Addition of bacteriocins to inhibitListeria monocytogenes in Toroi: a traditional food of New Zealand Mãori

The effectiveness of nisin and sakacin A-producingLactobacillus sakei Lb706 to inhibitListeria monocytogenes was determined in Toroi, a traditional Mãori food. Toroi is a mixture of boiled green vegetable and uncooked mussels that it typically stored in a refrigerator for 2 weeks to 2 months before being eaten. Three batches of Toroi were contaminated with 2.4×103 CFU g−1L. monocytogenes L70; a strain derived from NZ mussels, and stored at 4–6 °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 ofL. sakei Lb706 (4.6×107 CFU g−1 Toroi) resulted in a rapid decline inL. 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 2×105 CFU g−1L. monocytogenes. As Toroi prepared from satisfactory ingredients would be unlikely to contain more than 103 CFU g−1L. monocytogenes, addition ofL. sakei Lb706 could be a useful and practical strategy to reduce a risk of listeriosis.