Exploring the Brine Microbiota of a Traditional Norwegian Fermented Fish Product (Rakfisk) from Six Different Producers during Two Consecutive Seasonal Productions

Abstract

<jats:p>The purpose of this study was to explore the microbiota of Norwegian fermented fish (rakfisk), a traditional product popular in the Norwegian market. Brine samples, collected from six producers during two subsequent years, were used. The producers applied different salt concentrations (between 3.8% and 7.2% NaCl), ripening temperatures (between 3.5 and 7.5 °C), fish species (trout or char), and fish upbringing (wild trout, on-shore farmed trout or char, and off-shore farmed char). The microbiota in the brine during the ripening process was mainly characterized by DNA-based, culture-independent methods. In total, 1710 samples were processed and of these 1342 were used for the final analysis. The microbiota was dominated by Gammaproteobacteria and Bacilli with the largest variance between samples associated with the genera Psychrobacter and Lactobacillus. The variance in the material was mainly determined by the origin of the samples, i.e., the different producers. The microbiota from the individual producers was to a large extent reproducible from one year to the next and appeared to be determined by the relatively small differences in the salinity and the ripening temperature. This is the first study exploring the microbiota in rakfisk brine and it provides insights into environmental factors affecting the rakfisk ecosystems.</jats:p>

Growth Behavior of Listeria monocytogenes in a Traditional Norwegian Fermented Fish Product (Rakfisk), and Its Inhibition through Bacteriophage Addition

“…For logistic reasons explained previously and not to disturb the fermentation [13], brine samples were used for microbiological analysis. Brine samples were collected from the containers on days zero, three, seven, 14, 28, 42, 63, and 91.…”

“…Brine samples were collected from the containers on days zero, three, seven, 14, 28, 42, 63, and 91. In order to minimize moving the fish during sampling and to avoid opening the container lids which would create a disturbance, we employed a previously described sampling system [13]. Tubes with a diameter of approximately 5 cm perforated with 1-cm 2 holes were placed along the container side.…”

“…The safety and efficacy of the P100 phage for reduction of pathogens on different RTE foods were evaluated by the European Food Safety Authority (EFSA) panel on biological hazards [28], and the phage was granted GRAS (generally recognized as safe) status by the FDA in USA for use up to 10 9 plaque-forming units/g food [29]. We recently characterized the microbiota in rakfisk brine of six producers during the course of normal production [13]. However, to our knowledge, there are currently no publications where the actual behavior of L. monocytogenes in the production of rakfisk is described.…”

“…The purpose of the present work was to determine the effect of different ripening temperatures and salt concentrations on the growth and viability of a mix of L. monocytogenes strains during rakfisk production. The chosen salt concentrations and temperatures reflect the prevailing types of commercial rakfisk production [13]. We also examined the effects of the bacteriophage Listex P100 on L. monocytogenes in brine during the rakfisk ripening process and on vacuum-packed rakfisk fillets.…”

Performance of Fluorescence and Diffuse Reflectance Hyperspectral Imaging for Characterization of Lutefisk: A Traditional Norwegian Fish Dish

“…Nordic cuisines are surprisingly diverse, with a variety of fish dishes prepared in such a way that complex processes of biochemical transformations and microbial changes take place [1][2][3]. Lutefisk is one of these dishes whose preparation method is particularly special and uncommon.…”