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The effect of salinity on taste and odor characteristics of Pacific oyster (Crassostrea gigas) during depuration was investigated in this study. In combination with free amino acids (FAAs), 5ʹ-nucleotides, and organic acids, electronic tongues were measured to evaluate the changes in taste-related compounds. Gas chromatography-ion mobility spectrometry (GC-IMS) and electronic nose were used to analyze the odor compounds of C. gigas at different depuration salinities. The results showed that bitter substances in C. gigas significantly decreased as salinity decreased. The equivalent umami concentration (EUC) was highest at a salinity of 29 g/L. The GC-IMS results were consistent with the electronic-nose test results. After low-salinity depuration, aldehyde and ketone levels were significantly reduced, and furan concentrations increased. In addition, multivariate analysis was used to determine the correlation between each component and flavor profile differences due to depuration at various salinities. Overall, salinity of 29 g/L could be optimal for oyster depuration.

• The changes of flavor in C. gigas during depuration were characterized. • The flavor of C. gigas improved after 48 h depuration. • Significant alterations in the metabolite level across various depuration periods. • The content of aldehydes, ketones, and alcohols was the lowest at 48 h depuration. The flavor of Pacific oyster (Crassostrea gigas) significantly changed during the depuration process. This work aimed to explore the mechanism of flavor changes during the 72 h depuration by metabolomics combined with gas chromatography-ion mobility spectrometry (GC-IMS). The metabolomics analysis indicated that carbohydrate metabolism was more affected in the early stage of depuration, including the citrate cycle, glyoxylae and dicarboxylate metabolism, etc. After 72 h depuration, it affected mainly the metabolism of global and overview maps and nucleoside metabolism, etc. The equivalent umami concentration (EUC) value was calculated and exhibited a gradual increase following a 48 h depuration. The GC–MS results revealed that the content of furans was the highest, and the content of aldehydes, ketones, and alcohols was the lowest after 48 h depuration, while the content of aldehydes, ketones, and alcohols increased after 72 h depuration. All these results suggested the depuration period was recommended to be controlled within 48 h. [ABSTRACT FROM AUTHOR]

Depuration is a vital stage to ensure the safety of oyster consumption, and salinity had a great impact on the environmental adaptability of oysters, but the underlying molecular mechanism was poorly understood during depuration stage. Here, Crassostrea gigas was depurated for 72 h at different salinity (26, 29, 32, 35, 38 g/L, corresponding to ±20%, ±10% salinity fluctuation away from oyster's production area) and then analyzed by using transcriptome, proteome, and metabolome combined with bioinformatics techniques. The transcriptome showed that the salinity stress led to 3185 differentially expressed genes and mainly enriched in amino acid metabolism, carbohydrate metabolism, lipid metabolism, etc. A total of 464 differentially expressed proteins were screened by the proteome, and the number of up-regulated expression proteins was less than the down-regulated, indicating that the salinity stress would affect the regulation of metabolism and immunity in oysters. 248 metabolites significantly changed in response to depuration salinity stress in oysters, including phosphate organic acids and their derivatives, lipids, etc. The results of integrated omics analysis indicated that the depuration salinity stress induced abnormal metabolism of the citrate cycle (TCA cycle), lipid metabolism, glycolysis, nucleotide metabolism, ribosome, ATP-binding cassette (ABC) transport pathway, etc. By contrast with Pro-depuration, more radical responses were observed in the S38 group. Based on the results, we suggested that the 10% salinity fluctuation was suitable for oyster depuration and the combination of multi-omics analysis could provide a new perspective for the analysis of the mechanism changes. • Multi-omics was applied to study depuration salinity effect on C. gigas. • 248 metabolites, 464 proteins, and 3185 genes were significantly altered. • More radical responses were observed in the S38 group. • 10% salinity fluctuation was suitable for oyster depuration. [ABSTRACT FROM AUTHOR]

• Proteomic analysis revealed differentiating proteins (DPs) in C. gigas. • Levels of DPs associated with glycolysis increased with salinity stress. • Levels of DPs associated with ECM-receptor interaction pathway increased. • Depuration in 38 g/L salinity was detrimental to oyster quality. • Depuration salinity fluctuation should be controlled within ± 10% of production area. Salinity stress during depuration of Pacific oysters (Crassostrea gigas) leads to degradation in quality; therefore, an understanding of the molecular mechanisms regulating dynamic changes during depuration is needed. Here, C. gigas was depurated for 72 h at salinities ranging from 26 to 38 g/L, a ± 10–20% fluctuation from that in the production area, and the gill proteomes were analyzed by sequential window acquisition of all theoretical fragment ion mass spectra (SWATH-MS). Of the 1218 proteins analyzed, 241 were differentiating proteins (DPs). Salinity stress led to increased levels of DPs associated with glycolysis and the extracellular matrix–receptor interaction pathway, and decreased levels of DPs associated with the citric acid cycle, lipid metabolism, genetic information processing, and cell transformation, especially in oysters exposed to 38 g/L salinity (+20%). Controlling salinity fluctuation within ± 10% of the production area during depuration was conducive to maintaining quality in C. gigas. [ABSTRACT FROM AUTHOR]