Volatiles Compounds Suitable of Rapid Detection as Quality Indicators of Aerobically Stored Fresh Salmon

Introduction: Spoilage is a process, in which food deteriorates to the point, when the quality of the product is unacceptable for consumers due to the microbiological, chemical or physical changes. The activity of microorganisms leads to the synthesis of volatile organic compounds (VOCs), which might be considered as the indicators of spoilage and causing off-odors in highly perishable foods, like raw fish. 

Purpose: The objectives of this study were to select specific spoilage organism (SSO) and to identify VOCs as possible indicators of freshness of raw salmon fillets stored aerobically at different temperatures. 

Methods: The growth of total viable count (TVC), psychrotrophs, Pseudomonas spp., coliforms, lactic acid bacteria (LAB), Brochothrix thermosphacta, H₂S producing bacteria, yeasts and molds were investigated. The VOCs profiles were determined using HS-SPME-GC-MS. Weighted samples of salmon fillets were stored at 4 and 10°C for 14 days and 21°C for 3 days, respectively. SSO and volatile indicators were identified with use of modeling, statistical and multivariate analysis.

Results: Shewanella putrefaciens-like bacteria (H₂S producing bacteria) can be considered as SSO for aerobically stored salmon fillets, as it was characterized by the highest maximum growth rate at 4°C. However, spoiled salmon samples were dominated by: psychrotrophs, probably with Pseudomonas spp., as major representative, followed by B. thermospacta and H₂S producing bacteria. The predicted shelf lives of salmon fillets, at TVC = 7.0 CFU/g, were 3.02, 1.82 and 0.60 days for storage at 4, 10 and 21°C, respectively. While, the sensory rejection point was observed at TVC = 7.5 CFU/g (on 4^thday at 4°C). Regardless of storage temperature, significant (P < 0.05) and high correlations between microbial counts and selected VOCs were observed for trimethylamine, ethanol, 3-methyl-1-butanol, acetoin, acetic acid and 2,3-butanediol. 

Significance: This study showed that the identified VOCs might be suitable as indicators of rapid spoilage detection for aerobically stored fresh salmon.