Examination of the experimental conditions in using the LAL/GNB method for judging food irradiation
2008
Koshikawa, T.(Japan Radioisotope Association, Koka, Shiga (Japan). Koka Lab.) | Matsushima, M. | Hironiwa, T. | Miyahara, M.
We examined the use of the Limulus amoebocyte lysate (LAL) test in conjuction with a Gram negative bacteria (GNB) plate count to judge whether food had been irradiated or not, and compared the experimental conditions with those for the European Standard EN 14569:2004. The cultivation temperature at 30 deg C (EN:21 deg C) and period for 72 hours (EN:24+- 1 hours) was suitable for total bacteria (TB) and GNB counts. The calculation of number of TB and GNB on the basis of the colonies in each dish containing 30 to 300 colonies was necessary to perform accurate evaluations. In the endotoxin determination, because of the difficulty of determining whether the gel formed or not by using the European Standard method, the initial cell suspension was diluted with endotoxin-free water by using microtiter plate. The LAL test was applied to each diluted solution in the test tube. Gel formation was confirmed easily. Confirmation of irradiation was possible by using the 'A-value' expressed by [logsub(10)(Endotoxine/g) - logsub(10)(GNB/g)]. Positive A-values were judged to indicate the sample was properly 'irradiated', and negative A-values, when the total (or GN) bactera count was over 10E3 CFU/g, to indicate the sample was 'unirradiated'. When negative A-values were obtained with a bacterial count less than 10E3 CFU/g, a strong possiblity of irradiation was suggested.
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