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

Antimicrobial activity of 1% (w/v) fresh garlic, ground clove and red dried chilli on Listeria monocytogenes was tested in broth systems at 37degreesC and at 4degreesC for 7 h. The initial cell concentration in the broth systems was between 2 x 10(6) and 4 x 10(6) CFU/ml. At 37degreesC, growth to viable numbers of 3 x 10(8) CFU/ml in 7 h was measured. Clove had bacteriocidal activity and reduced the count to I CFU/ml. Garlic displayed bacteriostatic properties, and a count of 4 x 10(6) 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 4degreesC and increased from an initial value of 3 x 10(6) to 5 x 10(6) CFU/ml during 7 h. The addition of garlic resulted in 3 x 10(6) CFU/ml, and clove reduced the viable cell concentration to 1 x 10(3) 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 x 10(5) 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 4degreesC, the cheese was incubated at abuse temperature of 25degreesC 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.