Biopreservation of Ready-to-Eat Seafood Using Lactic Acid Bacteria Against Listeria monocytogenes
Master thesis
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https://hdl.handle.net/11250/3145659Utgivelsesdato
2024Metadata
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Sammendrag
Seafood is a healthy, nutritious diet that can promote the growth of various pathogens. Pathogenic bacteria that can be commonly present in seafood are Listeria monocytogenes, Escherichia coli, Salmonella species, and Staphylococcus aureus. Among them, L. monocytogenes is the major pathogen in the fish-related products. Therefore, to combat such food pathogens, the need to develop mild preservation methods prevails. Biopreservation is one option that utilizes microbes or their metabolites to prevent pathogens in food while preserving its nutritional and sensory characteristics. Lactic acid bacteria (LAB) are potential candidates for this purpose as they produce various antimicrobial metabolites i.e.; bacteriocins or bacteriocin-like substances. Furthermore, their genera Leuconostoc and Carnobacterium are inherently present in fish microbiota. They can survive various processing conditions thus making them ideal for biopreservation.
The present study aimed to investigate the intraspecies variation of L.monocytogenes tolerance towards biopreservative LAB strains. Four strains of LAB, Carnobacterium divergens 468, C. maltaromaticum 55, C.maltaromaticum 35, and Leuconostoc geldium 406 were evaluated in BHI model system at 15°C for this purpose. The findings suggested that there is a significant difference in the effectiveness of these LAB strains (P<0.001). C. divergens 468 exhibited the highest inhibition, C.maltaromaticum 55 demonstrated medium inhibition, while C.maltaromaticum 35 and L. geldium 406 demonstrated minimal inhibition. Regarding the intraspecies variation of L. monocytogenes strains towards LAB strains, the variations observed between groups was greater than that of within groups. Subsequently, another experiment examined the inhibitory effect of C. divergens 468 on the growth of Listeria strain in fresh vacuum-packed salmon at two different temperatures i.e.; 4°C and 8°C, over a storage period of 16 days, aiming to elucidate the effect of different temperature conditions on the growth of LAB and target strains. LAB strain C. divergens 468 effectively prevented the growth of Listeria in the actual product at both temperatures, indicating its potential as a biocontrol agent.
The complex interaction between varying initial concentrations (log 3, log 5, and log 7 CFU/g) of LAB i.e.; C. divergens 468 and L. innocua in fresh vacuum-packed salmon stored at 4°C for 16 days, was also examined further in the study. Despite having difficulties in achieving initial concentrations of the strains and observing fluctuations in growth rates, this experiment revealed valuable insights into concentration-dependent interactions governing LAB-L.innocua dynamics in salmon preservation and revealed that Listeria faces a reduction in growth depending upon LAB initial concentrations. These findings underscore the importance of further analyzing microbial behaviors within food matrices to devise effective strategies for enhancing food safety and shelf life.
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Full text available on 2026-05-16