Abstract
To investigate the effects of spoilage bacteria on aquatic product quality and volatile organic compounds (VOCs) in hybrid grouper (Epinephelus fuscoguttatus ♀×Epinephelus lanceolatus ♂), the physical conditions were evaluated, the chemical changes including color, total volatile base nitrogen (TVB-N), VOCs, and free amino acids (FFAs) were determined, and biological profiles were made through microbial community (total viable counts (TVC), 16S rRNA gene amplification sequencing, and next-generation sequencing (NGS) technology on hybrid grouper, which were stored at 4 °C for 10 days. The results showed that the whiteness and TVB-N of grouper increased throughout the storage period. The contents of glycine, alanine, and total free amino acid decreased with the microbial activity towards the end of the study period. At the end of storage, the TVC reached 9.0 log10 (CFU/g). Seventy eight strains of bacteria were isolated from the hybrid grouper, most of which were shown to be Pseudomonas spp., after 16S rRNA sequencing. The results of the NGS test showed that the diversity of dominant bacteria decreased with time; Pseudomonas azotoformans was the dominant spoilage bacteria at the end of storage. The VOCs of fish and bacteria in the grouper’s spoilage process were presented in headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS). Twenty eight compounds were identified in hybrid grouper, among which alcohol and aldehyde were used to characterize freshness, both of which were not only related to the overall flavor of the grouper, but were also affected by microbial activity. However, due to the complexity of microbial communities in aquatic products, the correlation between community changes and VOCs needs further research. This study provides insights into the correlation between VOCs and specific spoilage organisms (SSOs) through the analysis of the microbial community and VOCs.
Highlights
Aquatic products are perishable due to biological and chemical changes
There was a fluctuation on day 6, which may be have been caused by external factors such as the size of the fish, heterogeneity, and the feeding ingredients of the batches of fish [17]
As shown in the figure, the group of Pseudomonas rhodesiae, Pseudomonas antarctica, Pseudomonas azotoformans, Pseudomonas koreensis, Pseudomonas moraviensis, and Pseudomonas extremaustralis were highly related to the production of pyrazines and hydrocarbons, while Macrococcus caseolyticus, Moraxella osloensis, Shewanella putrefaciens, Staphylococcus saprophyticus, Pseudomonas putida, and Pseudomonas helmanticensis were less related to these aromatic compounds. but produced higher levels of alcohol and other compounds
Summary
Aquatic products are perishable due to biological and chemical changes. Along with the quality deterioration caused by microbial growth, the odor and flavor of fish undergo great shifts that directly influence customers’ purchasing behavior [1]. Various microorganisms produce compounds with special odors such as nitrogenous compounds, aldehydes, ketones, and esters [2,3,4] They are primarily used to profile the composition of microbiota, and evaluate changes in quality and their relation with the quality and composition of microbiota during fish storage. The cause of off-flavors and organoleptic rejection of seafood are related to a consortium of the metabolites (chemical spoilage indices, CSIs) produced by bacteria called Specific Spoilage Organisms (SSOs) [2]. These metabolites include a range of volatile organic compounds (VOCs). The headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) is a useful analytical method for testing for VOCs, which can be used to identify potential strategies for quality assessments and for estimates of remaining shelf life [5,6,7,8,9]
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