Antimicrobial effects of garlic, clove and red hot chilli on Listeria monocytogenes in broth model systems and soft cheese

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Antimicrobial activity of 1% (w/v) fresh garlic, ground clove and red dried chilli on Listeria monocytogenes was tested in broth systems at 37°C and at 4°C for 7 h. The initial cell concentration in the broth systems was between 2×106 and 4×106 CFU/ml. At 37°C, growth to viable numbers of 3×108 CFU/ml in 7 h was measured. Clove had bacteriocidal activity and reduced the count to 1 CFU/ml. Garlic displayed bacteriostatic properties, and a count of 4×106 CFU/ml was maintained. Red chilli displayed an inhibitory effect and resulted in 50% lower counts than the control. L. monocytogenes had a slow growth rate at 4°C and increased from an initial value of 3×106 to 5×106 CFU/ml during 7 h. The addition of garlic resulted in 3×106 CFU/ml, and clove reduced the viable cell concentration to 1×103 CFU/ml after 7 h. Two batches of soft cheese were produced in the laboratory using milk that was supplemented with L. monocytogenes. The final cheese containing L. monocytogenes with about 1×105 CFU/g. Half of each cheese batch was supplemented with either 1% garlic or 1% clove, whereby the other half served as a control. After 7 or 11 days incubation at 4°C, the cheese was incubated at abuse temperature of 25°C for 7 or 3 days, respectively. No antimicrobial effects of 1% (w/w) fresh garlic or clove powder on L. monocytogenes were observed in cheese after 1 or 2 weeks at the lower or higher temperature.

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