Microbial community succession and volatile compounds changes during spontaneous fermentation of Cabernet Sauvignon (Vitis vinifera L.) under rain-shelter cultivation

Abstract

Microbiota succession in spontaneous fermentation of Cabernet Sauvignon cultivated under the rain-shelter was characterized, with open-field cultivation as the control. For both cultivation modes, Saccharomyces, Starmerella, and Mycosphearella were the principal fungi, and Tatumella, Gluconobacter, and Acinetobacter were the prevailing bacteria. Rain-shelter reduced the abundance of Hanseniaspora, Candida, Starmerella, Gluconobacter, and Lactococcus. During fermentation, fungal microbiota diversity in samples from the rain-shelter cultivation decreased more drastically than the control (p < 0.05). In terms of the correlation between microbiota and volatile compounds production, the abundance of Hanseniaspora uvarum, Candida apicola, Starmerella bacillaris, Gluconobacter oxydans, and Lactococcus lactis were positively correlated with the production of esters and higher alcohols. Instead of bacterial microbiota, fungal community succession exhibited a positive correlation with the final wine volatiles under the rain-shelter cultivation. These findings demonstrated rain-shelter cultivation influences the succession pattern of microbial communities and in turn impacts the wine aromas and flavors.

Keywords: Correlation analysis; Flavor; Microbial diversity; Spontaneous fermentation; Volatile compounds.

Graphical abstract

Fig. 1

Main microbial community compositions in grape juices harvested from two cultivation modes. S: rain-shelter mode; O: open-filed mode. The species abundance of fungal (a) and bacterial (b) communities were characterized at the genus level (Welch’s t-test, p-value ≤ 0.05). Random forest analysis based on Mean Decrease Gini determined significant discriminatory taxa of fungal (c) and bacterial (d) microbiota associated with the cultivation modes.

Fig. 2

Fungal community succession during spontaneous fermentation of grapes harvested under two cultivation modes. BF: at the beginning of alcoholic fermentation; MF: in the middle of alcoholic fermentation; EF: at the end of alcoholic fermentation. (a) The dominant fungal species were characterized at the genus level in the fermentation process. (b) Comparison of fungal diversity under two cultivation modes during fermentation (Tukey-HSD test, p < 0.05); different letters indicate significant differences between the two treatments. (c) PCoA analysis (Bray-Curtis distances) of fungal species distribution (OTUs) under two cultivation modes during fermentation. Identification of discriminant fungal taxa in the middle (d) and at the end (e) of fermentation under two cultivation modes by LEfSe (SMF vs. OMF; SEF vs. OEF; Kruskal-Wallis and rank test α < 0.05; LDA score > 2.00). S: rain-shelter mode, green color-coded; O: open-filed mode, red color-coded. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 3

Bacterial community succession during spontaneous fermentation of grapes harvested under two cultivation modes. S: rain-shelter mode; O: open-filed mode. BF: at the beginning of alcoholic fermentation; MF: at the middle of alcoholic fermentation; EF: at the end of alcoholic fermentation. (a) The dominant bacterial species were characterized at the genus level in the fermentation process. (b) Comparison of bacterial diversity under the two cultivation modes during fermentation (Tukey-HSD test, p < 0.05); different letters indicate significant differences between treatments. (c) PCoA analysis (Bray-Curtis distances) of bacterial species distribution (OTUs) under two cultivation modes during fermentation. Identification of discriminant bacterial taxa in the beginning (d) and middle (e) of fermentation under two cultivation modes by LEfSe (SBF vs. OBF; SMF vs. OMF; Kruskal-Wallis and rank test α < 0.05; LDA score > 2.00). S: rain-shelter mode, green color-coded; O: open-filed mode, red color-coded. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 4

Aromatic and organoleptic characteristics of wine samples from two cultivation modes. Cluster analysis of varietal aromas (a) and (b) fermentative aromas. c: MF% of aroma characteristics of wines. (d) PLS regression plots of correlation loadings between chemical and sensory data showing the 75% (inner) and 100% (outer) explained variance limit. S: wine samples from rain-shelter mode; O: wine samples from open-filed mode; *: 0.01 < p ≤ 0.05; **: 0.001 < p ≤ 0.01; ***: p ≤ 0.001.

Fig. 5

Correlation analysis between microbiota and differential metabolites. OPLS-DA screening of differential metabolites (a) and S-plot distribution of wine samples (b). RDA analysis for predicting fungal (c) and bacterial (d) genera associated with differential metabolites. Spearman correlation heatmap between dominant (e) fungal and (f) bacterial species and volatiles (Spearman correlation coefficient, ρ ≥ 0.7). The blue color indicates a varietal aroma. S: wine samples from rain-shelter mode; O: wine samples from open-filed mode; *: 0.01 < p ≤ 0.05; **: 0.001 < p ≤ 0.01. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 6

Direct effects of initial microbiota and microbial community succession in the fermentation on wine aroma profiles. Structural equation model (SEM) fitting of normalized total effects of rain-shelter (a) and open-field (b) cultivations on wine aromas. Measures of overall model fit under rain-shelter cultivation mode are as follows: GFI: 0.881, NFI: 0.976, CFI: 0.974, P_χ2: 0.269. Measures of overall model fit under open-field cultivation mode were as follows: GFI: 0.843, NFI: 0.995, CFI: 0.995, P_χ2: 0.397. PD: phylogenetic diversity of initial microbiota (grape juice). Shannon index of microbiota from grape juice to the end of fermentation as a measure of microbial succession. SEM showed the impact on initial microbial diversity, microbial succession and metabolic diversity (wine aromas). Significance is indicated by *: 0.01 < p ≤ 0.05; **: 0.001 < p ≤ 0.01; ***: p ≤ 0.001. Positive paths were shown in red, but negative paths were indicated in blue. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)