Integrated volatile compounds and non-targeted metabolomics analysis reveal the characteristic flavor formation of proteins in grouper (Epinephelus coioides) during cold storage

Microorganisms, lipids, and proteins always interact in a complex way in the fish matrix, which becomes a hindrance to evaluate the quality of the individual factors affecting them. In order to investigate the relationship between protein deterioration and volatile compounds (VOCs) in grouper during cold storage, the myofibril protein (MP) was used as a single-factor study to exclude microorganisms and lipids effects. The oxidation and degradation of MP during storage at 4 ℃ were evaluated, including MP content, total sulfhydryl content, carbonyl content, spatial structure and microstructure. Headspace-solid phase microextraction- gas chromatography-mass spectrometry (HS-SPME-GC-MS) was used to analyze the VOCs of grouper MP, and a total of 7 key VOCs were selected, including three ketones (2-nonanone, 2-undecanone and 2-tridecanone), three esters (methyl butyrate, methyl palmitate and methyl ester 9-octadecenoic acid) and one alcohol (3-methyl-1-butanol). At the same time, a non-targeted metabolomics method based on UPLC-Q-Extractive Orbitrap was used to investigate the changes in metabolites during MP storage. A total of 107 up-regulated differential metabolites and 7 down-regulated metabolites were annotated, and 6 metabolic pathways highly related to proteins were screened. Spearman correlation analysis showed that 7 key VOCs are associated with the biosynthesis and metabolism of ornithine and lysine. And a possible solution to protein deterioration in grouper was proposed, which provided a reference for improving protein quality and regulating flavor formation during cold storage of grouper at source.