From microbial communities to aroma profiles: A comparative study of spontaneous fermentation in merlot and cabernet sauvignon wines

Abstract

This study aimed to compare the microbial community composition and aroma characteristics during the fermentation of different grape cultivars, Merlot and Cabernet Sauvignon. Principal Component Analysis (PCA), Partial Least Squares Discriminant Analysis (PLS-DA), and Odor Activity Value (OAV) screening identified 15 distinct active compounds. The sensory evaluation indicated that Merlot wine exhibited a more intense fruity aroma and received higher overall scores than Cabernet Sauvignon wine. High-throughput sequencing (HTS) results revealed that the microbial diversity in Merlot was higher than in Cabernet Sauvignon wine. Lachancea, Acremonium, Fructobacillus, and Lactiplantibacillus were unique to the Merlot wine, whereas Penicillium, Wickerhamomyces, Gluconobacter, and Klebsiella were exclusive to Cabernet Sauvignon wine. Saccharomyces and Tatumella were identified as the dominant microorganisms during the fermentation of both Merlot and Cabernet Sauvignon wines. Correlation analysis demonstrated a significant positive association among the dominant microbial communities, which played a crucial role in determining the formation of volatile compounds.

Keywords: 3-Methyl-1-butanol (PubChem CID31260); Different cultivars; Ethyl acetate (PubChem CID176); Ethyl caprate (PubChem CID8048); Ethyl caprylate (PubChem CID7799); Ethyl hexanoate (PubChem CID31265); Isobutyl acetate (PubChem CID8038); Linalool (PubChem CID6549); Phenethyl alcohol (PubChem CID6054); Spontaneous fermentation; Volatile aromas; Wine microbiome; Wine terroir.

Graphical abstract

Fig. 1

Physicochemical changes during the natural fermentation processes of Merlot (XM) and Cabernet Sauvignon (XC): (A) Total sugar, (B) Ethanol content, (C) Total acidity, (D) Volatile acidity, (E) pH, (F) Malic acid, (G) YAN (yeast assimilable nitrogen), (H) Citric acid, and (I) Tartaric acid. F0: Pre-fermentation (destemmed and crushed grape juice). F1: Early fermentation stage (approximately one-third of total sugar consumed). F2: Mid-fermentation stage (approximately two-thirds of total sugar consumed). F3: End of fermentation stage (total sugar <4 g/L). a-d: Different letters indicate significant differences (P < 0.05).

Fig. 2

Dynamic changes in volatile compound contents during the natural fermentation of Merlot and Cabernet Sauvignon: (A) Changes in the concentration of different types of volatile compounds; (B) Changes in the percentage composition of volatile compounds; (C) Principal component analysis (PCA) score plot; (D) Hierarchical cluster analysis (HCA); (E) Partial least squares discriminant analysis (PLS-DA) score plot; (F) Results of 200-time permutation tests for the PLS-DA model (R² = 0.259, Q² = −0.675); (G) Venn diagram showing the number of shared and unique volatile compounds in Merlot and Cabernet Sauvignon, with overlapping regions indicating the number of shared compounds; (H) Heatmap of 16 differential compounds (VIP > 0.1, P < 0.05); (I) Variable importance in projection (VIP) scores of differential volatile compounds between grape cultivars calculated via PLS-DA and the Log2 fold change of 15 differential volatile flavor compounds during the natural fermentation of Merlot and Cabernet Sauvignon.

Fig. 3

Microbial diversity analysis during the natural fermentation of Merlot (XM) and Cabernet Sauvignon (XC): (A) Richness indices for Merlot and Cabernet Sauvignon: fungal Chao1 and Observed-species indices, bacterial Chao1 and Observed_species indices; (B) Diversity indices for Merlot and Cabernet Sauvignon: fungal Simpson and Shannon indices, bacterial Simpson and Shannon indices; (C) Principal coordinate analysis (PCoA) of fungal community Bray-Curtis distances and bacterial community Unweighted UniFrac distances for Merlot and Cabernet Sauvignon. (D, E) Shared fungal OTUs during the natural fermentation of Merlot and Cabernet Sauvignon; (F, G) Shared bacterial OTUs during the natural fermentation of Merlot and Cabernet Sauvignon.

Fig. 4

Microbial community distribution patterns during the natural fermentation of Merlot (XM) and Cabernet Sauvignon (XC): (A) Stacked bar chart showing changes in the relative abundance of dominant fungal taxa during the fermentation processes of Merlot and Cabernet Sauvignon; (D) Stacked bar chart showing changes in the relative abundance of dominant bacterial taxa during the fermentation processes of Merlot and Cabernet Sauvignon; (B) Phylogenetic tree illustrating the taxonomic relationships of major fungal taxa during the natural fermentation of Merlot and Cabernet Sauvignon. (E) Phylogenetic tree illustrating the taxonomic relationships of major bacterial taxa during the natural fermentation of Merlot and Cabernet Sauvignon; (C) Bar chart showing fungal taxa with significant differences during the natural fermentation of Merlot and Cabernet Sauvignon; (F) Bar chart showing bacterial taxa with significant differences during the natural fermentation of Merlot and Cabernet Sauvignon.

Fig. 5

Network diagrams illustrating the co-occurrence and exclusion relationships among microbial taxa at the genus level during the natural fermentation of Merlot (A) and Cabernet Sauvignon (B) (|r| > 0.6, P < 0.05): Oval nodes represent microbial taxa. The color of the lines indicates the type of relationship: red lines represent positive correlations, while blue lines represent negative correlations. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 6

Correlation analysis between dominant microbial genera and key volatile compounds in Merlot (A) and Cabernet Sauvignon (B) (P < 0.05): Lines connecting nodes represent correlations; Red lines between circles indicate positive correlations, while blue lines indicate negative correlations; The size of the circles represents the number of associated variables; larger circles indicate more associated variables; The thickness of the lines represents the strength of the correlation; thicker lines indicate stronger correlations. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)