Comparison of the taste mechanisms of umami and bitter peptides from fermented mandarin fish (Chouguiyu) based on molecular docking and electronic tongue technology.

Unclear taste mechanisms of peptides limit rapid screening of taste peptides with high intensity. In this study, the taste mechanisms of umami and bitter peptides from Chouguiyu were compared. After molecular docking of core umami (NWDDMEK, WFKDEEF, EEEKPKF, DFDDIQK, and DGEKVDF) and bitter (VQDVLKL, VELLKLE, LVVDGVK, VVDLTVR, and VVDGVKL) peptides with T1R1/T1R3 and TASR14, respectively, salt bridges and conventional hydrogen bonds were the main interactions in all taste peptides, in which acidic amino acid residues contributed to the interaction with their receptors. The taste intensity of peptides after solid-phase synthesis was further verified using electronic tongue technology. Spearman correlation analysis showed that docking energy was an important factor for the intensity of taste peptides, while interaction energy and the distance between the binding unit (BU) and the stimulating unit (SU) were also responsible for the bitter intensity. This study provides a theoretical basis to screen novel taste peptides with high taste intensity in fermented foods.

Novel insight into flavor and quality formation in naturally fermented low-salt fish sauce based on microbial metabolism.

Low-salt fermentation is an effective way to shorten the fermentation time of fish sauce. In this study, the changes of microbial community, flavor, and quality during the natural fermentation of low-salt fish sauce were studied, followed by the elucidation of flavor and quality formation mechanisms based on microbial metabolism. The 16S rRNA gene high-throughput sequencing showed that both richness and evenness of microbial community were reduced during fermentation. The microbial genera, including Pseudomonas, Achromobacter, Stenotrophomonas, Rhodococcus, Brucella, and Tetragenococcus were more suitable for the fermentation environment, and obviously increased along with the fermentation. There were a total of 125 volatile substances identified by HS-SPME-GC-MS, of which 30 substances were selected as the characteristic volatile flavor substances, mainly including aldehydes, esters, and alcohols. Large amounts of free amino acids were produced in the low-salt fish sauce, especially umami and sweet amino acids, as well as high concentrations of biogenic amines. Correlation network constructed by the Pearson's correlation coefficient showed that most characteristic volatile flavor substances were significantly positively correlated with Stenotrophomonas, Achromobacter, Rhodococcus, Tetragenococcus, and Brucella. Stenotrophomonas and Tetragenococcus were significantly positively correlated with most free amino acids, especially umami and sweet amino acids. Pseudomonas and Stenotrophomonas were positively correlated with most biogenic amines, especially histamine, tyramine, putrescine, and cadaverine. Metabolism pathways suggested that the high concentrations of precursor amino acids contributed to the production of biogenic amines. This study indicates that the spoilage microorganisms and biogenic amines in the low-salt fish sauce need to be further controlled, and the strains belonging to Tetragenococcus can be isolated as potential microbial starters for the production of low-salt fish sauce.

Isolation and characterization of antioxidant peptides from oyster (Crassostrea rivularis) protein enzymatic hydrolysates.

Peptides from oysters have several bioactive functions. In this study, we identified antioxidant peptides from oysters (Crassostrea rivularis) and investigated their structure-function relationship. We used an 8 kDa molecular-weight (MW) cut-off membrane and semiprep reversed-phase liquid chromatography to collect five peptides (F1-F5) and identified the highest-abundance ion-peak sequences AWVDY (F1), MSFRFY(F2), EPLRY(F3), RKPPWPP(F4), and YAKRCFR(F5) having MWs of 652, 850, 676, 877, and 943 Da, respectively, using ultra-performance liquid chromatography-quadrupole/time-of-flight tandem mass spectrometry. These peptides exhibited high antioxidant activities, similar to butylated hydroxytoluene, reduced glutathione, and ascorbic acid. F5 demonstrated the highest scavenging activity for DPPH radicals (IC50 = 21.75 µg/ml), hydroxyl radicals (IC50 = 18.75 µg/ml), and superoxide radicals (IC50 = 11.00 µg/ml), while F3 demonstrated the highest reducing power. Furthermore, F5 significantly protected Caco-2 cells from H2O2-induced oxidative damage. These results suggest that the antioxidant peptide F5 is a promising food additive that protects against oxidative damage.

