Volatile organic compounds of microbial and non-microbial origin produced on model fish substrate un-inoculated and inoculated with gilt-head sea bream spoilage bacteria

Abstract

Volatile organic compounds (VOCs) origination during fish spoilage is attributed to either decomposition of fish constituents or metabolic activity of spoilage bacteria. To identify microbiological spoilage markers it is essential to know which VOCs are microbial metabolites. VOCs produced in sterile fish juice agar (FJA) model substrate made from gilt-head sea bream (Sparus aurata) flesh juice, inoculated or not with spoilage bacteria isolated from sea bream fillets were detected using SPME/GC-MS technique. Three groups of spoilage bacteria (Pseudomonas, Shewanella and Carnobacterium/Lactobacillus strains) were used to inoculate Petridishes with FJA and stored at 0 and 15 °C under air and commercial Modified Atmosphere Package (MAP CO2: 60%, O2: 10%, N2: 30%). Bacterial growth was also monitored. VOCs that were detected in sterile substrate and their amounts were not higher in inoculated FJA were presumably of non-microbial origin. VOCs that were detected only in inoculated FJA were metabolic products of spoilage bacteria. Some of VOCs were associated with metabolic activity of a particular microbial group, e.g. ethyl esters were associated with Pseudomonas, while 2-, 3-methylbutanal and 3-hydroxy-2-butanone with LAB. Few microbial metabolites increased during storage showing their potential as spoilage markers of gilt-head sea bream and the possible use for rapid freshness assessment. © 2016 Elsevier Ltd