The spoilage microbiota of ray (Raja sp.) during ice storage under different conditions: Molecular identification and characterisation of the spoilage potential
Broekaert, K.; Noseda, B.; Heyndrickx, M.; Vlaemynck, G.; Devlieghere, F. (2012). The spoilage microbiota of ray (Raja sp.) during ice storage under different conditions: Molecular identification and characterisation of the spoilage potential, in: Broekaert, K. Molecular identification of the dominant microbiota and their spoilage potential of Crangon crangon and Raja sp. pp. 93-118 In: Broekaert, K. (2012). Molecular identification of the dominant microbiota and their spoilage potential of Crangon crangon and Raja sp. PhD Thesis. Ghent University; Faculty of Bioscience Engineering: Gent. ISBN 978-90-5989-499-0. 157 pp., more |
| Abstract | The dominant microbiota of ray stored on ice was systematically identified. Isolates grown on various media were identified by partial 16S rRNA, gyrB and rpoB gene sequencing. Microbiological shifts were observed during storage, ending in a dominance of especially members of the genera Pseudomonas and Psychrobacter. Most isolates could be identified by rpoB (Pseudomonas spp.) or gyrB gene sequencing as Pseudomonas fluorescens, Pseudomonas fragi, Pseudomonas psychrophila, Psychrobacter cibarius, Psychrobacter cryohalolentis, Psychrobacter glacincola and Psychrobacter immobilis. Also species from the genera Arthrobacter, Flavobacterium, Pseudoalteromonas, Shewanella and Staphylococcus were detected during storage of ray. Subsequently, the spoilage potential of six selected isolates (Flavobacterium tegetincola, Pseudomonas fluorescens, Pseudomonas psychrophila, Psychrobacter cibarius, Psychrobacter cryohalolentis and Shewanella frigidimarina) was determined and quantified based on the presence of VOCs. Additionally, API ZYM and urease analyses determined the species’ enzymatic capacity to contribute to spoilage by degrading lipids, amino acids and proteins and breaking down urea to ammonia. The six isolates were inoculated separately as pure cultures on gamma-sterilised ray. The inoculated samples were stored at 4°C and the production of VOCs by the pure strains on the ray matrix was identified via gas chromatography coupled to mass spectrometry (GC-MS). VOC production was quantified by selected ion flow tube mass spectrometry (SIFT-MS). The sensory profile of the selected species revealed that especially Psychrobacter cibarius and Pseudomonas psychrophila were able to produce higher concentrations of VOCs and might be responsible for the off-odours produced during spoilage of ray. |
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