Fermentation is an important process that can provide new flavors and nutritional and functional foods, to deal with changing consumer preferences. Fermented foods have complex chemical components that can modulate unique qualitative properties. Consequently, monitoring the small molecular metabolites in fermented food is critical to clarify its qualitative properties and help deliver personalized nutrition. In recent years, the application of metabolomics to nutrition research of fermented foods has expanded. In this review, we examine the application of metabolomics technologies in food, with a primary focus on the different analytical approaches suitable for food metabolomics and discuss the advantages and disadvantages of these approaches. In addition, we summarize emerging studies applying metabolomics in the comprehensive analysis of the flavor, nutrition, function, and safety of fermented foods, as well as emphasize the applicability of metabolomics in characterizing the qualitative properties of fermented foods.

Metabolomics Approaches for the Comprehensive Evaluation of Fermented Foods: A Review

Flavor characteristics of raw shrimp, high-salt and low-salt shrimp paste were evaluated and compared by sensory analysis, headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS) and solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS). In addition, aroma profiles and aroma-active compounds in these three samples were analyzed by solvent-assisted flavor evaporation-gas chromatography-olfactometry-mass spectrometry (SAFE-GC-O-MS). Results of sensory evaluation revealed that these three samples showed significant differences in sensitivity to the W2W, W2S, W1S and W1W sensors of the electronic nose (p < 0.05), which represent organic sulfides, alkane aromatic compounds, short chain alkanes, and sulfides, respectively. Assessment of sensory parameters indicated tha high-salt shrimp paste had a strong roasted and meaty aroma, while low-salt shrimp paste showed an umami aroma more similar to raw shrimp. A total of 118 volatile compounds were identified using the three afore-mentioned gas chromatography methods. Among them, 37 aroma-active compounds were detected by GC-O. High-salt shrimp was shown to contain more acids, aldehydes and heterocyclic compounds, which resembled cheese, roasted and meaty aromas. In contrast, low-salt shrimp paste contained more esters, which was similar to the umami aroma profile of raw shrimp. Interestingly, pyrazines were only produced in fermented shrimp paste samples, suggesting that they were produced during the fermentation process and they may contribute unique roasted and meaty aromas, which were important for the overall aroma characteristics of shrimp paste. 

Characterization of aroma profiles and aroma-active compounds in high-salt and low-salt shrimp paste by molecular sensory science

Flavor characteristics of raw shrimp, high-salt and low-salt shrimp paste were evaluated and compared by sensory analysis, headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS) and solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS). In addition, aroma profiles and aroma-active compounds in these three samples were analyzed by solvent-assisted flavor evaporation-gas chromatography-olfactometry-mass spectrometry (SAFE-GC-O-MS). Results of sensory evaluation revealed that these three samples showed significant differences in sensitivity to the W2W, W2S, W1S and W1W sensors of the electronic nose (p

Multi-omics revealed the formation mechanism of flavor in salted egg yolk induced by the stages of lipid oxidation during salting.

Halophilic bacteria as starter cultures: A new strategy to accelerate fermentation and enhance flavor of shrimp paste.

Shrimp paste is a traditional Chinese fermented food. To understand the relationship between microbial composition and flavor formation during the fermentation process, high-throughput sequencing and solid phase microextraction-gas chromatography technology were used to measure the dynamic changes of microbial communities and flavor composition. The bidirectional orthogonal partial least squares model was used to establish the correlation between volatile components and bacterial composition. A higher relative abundance of dominant genera including Salimicrobium, Lentibacillus, Lactobacillus, and Tetragenococcus was found throughout the fermentation period. Totally, 77 types of volatile compounds were detected, including nitrogen-containing compounds, aldehydes, alcohols, esters, and ketones. Alcohols (1-octanol, phenylethyl alcohol, and 2-butyl-1-octanol) and nitrogen-containing compounds (3-methyl-pyrazine and 2,5-dimethyl pyrazine) showed a positive correlation with Salimicrobium, Tetragenococcus, and Lactobacillus. Some aldehydes (isovaleraldehyde and 3-methylbutanal), ketones and nitrogenous compounds (trimethylamine and oxazole) were strongly negatively correlated with Lactobacillus, Salimicrobium, and Tetragenococcus. A correlation was established between the important microbes and the main flavor compounds. These results may provide a basis for the quality control and flavor compounds change mechanisms in the fermentation process of shrimp paste, which may be helpful to formulate standardized parameters and obtain constant quality products.

Bacterial composition changes and volatile compounds during the fermentation of shrimp paste: Dynamic changes of microbial communities and flavor composition

As an environmentally friendly and efficient method, successive two-step fermentation has been applied for extracting chitin from shrimp shells. To screen out the microorganisms for fermentation, a protease-producing strain, Exiguobacterium profundum, and a lactic acid-producing strain, Lactobacillus acidophilus, were isolated from the traditional fermented shrimp paste. Chitin was extracted by successive two-step fermentation with these two strains, and 85.9 ± 1.2% of protein and 95 ± 3% of minerals were removed. The recovery and yield of chitin were 47.82 and 16.32%, respectively. Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy (SEM) were used to characterize the chitin. The crystallinity index was 54.37%, and the degree of deacetylation was 3.67%, which was lower than that of chitin extracted by the chemical method. These results indicated that successive two-step fermentation using these two bacterial strains could be applied to extract chitin. This work provides a suitable strategy for developing an effective method to extract chitin by microbial fermentation.

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Extraction of Chitin From Shrimp Shell by Successive Two-Step Fermentation of Exiguobacterium profundum and Lactobacillus acidophilus.

The objective of this study was to investigate the effects of halophilic bacteria, including Virgibacillus sp. ZV10-1, Virgibacillus sp. SK37, and Staphylococcus nepalensis JS11 as starters on physicochemical, sensory, and taste properties of rapidly-fermented shrimp paste. Halophilic bacteria reduced moisture and total volatile basic nitrogen content and increased the pH and amino acid nitrogen content of shrimp pastes. Higher levels of total organic acids (484.47 ± 10.40 mg/100 g) were detected in sample inoculated with S. nepalensis JS11. Assessment of sensory parameters indicated that the three-bacteria compound inoculation group improved taste of shrimp paste effectively and contained the highest level of free amino acids (8930.25 ± 3.51 mg/100 g) and equivalent umami concentration (EUC) (960.32 g MSG/100 g). Furthermore, partial least squares regression analysis demonstrated that rapidly-fermented shrimp pastes were associated with sweetness, umami, color, texture, and overall liking attributes, which were related to the presence of tartaric acid, malic acid, GMP, Glu, Asp, Arg and Thr. Thus, this study highlights the potential of Virgibacillus sp. SK37 and S. nepalensis JS11 for the production of rapidly-fermented shrimp paste with improved taste profiles.

Jing Yu

Papers

Bacterial composition changes and volatile compounds during the fermentation of shrimp paste: Dynamic changes of microbial communities and flavor composition

Characterization of aroma profiles and aroma-active compounds in high-salt and low-salt shrimp paste by molecular sensory science

Extraction of Chitin From Shrimp Shell by Successive Two-Step Fermentation of Exiguobacterium profundum and Lactobacillus acidophilus.

Halophilic bacteria as starter cultures: A new strategy to accelerate fermentation and enhance flavor of shrimp paste.

Virgibacillus sp. SK37 and Staphylococcus nepalensis JS11 as potential starters to improve taste of shrimp paste