Mass spectrometry based metabolomics approach on the elucidation of volatile metabolites formation in fermented foods: A mini review

UHPLC-HRMS based saponins profiling of three morphological regions in American ginseng (Panax quinquefolium L.) and their correlation with the antioxidant activity

American ginseng (Panax quinquefolium L.) is used as tonic plant and high-grade nourishment. Ultra-high-performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS) method was established for identifying the chemical constituent in three morphological regions of American ginseng, including main root (MR), rhizome (RH) and lateral root (LR). The 63 saponins was identified in different morphological regions of 10 American ginseng samples. The chemical maker compounds in corresponding morphological region, while the major compounds of MR (malonyl-ginsenoside Rb1, ginsenoside Rd, Rs2 and pseudo-RC1), LR (stipuleanoside R2, ginsenoside Re and malonyl-ginsenoside Rc), and RH (malonyl-ginsenoside Rd, Rb3, and chikusetsu saponin II) were discovered. Correlation analysis showed that 11 compounds were positively correlated with the antioxidant activity of American ginseng.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-023-01453-4.

Our extended microbiome: The human-relevant metabolites and biology of fermented foods

One of the key modes of microbial metabolism occurring in the gut microbiome is fermentation. This energy-yielding process transforms common macromolecules like polysaccharides and amino acids into a wide variety of chemicals, many of which are relevant to microbe-microbe and microbe-host interactions. Analogous transformations occur during the production of fermented foods, resulting in an abundance of bioactive metabolites. In foods, the products of fermentation can influence food safety and preservation, nutrient availability, and palatability and, once consumed, may impact immune and metabolic status, disease expression, and severity. Human signaling pathways perceive and respond to many of the currently known fermented food metabolites, though expansive chemical novelty remains to be defined. Here we discuss several aspects of fermented food-associated microbes and metabolites, including a condensed history, current understanding of their interactions with hosts and host-resident microbes, connections with commercial probiotics, and opportunities for future research on human health and disease and food sustainability.

Aroma correlation assisted volatilome coupled network analysis strategy to unveil main aroma-active volatiles of Rosa roxburghii

To investigate the main aroma-active volatiles out from comprehensive chemical profile, we proposed an aroma correlation assisted volatilome coupled network analysis strategy and applied it to the study of Rosa roxburghii. Based on 475 detected volatiles with GC × GC-TOF/MS analysis, the volatilome was screened with both positive aroma activities and high contents to discover some aliphatic acids, alcohols, aldehydes and esters, terpenoids as well as some alkenes and ketones. Especially, a series of homologous C6- and C8- acids, alcohols, aldehydes, esters as well as some terpenoids like limonene take the predominant contributions to the aromas. Moreover, two aroma-active and aroma-contributing volatile groups including acid-aldehyde-alcohol-ester and terpenoid groups were clustered to integrally be responsible for the major aromas of R. roxburghii with network analysis. Additionally, the accumulation of C6- and C8-family homologous aliphatic volatiles was also elucidated with linoleic and linolenic acid derived pathways. This strategy is practical to investigate the main aroma-active volatiles based on volatilome.

Applications of multi-omics techniques to unravel the fermentation process and the flavor formation mechanism in fermented foods

Fermented foods are important components of the human diet. There is increasing awareness of abundant nutritional and functional properties present in fermented foods that arise from the transformation of substrates by microbial communities. Thus, it is significant to unravel the microbial communities and mechanisms of characteristic flavor formation occurring during fermentation. There has been rapid development of high-throughput and other omics technologies, such as metaproteomics and metabolomics, and as a result, there is growing recognition of the importance of integrating these approaches. The successful applications of multi-omics approaches and bioinformatics analyses have provided a solid foundation for exploring the fermentation process. Compared with single-omics, multi-omics analyses more accurately delineate microbial and molecular features, thus they are more apt to reveal the mechanisms of fermentation. This review introduces fermented foods and an overview of single-omics technologies - including metagenomics, metatranscriptomics, metaproteomics, and metabolomics. We also discuss integrated multi-omics and bioinformatic analyses and their role in recent research progress related to fermented foods, as well as summarize the main potential pathways involved in certain fermented foods. In the future, multilayered analyses of multi-omics data should be conducted to enable better understanding of flavor formation mechanisms in fermented foods.

