolved oxygen levels than steel tanks, with new barrels exhibiting higher levels than the old ones during fermentation. The dominant bacterial genera across all the vessels during the fermentation included Ralstonia, Pantoea, Gluconobacter, and Mesorhizobium, whereas the dominant fungal genera were Saccharomyces, Aspergillus, Alternaria, and Aureobasidium. The fermentation environment altered the microbial composition as the fermentation progressed in various vessels. Compared with steel tanks, difference in microbial composition between oak barrels was less significant. The new oak barrels increased the levels of esters, alcohols, and acids in the wine, while only minor differences were observed between old barrels and steel tanks. Correlation analysis showed that Ralstonia, Gluconobacter, Mesorhizobium, and Saccharomyces were positively correlated with the production of wine volatiles. Structural equation modeling indicated the interactions between dissolved oxygen, microbial communities, and wine aromas. The impact of dissolved oxygen on fungal communities during fermentation differed significantly between new and old oak barrels, indirectly influencing aroma. Conversely, in stainless-steel tanks, dissolved oxygen weakly influenced the bacterial and fungal communities, with the influence on wine aroma primarily dependent on the fungal communities. These findings provide valuable insights for optimizing the Sauvignon Blanc wine fermentation in oak barrels.

Effect of different inoculation strategies of mixed culture Saccharomyces cerevisiae/Oenococcus oeni on the aroma quality of Chardonnay wine

There has been growing interest in the use of mixed cultures comprised of Oenococcus oeni and Saccharomyces cerevisiae to produce wine with local style and typicality. This study has investigated the influence of the inoculation protocol of O. oeni on the fermentation kinetics and aromatic profile of Chardonnay wine. The one selected autochthonous O. oeni strain (ZX-1) inoculated at different stages of the alcoholic fermentation process successfully completed malolactic fermentation (MLF). Co-inoculum of S. cerevisiae and O. oeni enabled simultaneous alcoholic fermentation and MLF, leading to at least a 30 % reduction in the total fermentation time when compared to the sequential inoculation process, which was attributed to the lower ethanol stress. Meanwhile, co-inoculum stimulated the accumulation of volatile aroma compounds in Chardonnay wine. In particular, the mixed modality where the O. oeni strain ZX-1 was inoculated 48 h after S. cerevisiae allowed higher levels of terpenes, acetates, short-chain, and medium-chain fatty acid ethyl esters to be produced, which may result in the enhanced floral and fruity attributes of wine. Aroma reconstitution and omission models analysis revealed that the accumulation of linalool, geraniol, isoamyl acetate, ethyl hexanoate, and ethyl caprylate during the mixed fermentation process enhanced the stone fruit, tropical fruit, and citrus aromas in Chardonnay wine. Therefore, the simultaneous fermentation of S. cerevisiae and autochthonous O. oeni ZX-1 has a positive effect on MLF and contributes to producing wines with distinctive style.

An efficient artificial intelligence algorithm for predicting the sensory quality of green and black teas based on the key chemical indices

The key components dominating the quality of green tea and black tea are still unclear. Here, we respectively produced green and black teas in March and June, and investigated the correlations between sensory quality and chemical compositions of dry teas by multivariate statistics, bioinformatics and artificial intelligence algorithm. The key chemical indices were screened out to establish tea sensory quality-prediction models based on the result of OPLS-DA and random forest, namely 4 flavonol glycosides of green tea and 8 indices of black tea (4 pigments, epigallocatechin, kaempferol-3-O-rhamnosyl-glucoside, ratios of caffeine/total catechins and epi/non-epi catechins). Compared with OPLS-DA and random forest, the support vector machine model had good sensory quality-prediction performance for both green tea and black tea (F1-score > 0.92), even based on the indices of fresh tea leaves. Our study explores the potential of artificial intelligence algorithm in classification and prediction of tea products with different sensory quality.

Differences in Aroma Profile of Cabernet Sauvignon Grapes and Wines from Four Plots in Jieshi Mountain Region of Eastern China

The Bohai Bay region is a famous wine-growing area in China, where the rainfall is concentrated in the summer due to the influence of the temperate semi-humid monsoon climate. As such, the vineyard terrain has a significant impact on the flavor quality of the grapes and the resulting wines. To explore the relationship between the 'Cabernet Sauvignon' wine style and terrain, this study takes four different plots in the Jieshi Mountain region to investigate the differences in the aroma profile of Cabernet Sauvignon grapes and wines of two consecutive vintages. Based on two-way ANOVA, there were 25 free and 8 glycosylated aroma compounds in the grapes and 21 and 10 aroma compounds with an odor activity value greater than 0.1 in the wines at the end of alcohol fermentation (AF) and malolactic fermentation (MLF), respectively, that varied among the four plots. Wines from the four plots showed a significant difference in floral and fruity aroma attributes, which were mainly related to esters with high odor activity values. The difference in concentration of these compounds between plots was more pronounced in 2021 than in 2020, and a similar result was shown on the Shannon-Wiener index, which represents wine aroma diversity. It has been suggested that high rainfall makes the plot effect more pronounced. Pearson's correlation analysis indicated that concentrations of (E)-3-hexen-1-ol in grapes and ethyl 3-methylbutanoate, ethyl hexanoate, isoamyl acetate, isopentanoic acid, and phenethyl acetate in wines were strongly positively correlated with the concentrations of N, P, K, Fe, and electrical conductivity in soil but negatively correlated with soil pH. This study laid a theoretical foundation for further improving the level of vineyard management and grape and wine quality in the Jieshi Mountain region.

Comparison of Chemical and Sensory Profiles between Cabernet Sauvignon and Marselan Dry Red Wines in China

The differences in chemical and sensory characteristics between Marselan and Cabernet Sauvignon in China were investigated with gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography-triple quadrupole mass spectrometry (HPLC-QqQ-MS/MS), combined with color parameters and sensory data. The paired t-test results showed that terpenoids, higher alcohols, and aliphatic lactones were significantly different according to the grape variety. Meanwhile, terpenoids could be considered as marker aroma compounds to distinguish Marselan wines from Cabernet Sauvignon, which could explain the distinct floral note in Marselan wines. The mean concentrations of the mv-vsol, mv-vgol, mv-vcol, mvC-vgol, mv-v(e)cat, mvC-v(e)cat, mv-di(e)cat, and cafA were higher in Marselan wines than Cabernet Sauvignon wines, and these compounds might confer Marselan wines with a deeper color, more red hue, and higher tannin quality. The phenolic profiles of Marselan and Cabernet Sauvignon wines were influenced by the winemaking process, mitigating the varietal differences. As for sensory evaluation, the intensities of herbaceous, oak, and astringency of Cabernet Sauvignon were more pronounced than Marselan, whereas the Marselan wines were characterized by a high color intensity and more redness, together with floral, sweet, and roasted sweet potato attributes, and tannin roughness.