The effect of heat resistance of endospores after gamma-irradiation were investigated for application to decontaminate microorganisms in spices or other dried food materials. D₁₀values of endospores dried on glass fiber filter with additives of 2% peptone + 1% glycerin were obtained to be 1.8 kGy forBacilluspumilus, 1.1 kGy forB. cereus, 2.2 kGy forClostridium botulinumType A and 2.4 kGy forCl. botulinumType E, respectively. Non-irradiated endospores ofB.pumilusand B. cereuswere inactivated with 40 min of heat treatment at 100°C in water. When endospores were irradiated with 5 kGy, these bacteria were inactivated below 20 min of heating at 100°C in water. In the case ofCl. botulinumType A and Type E, non-irradiated endospores were inactivated with 30 min of heat treatment at 100°C in water, and irradiated endospores at 5 kGy were inactivated below 15 min of heating. However, all of these bacteria could not inactivate endospores even after heating more than 2 hours at 100°C in dry condition or 80°C in water, and decreased a little of necessary times for inactivation of heat treatmentafter irradiation at 5 kGy.

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The effect of dry condition of food materials such as spices or herbs with grain or powder were investigated for inactivation of microorganisms by gamma-rays or electron-beams. Radiation sensitivities on endospores ofBacillus pumilusandB. cereusat polished rice, whole black pepper and glass fiber filter dried with additives of 2% peptone + 1% glycerin were almost equivalent, and D10 values of gamma-rays were obtained to be 1.8-2.2 kGy forB. pumilusand 1.2-1.3 kGy forB. cereus, respectively. However, D10 value was decreased to 1.6 kGy forB. pumilusand 1.0 kGy forB. cereusin white pepper powder, and increased significantly as 2.6 kGy forB. pumilusand 1.8 kGy forB. cereusin senna herb powder. In the case ofB. megaterium, Enterobacter cloacaeandEscherichia coli, D₁₀values were increased at all of food materials even in white pepper powder compared with glass fiber filter with additives. These results are indicating that glycerin and related radical scavengers in food components protect the bacteria such asB. megaterium, Ent. cloacaeandE. colimore significantly from effects of radiation thanB. pumilusorB. cereus. The increase of radiation resistance of these bacteria should be responsible also to the amount of oxygen penetration in bacterial cells which dried at different conditions. On the irradiation of electron-beams, radiation resistance of all of bacteria increased more significantly than gamma-rays which depending to dose rate effects on bacteria. However, increase of radiation resistance was not observed atAspergillus oryzaein all of food materials at different dry conditions.

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Hydrocarbons produced from two main fatty acids (oleic acid and palmitic acid) are useful marker for detection of irradiation treatment. The main products, 1-C14: 1, 1, 7-C16: 2, C15: 0 and 8-C17: 1 were measured and their ratios were calculated to identify irradiated meat. As the value of 1-C14: 1/1, 7-C16: 2 was nearly equal to ratio of original fatty acids, the sample was easily detected as irradiated meat. The value of C15: 0/8-C17: 1 can be also used for identification, when the background in nonirradiated meats are low and dose is high enough to be detected hydrocarbon.
As range of electron beam is shorter than that of gamma-ray, distribution of hydrocarbons in sample irradiated with electron beam was examined.
Cylindrically trimmed ground beef meat with the sizes of 70 mm in diameter and 30 mm in height was irradiated with 5 MeV electron beam at surface doses of 5 and 10 kGy. After irradiation, the cylinder was sliced, and hydrocarbon contents were measured in each slice. Amount of hydrocarbon was maximum in the slice obtained at 7-10 mm depth from the surface. Hydrocarbon formation was very few in the slice obtained at 25-30 mm depth of the central part. The study shows depth profile of hydrocarbon formation with 5 MeV electron beam agreed to theoretical depth-dose curve. On the other hand, profound effect of irradiation was observed in peripheral part of the slice of 20-30 mm depth.

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The XII th International Meeting on Radiation Processing was held at Avignon March 25 to 30^th, 2001. Many methods for identification of irradiated foods were presented in the meeting. The 5 standard methods issued by the British Standard Institutes (BSI) were effective since 1997. Most papers were related to the 5 standards. The papers reported 8 extended applications to foods that are not validated by BSI manuals. Comet assay is a new candidate for the standard. Six applications of comet assay and related assay for 17 foods are presented. Viscosity method for grains and nuts, impedance method for potato, and infrared method for milk products were also reported in the conference.

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[in Japanese]

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