Growth of Staphylococcus aureus and enterotoxin production in pre-cooked tuna meat

This study investigated growth of enterotoxin-producing Staphylococcus aureus and time–temperature combinations needed for enterotoxin production in pre-cooked tuna meat. Frozen samples (50 ± 5 g) of pre-cooked albacore tuna (loin, chunk and flake) and skipjack tuna (chunk and flake) were thawed overnight at 5–7 °C, inoculated with five strains of S. aureus (2–4 log CFU/g), and incubated at 37 and 27 °C for up to 36 h. Changes of S. aureus populations in samples during incubation were determined by plating on Baird–Parker media. Results indicate that increases in S. aureus populations varied among the 5 types of tuna samples. Incubation at 37 °C for at least 6 or 8 h was required to allow an increase in S. aureus populations by >3 log CFU/g in inoculated albacore or skipjack tuna meat. A similar increase of S. aureus counts (>3 log CFU/g) in albacore and skipjack samples required more than 8 and 10 h, respectively, when samples were incubated at 27 °C. No enterotoxin was produced in albacore or skipjack tuna meat inoculated with five strains of enterotoxin-producing S. aureus and exposed to 37 °C for 12 h or 27 °C for 16 h. All the samples showed clear sign of spoilage before enterotoxin was detected.