The bacterial flora of vacuum-packed cold-smoked salmon stored at 7°C, identified by direct 16S rRNA gene analysis and pure culture technique

Abstract

Aims: The indigenous flora of freshly chilled cold‐smoked salmon just after the vacuum packaging, and the spoilage flora after storage, in vacuum package at 7°C for 19 days, were to be investigated with two different sampling strategies. Methods and Results: Identification was performed using 16S rRNA sequencing of both isolated bacteria and bacterial DNA from tissue extract. The indigenous flora of fresh cold‐smoked vacuum‐packed salmon was dominated by, in order, Brochothrix thermosphacta, Yersinia ruckeri, Photobacterium and Carnobacterium, whereas the spoilage flora of the same product stored at 7°C for 19 days was dominated by Lactobacillus and Photobacterium. The two sampling strategies showed similar results on the fish flora. Several new types of Photobacterium sequences, closely related to Photobacterium iliopiscarium and Photobacterium phosphoreum, were found from both the freshly processed and the stored salmon, indicating that smoked salmon harbours at least three different, as yet unknown, Photobacterium species. Conclusions: Ten per cent of the bacterial flora multiplying on chilled, vacuum‐packed, cold‐smoked salmon comprised unknown species. The two sampling strategies complement each other. Significance and Impact of the Study: As cold‐smoked salmon is consumed without heat‐treatment, the presence of undefined bacteria in high numbers should be considered in public health assessments.

Quality assessment of ice-stored tropical yellowfin tuna (Thunnus albacares) and influence of vacuum and modified atmosphere packaging

“…After 13 days, total microbial counts reached 6-7 Log CFU g -1 , which is considered the limit of acceptability for freshwater and marine fish (ICMSF, 1986). Initially, a majority (93%) of gram-negative bacteria was (Hovda et al, 2007b;Jaffrès et al, 2009;Kakouri and Nychas, 1994;Koutsoumanis and Nychas, 1999;Mamlouk et al, 2012;Mejlholm et al, 2005;Nychas et al, 2008) or in lightly preserved VP products (Olofsson et al, 2007), but more rarely from fish stored under air (Noseda et al, 2012). On the contrary, Pseudomonas spp., particularly P. fragi, is often reported to be responsible for sweet and fruity off-odors in fish flesh stored under air (Gennari et al, 1999;Gram and Huss, 1996;Hovda et al, 2007a;Hozbor et al, 2006;Koutsoumanis and Nychas, 1999;Miller et al, 1973;Ola and Oladipo, 2004;Parlapani et al, 2015a;Parlapani et al, 2015b;Parlapani and Boziaris, 2016;Ravi Sankar et al, 2008).…”

Microbiological changes, shelf life and identification of initial and spoilage microbiota of sea bream fillets stored under various conditions using 16S rRNA gene analysis

“…The application of molecular techniques in foods has changed how microbial communities are explored . 16S rRNA gene sequence analysis is currently the most common approach for studying seafood microbiota grown on plates . Microorganisms grown on laboratory media are easily isolated and identified using only a small amount of DNA.…”

Origin and ecological selection of core and food-specific bacterial communities associated with meat and seafood spoilage

“…Furthermore, smoked salmon contained 14 unique OTUs not found in salmon fillet samples, indicating likely a post contamination during the washing/smoking. These OTUs mostly belong to Photobacterium, a water-borne genus commonly associated with seafood spoilage (Dalgaard, 1995;Gram and Huss, 1996;Leroi et al, 1998;Joffraud et al, 2006;Hovda et al, 2007;Olofsson et al, 2007;Reynisson et al, 2009;Macé et al, 2013). The cooked shrimp cluster (59 OTUs) also contained two distinct groups: (1) OTUs affiliated to well-known thermal resistant bacteria (Exiguobacterium, Rhodobacteriaceae and Chromatiaceae) from geothermal deep sea sediments (Rodrigues et al, 2008;Broekaert et al, 2013) that may have been selected for by the precooking process; (2) OTUs linked with putative uncultured endosymbionts in the phyla Tenericutes and Proteobacteria (Kostanjsek et al, 2007;Robidart et al, 2008;Nechitaylo et al, 2009).…”

“…g À 1 ). (see Ercolini et al, 2006;Joffraud et al, 2006;Jaffrès et al, 2011;Jiang et al, 2011;De Filippis et al, 2013;Macé et al, 2013;Olsson et al, 2003;Olofsson et al, 2007;Reynisson et al, 2009;Nieminen et al, 2012;Sade et al, 2013 for recent research). Yeasts and molds are also present but these micro-organisms are rarely monitored as spoilers because they usually form a subdominant microbiota (ca.…”