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Page 2 of 15 Lai et al. Microbiome Res Rep 2024;3:21 https://dx.doi.org/10.20517/mrr.2023.76

were prevalent in all samples but differentially. The microbial diversity and richness varied significantly, with
36~291 species being identified. Among the various substrates collected from the same supplier, 29, 59, and 29
differential species were identified based on LEfSe [linear discriminant analysis (LDA) > 2, P < 0.05]. Leuconostoc
citreum, Leuconostoc mesenteroides, Leuconostoc pseudomesenteroides, Lactiplantibacillus plantarum, and Leuconostoc
lactis were likely to be used as the species to discriminate samples collected from different suppliers.

Conclusions: This research contributed to the exploration of microbial and metabolite characteristics behind the
ingredient restriction of non-salt Suancai using traditional technology.

Keywords: Non-salt Suancai, substrate/supplier of ingredients, metabolites, microbial community

INTRODUCTION
Non-salt Suancai is a traditional fermented vegetable (Brassica L.), which is widely consumed in the
southwest of Sichuan Province (the Yi ethnic group), China for its acidic taste. In contrast to most Suancai
consumed in other regions, non-salt Suancai can be rapidly fermented without salt and naturally air-dried
in winter (8 °C ~ 16 °C). The key method for fermentation of Suancai is the boiling of raw materials
followed by the addition of fermentation starter (preserved dried Suancai) [Supplementary Figure 1].
Thermally treated root vegetables enhance the release of polysaccharides, especially that of β-glucans and
pectic components, and increase the viscosity . Starter culture is a frequently used technique to control and
[1]
[2]
improve the quality of fermented products . Thus, the typical way of using preserved dried Suancai as a
fermentation starter is an effective method to supply complex and naturally selected microbiota. These
microbiota can accelerate the fermentation process and regulate the quality of the product . This technique
[3]
of producing non-salt Suancai gives it a distinctive feature with a strong sour fragrance and a sliding-back
sweet taste. However, the quality characteristics of non-salt Suancai with the special processing technology
are still to be explored.

Fermentation represents complex high-order microbial interactions. Notably, the microbial terroir of grapes
has been linked to its origin, which also determines the regional variation of wine . This concept also aligns
[4]
with the research on Daqu, a traditional Chinese liquor fermentation starter, which contains abundant
[5]
microbiota that contribute to its metabolite profile . A significant amount of evidence suggests that terroir
[6]
influences metabolites, microbes, and sensory characteristics in kimchi, a Korean vegetable product .
Therefore, the microbial terroir of preserved dried Suancai varies with different suppliers due to natural
fermentation. The investigation of the microbial characteristics of non-salt Suancai produced by different
suppliers is crucial to understanding the mechanism behind this fermentation method. The variety of active
ingredients is also a critical factor that influences the quality of the fermented product. The inherent
attributes and the recognizable strains differ with the substrate of ingredients, and the difference in
[7]
[8]
substrates further alters the quality of fermented products. For example, metagenomic analysis reveals that
differences in amino acid and carbohydrate metabolism pathways between sorghum substrates alter the
volatility of Chinese strong-flavored Baijiu . Similarly, within fermented vegetables, the substrate of garlic
[9]
influences the microbial ecology and metabolite profile of kimchi , and the selection of chili pepper had a
[10]
significant effect on the physiochemical property and the flavor of Paojiao, a fermented Chinese chili
pepper . However, there is a lack of knowledge regarding the effects of different substrates/supplier
[11]
patterns on non-salt Suancai.

Metabolomics involves comprehensive identification and quantification of small molecules (≤ 1,500 Da).
When typically coupled with nuclear magnetic resonance (NMR) or mass spectrometry (MS) with upstream
separation methods, it can improve the understanding of the quality attribute of foods at the molecular