Discovery and functional mechanism of novel dipeptidyl peptidase â £ inhibitory peptides from Chinese traditional fermented fish (Chouguiyu).

Dipeptidyl peptidase-IV (DPP-IV) inhibitory peptides from fermented foods exhibit great potential to alleviate type 2 diabetes mellitus (T2DM). In this study, the DPP-IV inhibition activity of peptide extract from Chouguiyu was obviously enhanced after 4-8 d fermentation. A total of 125 DPP-IV inhibitory peptides in Chouguiyu were identified by peptidomics and were obtained from 46 precursor proteins, mainly including nebulin, titin, muscle-type creatine kinase, hemoglobin, and actin. After molecular docking with DPP-IV, four novel DPP-IV inhibitory peptides possessing the lowest docking energy were selected, including EPAEAVGDWR (D37), IPHESVDVIK (D22), PDLSKHNNHM (D35), and PFGNTHNNFK (D1). The DPP-IV inhibition activity of D37, D22, D35, and D1 were further verified after synthesis with the IC50 of 0.10 mM, 2.69 mM, 3.88 mM, and 8.51 mM, respectively, in accordance with their docking energies. Energy interaction showed that the structures of EP-, IPH-, -NHM, and PF- in these peptides were easy to connect with DPP-IV enzyme through hydrogen bond, salt bridge, and alkyl. The surface force including the H-bond interaction, hydrophobicity, aromatic interaction, and SAS, played a major role in the interaction between DPP-IV enzyme and peptides. The peptides that possess high hydrophobicity and can form strong hydrogen bond and salt bridge are potential DPP-IV inhibitory peptides using for T2DM remission.

Formation and inhibition mechanism of novel angiotensin I converting enzyme inhibitory peptides from Chouguiyu.

Angiotensin I converting enzyme (ACE) inhibitory peptides from fermented foods exhibit great potential to alleviate hypertension. In this study, the peptide extract from Chouguiyu exhibited a good inhibition effect on ACE, and the inhibition rate was significantly enhanced after fermentation for 8 days. The ACE inhibitory peptides were further identified, followed by their inhibition and formation mechanisms using microbiome technology and molecular docking. A total of 356 ACE inhibitory peptides were predicted using in silico, and most ACE inhibitory peptides increased after fermentation. These peptides could be hydrolyzed from 94 kinds of precursor proteins, mainly including muscle-type creatine kinase, nebulin, and troponin I. P1 (VEIINARA), P2 (FAVMVKG), P4 (EITWSDDKK), P7 (DFDDIQK), P8 (IGDDPKF), P9 (INDDPKIL), and P10 (GVDNPGHPFI) were selected as the core ACE inhibitory peptides according to their abundance and docking energy. The salt bridge and conventional hydrogen bond connecting unsaturated oxygen atoms in the peptides contributed most to the ACE inhibition. The cleavage proteases from the microbial genera in Chouguiyu for preparing these 7 core ACE inhibitory peptides were further analyzed by hydrolysis prediction and Pearson's correlation. The correlation network showed that P7, P8, and P9 were mainly produced by the proteases from LAB including Lactococcus, Enterococcus, Vagococcus, Peptostreptococcus, and Streptococcus, while P1, P2, P4, and P10 were mainly Produced by Aeromonas, Bacillus, Escherichia, and Psychrobacter. This study is helpful in isolating the proteases and microbial strains to directionally produce the responding ACE inhibitory peptides.

Novel insight into the formation mechanism of umami peptides based on microbial metabolism in Chouguiyu, a traditional Chinese fermented fish.