Integrated volatolomics and metabolomics analysis reveals the characteristic flavor formation in Chouguiyu, a traditional fermented mandarin fish of China

Volatolomics and metabolomics were performed to explore the generation mechanism of the characteristic flavor of mandarin fish during fermentation. This study revealed a novel finding that umami-tasting amino acids, succinic acid, and peptides increased, while taste-presenting nucleotides decreased after fermentation. The results showed that 19 key aroma compounds were identified. The most nitrogenous compounds were produced after fermentation, the total concentration of which was >5 mg/kg. A high odor activity value of 443 was established for stinky indole. PLS-DA showed that sn-glycero-3-phosphocholine, hypoxanthine, creatine, and trimethylamine N-oxide were the key metabolites associated with the key volatiles. Umami-tasting amino acids could contribute to the characteristic taste. Metabolic pathway analysis revealed that tryptophan metabolism, trimethylamine metabolism, and monoterpenoid biosynthesis were the potential generation pathways of indole, trimethylamine, and terpenoids, respectively. Collectively, the results provide thoughts for targeted controlling the flavor of fermented mandarin fish.

Advances in microbial analysis: based on volatile organic compounds of microorganisms in food

In recent years, microbial volatile organic compounds (mVOCs) produced by microbial metabolism have attracted more and more attention because they can be used to detect food early contamination and flaws. So far, many analytical methods have been reported for the determination of mVOCs in food, but few integrated review articles discussing these methods are published. Consequently, mVOCs as indicators of food microbiological contamination and their generation mechanism including carbohydrate, amino acid, and fatty acid metabolism are introduced. Meanwhile, a detailed summary of the mVOCs sampling methods such as headspace, purge trap, solid phase microextraction, and needle trap is presented, and a systematic and critical review of the analytical methods (ion mobility spectrometry, electronic nose, biosensor, and so on) of mVOCs and their application in the detection of food microbial contamination is highlighted. Finally, the future concepts that can help improve the detection of food mVOCs are prospected.

Microbial foods for improving human and planetary health

The current food production system is negatively impacting planetary and human health. A transition to a sustainable and fair food system is urgently needed. Microorganisms are likely enablers of this process, as they can produce delicious and healthy microbial foods with low environmental footprints. We review traditional and current approaches to microbial foods, such as fermented foods, microbial biomass, and food ingredients derived from microbial fermentations. We discuss how future advances in science-driven fermentation, synthetic biology, and sustainable feedstocks enable a new generation of microbial foods, potentially impacting the sustainability, resilience, and health effects of our food system.

Highlighting the Impact of Lactic-Acid-Bacteria-Derived Flavours or Aromas on Sensory Perception of African Fermented Cereals

Sensory characteristics and flavour profiles of lactic-acid-fermented foods are influenced by lactic acid bacteria (LAB) metabolic activities. The flavour compounds released/produced are directly linked to the sensory characteristics of fermented cereals. African fermented cereals constitute a staple, frequently consumed food group and provide high energy and essential nutrients to many communities on the continent. The flavour and aroma characteristics of fermented cereal products could be correlated with the metabolic pathways of fermenting microorganisms. This report looks at the comprehensive link between LAB-produced flavour metabolites and sensory attributes of African fermented cereals by reviewing previous studies. The evaluation of such data may point to future prospects in the application of flavour compounds derived from African fermented cereals in various food systems and contribute toward the improvement of flavour attributes in existing African fermented cereal products.

