Abstract
The behavior of Listeria monocytogenes in various seasoning liquids, salted cod roe samples and the manufacturing process of Karashi-Mentaiko (red-pepper seasoned cod roe) was examined. A proliferative test on L. monocytogenes FCI-Lis 10 strain (serovar 1/2a) in three home-made seasoning liquids (pH 5.9, 6.5 and 7.0; Aw 0.95) and four commercial seasoning liquids (pH 5.7-6.1;Aw 0.89-0.93) was performed at 6 and 15°C. The number of FCI-Lis 10strains decreased as the preservation period increased, except of 15°C preservation using home-made seasoning liquid (pH 7.0). A proliferative test on the FCI-Lis10 strain in salted cod roe samples (pH 6.0, 6.5 and 7.0; Aw 0.97) was also performed. The number of FCI-Lis 10 strains increased at 6 and 15°C in the order of pH 7.0>6.5>6.0;however, in the test of 6°C preservation at pH 6.0, the number on the 14th day was almost the same as the inoculated bacterial count. The behavior of the FCI-Lis10 strain was examined in the manufacturing process of Karashi-Mentaiko using the above home-made seasoning liquids and two commercial seasoning liquids (pH 5.7 and 6.0; Aw 0.93). The number of FCI-Lis 10 strains decreased in the manufacturing process regardless of the kind of seasoning liquid . The behavior of the FCI-Lis 12 strain (serovar 1/2b), FCI-Lis29 strain (serovar 3 a) and LM 17 strain (serovar 4b) was examined in the manufacturing process of a home-made seasoning liquid (pH 5.9; Aw 0.95) and two commercial seasoning liquids (pH 5.7 and 6.0; Aw 0.93). The number of all three strains also decreased in the manufacturing process. These results suggest that the growth of L. monocytogenes at 6°C in seasoning liquid, salted cod roe sample and during the manufacturing process is controlled by pH, Aw and temperature, and the control point of L. monocytogenes in the manufacturing process is to use a seasoning liquid with low pH and low Aw, and manufacture under low temperature refrigeration.
