Microbiota of lutefisk, a Nordic traditional cod dish with a high pH

Abstract

Most foods have either a neutral or a slightly acidic pH, whereas only a limited number of products have a pH above 8. The Nordic traditional fish dish lutefisk is an exception, with a pH around 12 during production and a ready for consumption pH above 10. Lutefisk is prepared from dried Atlantic cod (Gadus morhua), soaked in water and thereafter treated in a lye solution. During this process, the muscle proteins are partially hydrolyzed and a characteristic smell and a gel like appearance are developed. Due to its high pH, lutefisk has previously been considered not to harbour any microbiota. However, in our study of commercially available lutefisk, aerobic and anaerobic plate counts of up to 1.4 × 106 and 5.5× 104 CFU g−1, respectively were found. The pure culture isolates from Plate count agar, Iron agar Lyngby and Alkaline Nutrient agar, were identified by 16S rRNA gene sequencing as Carnobacterium maltaromaticum, Pseudomonas fragi, Staphylococcus warneri, S. hominis, Aeromonas salmonicida, Kurthia zopfii, Microbacterium oxydans, Exiguobacterium oxidotolerans, Alishewanella tabrizica and Bacillus licheniformis. This is the first report on the microbiota of lutefisk based on cultivation and 16S rRNA gene sequencing.