Addition of bacteriocins to inhibit Listeria monocytogenes in Toroi:: a traditional food of New Zealand Maori

The effectiveness of nisin and sakacin A-producing Lactobacillus sakei Lb706 to inhibit Listeria monocytogenes was determined in Toroi, a traditional Maori food. Toroi is a mixture of boiled green vegetable and uncooked mussels that is typically stored in a refrigerator for 2 weeks to 2 months before being eaten. Three batches of Toroi were contaminated with 2.4 x 10(3) CFU g(-1) L. monocytogenes L70; a strain derived from NZ mussels, and stored at 4-6 degrees C. When nisin was added to Toroi at 1000 IU g(-1) (final concentration) L. monocytogenes numbers declined (c. 0.5 log) but had returned to the initial level by 14 days. In contrast, addition of L. sakei Lb706 (4.6 x 10(7) CFU g(-1) Toroi) resulted in a rapid decline in L. monocytogenes to a very low level (< 10 CFU g(-1)) with no increase over 2 months. However, L. sakei Lb706 was not effective for Toroi that contained 2 x 10(5) CFU g(-1) L. monocytogenes. As Toroi prepared from satisfactory ingredients would be unlikely to contain more than 10(3) CFU g(-1) L. monocytogenes, addition of L. sakei Lb706 could be a useful and practical strategy to reduce a risk of listeriosis.