Effects of substrates and suppliers of ingredients on microbial community and metabolites of traditional non-salt Suancai.

Aim: Non-salt Suancai is an acidic fermented vegetable consumed by the Chinese Yi ethnic group. Traditionally, it is produced by fermentation without salt in a cold environment. The present study aimed to investigate the metabolite and microbial characteristics, and the effects of substrates/suppliers ingredients on non-salt Suancai. Methods: A simulated fermentation system of non-salt Suancai was constructed by using different substrates/suppliers' ingredients. The coherence and differential detection of the metabolite and microbial characteristics were done through non-target metabolomic and metagenomic analysis. Results: Lactic acid was the predominant organic acid across all samples. The enumeration of the Lactic acid bacteria showed no discernible differences between study groups, but that of yeast was highest in the mustard leaf stem (Brassica juncea var. latipa). The three major biological metabolic pathways were metabolism, environmental information, and genetic information processing based on the KEGG database. The metabolite diversity varied with the substrate/supplier of ingredients based on the PLS-DA plot. Lactiplantibacillus, Leuconostoc, and Lactococcus 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.

Characterizing the impact of species/strain-specific Lactiplantibacillus plantarum with community assembly and metabolic regulation in pickled Suancai.

To investigate the colonization and impact of the specific Lactiplantibacillus plantarum strains, four isolated strains were applied in pickled Suancai which is a traditional pickled mustard (Brassica juncea). Results showed that strain-8 with the highest lactic acid bacteria (LAB) counts and acetic acid (p < 0.05). There were 11.42 % ∼ 32.35 % differential volatile compounds detected, although nitriles, esters, and acids were predominant. L. plantarum disturbed the microbial community, in which the microbial composition of strain-11 was most similar to the naturally fermented sample. Amino acids, carbohydrate metabolism, and metabolism of cofactors and vitamins were the main functional classes because of the similar dominant microbes (Lactiplantibacillus and Levilactobacillus). The functional units were separated based on NMDS analysis, in which bacterial chemotaxis, amino acid-related units, biotin metabolism, fatty acid biosynthesis, and citrate cycle were significantly different calculated by metagenomeSeq and Benjamin-Hochberg methods (p < 0.05). The contents of most flavor compounds were consistent with their corresponding enzymes. In particular, glucosinolates metabolites were different and significantly related to the myrosinase and metabolic preference of LAB. Therefore, this study revealed the impact mechanism of the specific L. plantarum strains and provided a perspective for developing microbial resources to improve the flavor diversity of fermented vegetables.

Comprehensive Profiling of Macamides and Fatty Acid Derivatives in Maca with Different Postharvest Drying Processes Using UPLC-QTOF-MS.

Macamides are characteristically found in maca (Lepidium meyenii Walper). Fatty acid derivatives are also an important type of constituent in maca, since they not only relate to the biosynthesis of macamides in the postharvest process but also possess some bioactivities. To study their comprehensive profiles in maca tubers processed via the air-drying method, ultraperformance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) analyses were performed to identify macamide and fatty acid molecules. Their contents in maca tubers that were processed via air drying and freeze drying, respectively, were further quantified using high-performance liquid chromatography (HPLC) analyses comparing with eight macamide and three fatty acid reference standards. A total of 19 macamides (including four novel ones) and 16 fatty acid derivatives (two found in maca for the first time) were identified. Quantification analyses results showed the eight macamides with contents ranging from 31.39 to 1163.19 µg/g (on dry tuber), and fatty acids from 18.71 to 181.99 µg/g in the air-dried maca, but there were only three macamides and one fatty acid detected with very low contents (3.97-34.36 µg/g) in the freeze-dried maca. The results demonstrated that the air-drying method can increase the accumulations of macamides and fatty acids in the metabolism of maca in the postharvest process. The biosynthesis of two types of macamides, i.e., N-benzyl-oxo-octadecadienamides and N-benzyl-oxo-octadecatrienamides, was further elucidated in detail. These results provide more valuable insights into the phytochemicals of maca, which is helpful to explain its health benefits.

Bacterial community succession and metabolite changes during doubanjiang-meju fermentation, a Chinese traditional fermented broad bean (Vicia faba L.) paste.

Doubanjiang-meju, a major ingredient of Chinese fermented food for several centuries, is produced using broad bean, wheat flour and salt. In this study, we investigated prokaryotic community succession and metabolite changes using high-throughput sequencing and 1H-NMR methods. After 35 days, bacterial communities, except Lactobacillus and Acinetobacter, were relatively stable until the end of fermentation, and consisted predominantly of the genera Tetragenococcus, Lactobacillus, Staphylococcus, Acinetobacter, Pseudomonas and Streptococcus. Glucose, arabinose, fructose and mannitol were identified as major sugars, lactate and acetate as major organic acids, and amino acids as the major nitrogen compounds present in doubanjiang-meju. Correlation analysis revealed important links between bacterial populations and metabolites, e.g., Pseudomonas was significantly correlated with 10 nitrogenous metabolites, while Streptococcus was significantly correlated with six carbonic metabolite and eight nitrogenous metabolites. These results not only revealed bacterial succession and dynamic changes in metabolites as well as pH and color, but also elucidated their relationships during the doubanjiang-meju fermentation.