Effect of Buffered Vinegar on Growth of Staphylococcus aureus and Enterotoxin Production

Introduction: Staphylococcus aureus commonly associated with humans and handling has potential to be a pathogen of safety concern in canned tuna products; produced from eviscerated tuna which is pre-cooked to facilitate separation of meat from skin and bones. S. aureus cells can be thermally inactivated but enterotoxins produced cannot be eliminated during canning process.

Purpose: This study evaluated the effect of buffered vinegar (V) on growth and enterotoxin production by S. aureus in broth and simple food model.

Methods: Buffered vinegar (0.15%, 0.3%, 0.5%) was evaluated using Bioscreen to determine efficacy against four strains and cocktail of S. aureus (6 log CFU/ml). Testing was done to study growth (Baird Parker) and enterotoxin formation (3M SETVIA Staph Enterotoxin Kit) of S. aureus (4 log CFU/ml, n = 2) in 5% and 7.5% V solution in TSB and 0.15% and 3% (attached concentration on food sample upon spraying solution with 3% pick-up) tuna slurry (50 g pre-cooked tuna in 150 ml DI water) at 37°C (0 h, 4 h, 6 h, 8 h, 12 h) and 21°C (0 h, 12 h, 24 h, 32 h, 48 h).

Results: Bioscreen results indicated growth reduction (turbidity) in S. aureus with V; 7.35%, 14.87% and 36.34% with 0.15%, 0.3% and 0.5% V, respectively. V showed an inhibitory effect, S. aureus were 1.1 - 2.6 and 1.2 - 2.8 log CFU/ml lower than controls in treated tuna slurry and broth at 37°C and 21°C, respectively. Bacterial counts in control increased to over 6 log CFU/ml within 8 h at 37°C and in 32 h at 21°C and toxin formation was observed; while all treated samples showed negative results in the toxin test. Testing is in progress to determine spray application of V on pre-cooked tuna meat to control S. aureus.

Significance: V can be used as a potential intervention method to control growth of S. aureus and prevent enterotoxin formation during canned tuna processing.