Umami peptides formed by microbial metabolism play an important role in the umami taste of Chouguiyu. In this study, 138 umami peptides and 6 kinds of proteases in two categories from 35 microbial genera were identified from Chouguiyu during the fermentation process by peptidomics and metagenomics analysis, respectively. The interaction network maps between the umami peptides and protease-producing microbial genera in each protease classification were constructed based on Pearson's correlation coefficient after a two-way orthogonal partial least squares (O2PLS) evaluation. The proteases classified in 34 clusters of orthologous groups (COG) from Vagococcus, Peptostreptococcus, Acinetobacter, Psychrobacter, and Enterococcus played a major role in the formation of umami peptides. The core umami peptides with the highest abundance and correlation were mainly derived from troponin and myosin in mandarin fish. The lactic acid bacteria contributed most to the hydrolysis preparation of these umami peptides. This study is beneficial to screen the proteases and related microbial strains to improve the umami taste of Chouguiyu.

Taste mechanism of umami peptides from Chinese traditional fermented fish (Chouguiyu) based on molecular docking using umami receptor T1R1/T1R3.

Umami peptides formed during fermentation of Chouguiyu contribute to its unique taste. In this study, the umami taste of peptide extract from Chouguiyu was improved after fermentation, as determined by sensory evaluation. After umami peptide identification using peptidomics, molecular docking with T1R1/T1R3 was used to evaluate the likely taste mechanism. There were 400 umami peptides identified in Chouguiyu, most of which were significantly enhanced after fermentation. These peptides were hydrolyzed from 77 precursor proteins, mainly including myosin, troponin, and titin, at multiple locations. The umami structures in the six core umami peptides with the lowest binding energy were easy to connect with Ser, Glu, His, Gln, Arg and Lys residues in T1R3 through hydrogen bond and salt bridge. The hydrogen bond, hydrophilcity, aromatic interaction, and solvent accessible surface were the main interaction surface forces. This study provides important information of the unique taste formation in Chouguiyu based on umami peptides.

Novel insight into the formation mechanism of volatile flavor in Chinese fish sauce (Yu-lu) based on molecular sensory and metagenomics analyses.

Complex microbial metabolism is the basis for flavor formation in traditional fish sauce. To guide the targeted regulation of production quality, we used molecular sensory and metagenomics analyses to determine dynamic changes in volatile flavor compounds and microbial communities of fish sauce as fermentation progressed. In total, 56 volatile compounds were identified; of these, 3-methylthiopropanal had the highest average odor activity value. Twelve volatile compounds, key for fish sauce flavor development, were identified. Bidirectional orthogonal partial least squares analysis was applied to investigate the correlation between microorganisms and flavor substances. Five microbial genera including Halanaerobium, Halomonas, Tetragenococcus, Halococcus and Candidatus Frackibacter constituted the core microbial flora responsible for flavor formation. The microbial metabolic pathways degraded raw materials into primary metabolites, such as glucose, amino acids, and fatty acids. This study provides novel insights into the flavor formation mechanism of traditional fish sauce fermentation.

Application of UHPLC-Q/TOF-MS-based metabolomics in the evaluation of metabolites and taste quality of Chinese fish sauce (Yu-lu) during fermentation.

Spontaneous fermentation is a critical step in the processing of high-quality fish sauce. In this study, a comparative UHPLC-Q/TOF-MS-based metabolomics approach combining equivalent-quantification and the taste activity value (TAV) was used, for the first time, to evaluate the taste qualities and characterize metabolite profiles in Chinese fish sauce during fermentation. A total of 22,816 metabolite ion features were extracted from fish sauce samples. Forty-six metabolites, including amino acids, small peptides, organic acids, amines, carbohydrates, and nucleic acids, were identified as key chemical components of fish sauce. In addition, absolute quantification and TAV showed that aspartic acid and glutamic acid exert an important influence on the umami taste of fish sauce. Specific metabolites were primarily associated with amino acid metabolism, particularly alterations in arginine and proline metabolism. This study identifies chemical components and provides novel insights into the taste quality of fish sauce due to fermentation.