Hi jdebeer,
Thks for above update. Here is abstract of 1st reference -
Abstract: The aim of this study was to determine the time for a 3-log CFU/g outgrowth of Staphylococcus aureus and its toxin production in previously frozen precooked tuna meat (albacore [Thunnus alalunga] prepared as loin, chunk, and flake or skipjack [Katsuwonus pelamis] prepared as chunk and flake) held either at 21 or 27°C.
A five-strain cocktail of enterotoxin-producing S. aureus was surface inoculated with ~10³ CFU/g onto tuna samples. The experimental time-temperature conditions were designed to mimic common industry holding conditions. After a 3-h incubation at 37°C, inoculated samples were individually vacuum sealed and stored at 20°C for 4 weeks [?]. Following frozen storage, samples were thawed to the target temperature (21 or 27°C) and then incubated aerobically. Growth of S. aureus in tuna was then monitored using Baird Parker agar; simultaneously, aerobic plate counts, enterotoxin production, and sensory profile (color and odor) were determined.
The results showed that the time for a 3-log CFU/g increase was >20 h at 21°C and 8 to 12 h at 27°C for albacore, with toxin production observed at 14 to 16 h at 21°C and at 8 h at 27°C. A 3-log CFU/g increase for skipjack occurred at 22 to 24 h at 21°C and at 10 to 14 h at 27°C. The toxin production in skipjack started at 20 to 22 h at 21°C and at 8 to 10 h at 27°C. Toxin production was observed before a 3-log increase was achieved in albacore samples at 21°C. Under all conditions, toxins were detected when the cell density of S. aureus was 6 log CFU/g.
Overall, significantly faster S. aureus growth was observed in albacore compared with skipjack (P < 0.05), possibly owing to differences in sample composition (e.g., pH and salt content).
The data developed from this study can be used by the tuna industry to model the growth and enterotoxin production of S. aureus and to design manufacturing controls that ensure food safety.
It is true that post-handling after cooking is a potential source of contamination with S.aureus and other species. Indeed this is a well-known hazard for all RTE-destined products. The risk will also be related to the time involved. Nonetheless appropriate GMP/environmental temperature should enable control of this hazard.
According to the thesis mentioned, in a typical canning process using frozen, pre-cooked product, the thawing apparently takes place at elevated temperatures. This is also a potential hazard IMO if involving extended times. (IMEX of non-precooked raw materials, the thawing is preferably done at low temperatures to prevent microbial growth. But this of course can substantially increase the process time).
I noticed these 2 thesis comments -
While outbreaks of staphylococcal food poisoning have not been associated with commercially canned tuna, they have been linked to canned, smoked and salted products, boiled paste and sausages where the growth of competing organisms are inhibited (Bryan,1980; Nakano et al., 2004; Simon and Sanjeev, 2007).
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When the pre-cooked tuna meat samples were inoculated with S.aureus at levels of 103-4 CFU/g, SEA [S.aureus enterotoxin A), SEB, and SED were detected in all samples after 36 h of incubation at 37°C. However, a thermal process of 121°C for 15 min or 111°C for 40 min destroyed all enterotoxins.
The published report of above thesis contained these summary comments in the abstract which are somewhat at variance with data in uppermost quote -
Total S. aureus counts in albacore and skipjack samples increased by greater than 3 log CFU/g after 6 and 8 h of exposure to 35 to 37 °C, respectively. All samples became spoiled after 10 h of exposure to 35 to 37 °C, while no enterotoxin was detected in any samples. However, enterotoxins were detected in albacore loin and other samples after 12 and 24 h of incubation at 35 to 37 °C, respectively. Frozen precooked tuna meat should be used for producing canned tuna within 6 to 8 h of thawing to avoid product spoilage and potential enterotoxin production by S. aureus in contaminated precooked tuna meat.
I'm unsure what time/temperature is involved in commercial tuna canning but perhaps the third quote may help to explain the absence of any reported safety incidents for tuna if toxin had been produced.
JFI i attach an additional related (2018) paper -
Microbiological Quality- Safety of Skipjack Tuna Loins for Canning.pdf 393.23KB
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Net result IMO is to reinforce previous conclusion - need actual Process Data.