Evaluating the effect of lactic acid bacteria fermentation on quality, aroma, and metabolites of chickpea milk

Legumes are an attractive choice for developing new products since their health benefits. Fermentation can effectively improve the quality of soymilk. This study evaluated the impact of Lactobacillus plantarum fermentation on the physicochemical parameters, vitamins, organic acids, aroma substances, and metabolites of chickpea milk. The lactic acid bacteria (LAB) fermentation improved the color, antioxidant properties, total phenolic content, total flavonoid content, lactic acid content, and vitamin B6 content of raw juice. In total, 77 aroma substances were identified in chickpea milk by headspace solid-phase microextraction with gas chromatography/mass spectrometry (HS-SPME-GC-MS); 43 of the 77 aroma substances increased after the LAB fermentation with a significant decrease in beany flavor content (p < 0.05), improving the flavor of the soymilk product. Also, a total of 218 metabolites were determined in chickpea milk using non-targeted metabolomics techniques, including 51 differentially metabolites (28 up-regulated and 23 down-regulated; p < 0.05). These metabolites participated in multiple metabolic pathways during the LAB fermentation, ultimately improving the functional and antioxidant properties of fermented soymilk. Overall, LAB fermentation can improve the flavor, nutritional, and functional value of chickpea milk accelerating its consumer acceptance and development as an animal milk alternative.

Metagenomic-Metabolomic Mining of Kinema, a Naturally Fermented Soybean Food of the Eastern Himalayas

Kinema is a popular sticky fermented soybean food of the Eastern Himalayan regions of North East India, east Nepal, and south Bhutan. We hypothesized that some dominant bacteria in kinema may contribute to the formation of targeted and non-targeted metabolites for health benefits; hence, we studied the microbiome-metabolite mining of kinema. A total of 1,394,094,912 bp with an average of 464,698,304 ± 120,720,392 bp was generated from kinema metagenome, which resulted in the identification of 47 phyla, 331 families, 709 genera, and 1,560 species. Bacteria (97.78%) were the most abundant domain with the remaining domains of viruses, eukaryote, and archaea. Firmicutes (93.36%) was the most abundant phylum with 280 species of Bacillus, among which Bacillus subtilis was the most dominant species in kinema followed by B. glycinifermentans, B. cereus, B. licheniformis, B. thermoamylovorans, B. coagulans, B. circulans, B. paralicheniformis, and Brevibacillus borstelensis. Predictive metabolic pathways revealed the abundance of genes associated with metabolism (60.66%), resulting in 216 sub-pathways. A total of 361 metabolites were identified by metabolomic analysis (liquid chromatography-mass spectrophotometry, LC-MS). The presence of metabolites, such as chrysin, swainsonine, and 3-hydroxy-L-kynurenine (anticancer activity) and benzimidazole (antimicrobial, anticancer, and anti-HIV activities), and compounds with immunomodulatory effects in kinema supports its therapeutic potential. The correlation between the abundant species of Bacillus and primary and secondary metabolites was constructed with a bivariate result. This study proves that Bacillus spp. contribute to the formation of many targeted and untargeted metabolites in kinema for health-promoting benefits.

Effects of pH and Osmotic Changes on the Metabolic Expressions of Bacillus subtilis Strain 168 in Metabolite Pathways including Leucine Metabolism

Bacillus subtilis is often exposed to diverse culture conditions with the aim of improving hygiene or food quality. This can lead to changes in the volatile metabolite profiles related to the quality of fermented foods. To comprehensively interpret the associated metabolic expressions, changes in intracellular primary and extracellular secondary volatile metabolites were investigated by exposing B. subtilis to an alkaline pH (BP, pH 8.0) and a high salt concentration (BS, 1 M). In particular, B. subtilis was cultured in a leucine-enriched medium to investigate the formation of leucine-derived volatile metabolites. This study observed metabolic changes in several metabolic pathways, including carbohydrate metabolism, amino acid metabolism, fatty acid metabolism, and leucine degradation. The formation of proline (an osmolyte), furans, pyrrole, and monosaccharide sugars (glucose, galactose, and fructose) was enhanced in BS, whereas fatty acid derivatives (ketones and alcohols) increased in BP. In the case of leucine degradation, 3-methyl-butanal and 3-methylbutanol could be salt-specific metabolites, while the contents of 3-methylbutanoic acid and 3-methylbutylacetate increased in BP. These results show culture condition-specific metabolic changes, especially secondary volatile metabolites related to the sensory property of foods, in B. subtilis.