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.