Using GC-IMS and SPME-GC-MS to Analysis the Flavor Improvement of Oyster (Crassostrea gigas) Hydrolysates Treated with Lemon Juice

Objects: The aim of this study was to find out the effect of lemon juice on the inhibition of lipid oxidation in oyster and flavor improvement of oyster hydrolysates. Furthermore, the difference of characteristic aromatic compounds in oyster hydrolysate before and after flavor improvement was clearly elucidated. Methods: The lemon juice was added to participate to the oyster (Crassostrea gigas) hydrolysis process to ameliorate the unpleasant odor of the hydrolysates. The volatile components in oyster hydrolysate before and after flavor improvement were analyzed by sensory evaluation, gas chromatography ion mobility spectrometry (GC-IMS), solid phase micro-extraction gas chromatograph mass spectrometer (SPME-GC-MS), and the characteristic aroma of oyster hydrolysate was analyzed by combining sensory threshold and ROAV (relative odor activity value) method. Results: The results showed that 40 kinds of volatile flavor compounds were identified in oyster samples with different treatment methods by GC-IMS. Seven new volatile flavor compounds with pleasent, fragrant, fruity characteristics were increased such as pinene, benzyl alcohol, linalool oxide, dodecanal, 2-methoxyphenol, 2-heptanone and butyl acetate. In contrast, six volatile flavor compounds with fishy and unpleasent characteristics were reduced such as (E,E)-2,4-octadienal, heptanal, nonanal, (E)-2-octenal, octanal and 1-octen-3-ol. The results of SPME-GC-MS analysis and ROAV showed that the amount of olefins were increased from 8.37% to 42.84%. The major volatile components of lemon such as D-limonene and β-Myrcene were detected in oyster protein hydrolysates with adding lemon juice. In addition, the results showed that, lemon juice had positive effect on oyster hydrolysates flavor, 1-octen-3-ol was not a key flavor compound (ROAV≥1) and the ROAV value of volatile flavor compounds with fishy and unpleasent smell such as heptanal and (E)-2-octenal were decreased, and the overall bad flavor weakened. Conclusion: Lemon juice participating in the hydrolysis process of oyster can effectively reduce the fishy and unpleasent smell of oyster hydrolysate. This method is efficient, convenient and safe. This study can provide valuable reference for expanding the application of oyster hydrolysate and promoting the development of industrial deodorization technology.