EFFECTS OF NISIN,CHITOSAN AND MODIFIED ATMOSPHERE PACKAGING (MAP) IN HURDLE TECHNOLOGY FOR PRESERVATION OF COLD-SMOKED SALMON

• Main Author: Arif, Aimen
• Format: Dissertation
• Language: English

Cold-smoked salmon(CSS) is a popular delicacy worldwide due to its unique taste and texture. However, the presence of pathogenic bacteria such as Listeria monocytogenes creates a substantial health and food safety risk in CSS. The safety measures applied during CSS production are insufficient to inhibit this bacteria's growth. Additionally, CSS often gets contaminated with L. monocytogenes at the production facilities. These issues highlight the need for preservation methods that effectively inhibit bacterial growth in CSS and enhance the product's safety and shelf life. In recent years, hurdle technologies, including bacteriocins (i.e., nisin), antimicrobials (chitosan), and modified atmosphere packaging (MAP), have shown impressive results in preserving and inhibiting microbial growth in ready-to-eat products. The study aims to assess the effectiveness of nisin, chitosan, and MAP in hurdle technology to inhibit the growth of L. monocytogenes in CSS. The efficacy of these antimicrobials was evaluated, both individually and combined, on some Gram-negative bacterial species such as Photobacterium phosphoreum, Escherichia coli, and non-pathogenic Vibrio cholera. The experiments involved in vitro and in vivo methods. In in vitro assays, effectiveness of nisin and chitosan (individual and combined) was evaluated against both Gram-negative and Gram-positive species. However, in vitro method in combination with different MAP atmospheres was applied only against a single strain of L. monocytogenes Scott A. Moreover, challenge studies were performed on CSS real produce inoculated with three strains of L. monocytogenes to determine the individual and combined efficacy of nisin and chitosan with MAP and vacuum packaging. The findings showed that nisin at a low concentration effectively inhibited the growth of Gram-positive strains. Gram-negative E. coli and V. cholera were resistant to nisin; however, P. phosphoreum was highly sensitive to nisin. All species tested were sensitive to chitosan. Combined application of nisin and chitosan effectively reduced the growth of Scott A in CSS fillets kept at 4 °C under vacuum packaging for six weeks. The inhibiting effect was significantly more pronounced when packed under MAP. However, it is not yet clear whether there is a synergistic effect between MAP and the antimicrobials applied. These results show that a combination of nisin, chitosan, and CO2 can inhibit the growth of L. monocytogenes in CSS, contributing to less foo