The Fungal Communities and Flavor Profiles in Different Types of High-Temperature Daqu as Revealed by High-Throughput Sequencing and Electronic Senses

Abstract

Polymicrobial co-fermentation is among the distinct character of high-temperature Daqu. However, fungal communities in the three types of high-temperature Daqu, namely, white high-temperature Daqu, black high-temperature Daqu, and yellow high-temperature Daqu, are yet to be characterized. In this study, the fungal diversity, taste, and aroma profiles in the three types of high-temperature Daqu were investigated by Illumina MiSeq high-throughput sequencing, electronic tongue, and electronic nose, respectively. Ascomycota and Basidiomycota were detected as the absolute dominant fungal phylum in all types of high-temperature Daqu samples, whereas Thermomyces, Thermoascus, Aspergillus, Rasamsonia, Byssochlamys, and Trichomonascus were identified as the dominant fungal genera. The fungal communities of the three types of high-temperature Daqu differed significantly (p < 0.05), and Thermomyces, Thermoascus, and Monascus could serve as the biomarkers in white high-temperature Daqu, black high-temperature Daqu, and yellow high-temperature Daqu, respectively. The three types of high-temperature Daqu had an extremely significant difference (p < 0.01) in flavor: white high-temperature Daqu was characterized by sourness, bitterness, astringency, richness, methane, alcohols, ketones, nitrogen oxides, and sulfur organic compounds; black high-temperature Daqu was characterized by aftertaste-A, aftertaste-B, methane-aliph, hydrogen, and aromatic compounds; and yellow high-temperature Daqu was characterized by saltiness, umami, methane, alcohols, ketones, nitrogen oxides, and sulfur organic compounds. The fungal communities in the three types of high-temperature Daqu were significantly correlated with taste but not with aroma, and the aroma of high-temperature Daqu was mainly influenced by the dominant fungal genera including Trichomonascus, Aspergillus, Thermoascus, and Thermomyces. The result of the present study enriched and refined our knowledge of high-temperature Daqu, which had positive implications for the development of traditional brewing technique.

Keywords: Illumina MiSeq high-throughput sequencing; electronic nose; electronic tongue; fungal diversity; high-temperature Daqu; sauce-flavor Baijiu.

FIGURE 1

Boxplots of α-diversity indexes. (A) Number of observed species; (B) Shannon diversity index.

FIGURE 2

Fungal composition of HTD samples at the level of phylum (A) and genus (B).

FIGURE 3

Prevalence (A) and average relative abundance (B) of OTUs in HTD samples.

FIGURE 4

PCoA score plots based on Bray–Curtis distance (A); dendrogram based on Bray–Curtis distance calculated using Mahalanobis distances and MANOVA (B); within-group variations of the three types of HTD calculated on the basis of Bray–Curtis distance (C). Significant difference is represented by ^*** (0.0001 ≤ p < 0.001), ^** (0.001 ≤ p < 0.01), and ns (p ≥ 0.05), respectively. Identification of discriminant taxa among the three types of HTD by LEfSe: cladogram of the fungal communities (D). Horizontal bar chart showing discriminant taxa (E).

FIGURE 5

Box plot for taste profiles of the three types of HTD samples (A). Significant difference is represented by ^**** (p < 0.0001). PCA biplot based on the taste profiles of HTD samples (B). Procrustes analysis of the correlation between dominate fungal genera and aroma profiles (M² = 0.889, p = 0.079, 999 permutations) (C).

FIGURE 6

Box plot for aroma profiles of the three types of HTD samples (A). Significant difference is represented by ^**** (p < 0.0001), ^*** (0.0001 ≤ p < 0.001), and ^** (0.001 ≤ p < 0.01), respectively. PCA biplot based on the aroma profiles of HTD samples (B). Procrustes analysis of the correlation between dominate fungal genera and aroma profiles (M² = 0.828, p = 0.007, 999 permutations) (C). Heatmap depicting the Spearman’s rank correlation between dominant fungal genera and E-nose sensors. Significant difference is represented by * (p < 0.05) (D).