No.4（2009）6.Detection of irradiation history of seasoning mixes composed of dried fish and its extract

Masayuki Sekiguchi, Seiko Nakagawa, Syunji Yunoki

  In the present study, the thermoluminescence (TL) method (EN1788) was used to detect the irradiation treatment of Japanese traditional seasoning mixes mainly composed of dried fish (bonito etc.) and its extract. The Glow 1 curves of minerals separated from the seasoning mixes using a heavy liquid showed significant single peaks at temperatures between 146.5°C and 175.4°C. The peaks are typical for irradiated food, despite the samples being not irradidated. The Glow 2 curves showed single peaks at temperatures higher than that of the Glow 1 curves (175.4°C to 217.9°C). The peak temperature of Glow 2 is usually lower than that of Glow 1 because the peaks from irradiated silicate minerals shift to higher temperatures with time. The TL glow ratios (Glow1/Glow2) calculated in the temperature ranges (167-232°C) defined by means of irradiated TLD-100 were above 0.1, suggesting that the mineral samples were contaminated with organic materials such as protein or bio-inorganic materials such as bone. In order to remove the possible contaminants, acid hydrolysis and subsequent heavy liquid separation were employed. The minerals thus obtained showed no Glow 1 peaks. A significant peak was observed at 213°C instead of peaks at lower temperature for the case of irradiated seasoning mixes (2.45 kGy) . These results suggest that the TL method may provide false positives for the Japanese traditional seasoning mixes because of luminescence from some components other than silicate minerals. It appears that EN1788 needs some modification to precisely detect food irradiation for the seasoning mixes.

Keywords

Thermoluminescence analysis, Irradiated food detection, Mineral separation, EN1788, Fish and its extracts

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