Biological ensilage of fish - optimization of stability, safety and functionality

This thesis deals with stability, safety, and functionality aspects of biological fish silage (BFS) obtained by lactic acid fermentation. BFS may provide an economically viable, environment friendly way of upgrading fish waste.BFS has been found advantageous when compared to the so-called acid process, since it yielded lower levels of peroxides in the silage oil and led to lower non-protein nitrogen values. Fermentation by lactic acid bacteria (LAB) was shown to efficiently inhibit pathogens such as L. monocytogenes and E. coli O157:H7 as well as some spoilage microorganisms. Histamine degradation by some of the most promising available LAB strains was also tested, as an innovative means of ensuring low levels of this amine in the fermented product. Several potential starter strains were found to degrade histamine as single strain cultures and could find application in fish silage and other fish products in which histamine accumulation might pose a certain risk.Temperatures of 35 - 37°C were regarded as most suitable from the point of view of starter growth and acidification. Strains with a short acidification lag time, such as Lb. plantarum 009, or with very fast growth and good antibacterial properties, such as Lb. curvatus 15.35, are most suitable.Sodium chloride inhibited growth of biogenic amine producing bacteria and additionally decreased non-protein nitrogen and total volatile basic nitrogen values in BFS. Potassium sorbate was shown to inhibit growth and/or acidification by potential starter lactic acid bacteria