Radiation treatment is getting important position for sterilizing medical devices and for packaging films of foods. Recently, survey of bioburden is an important technique for evaluation of sterility doses for medical devices. However, many studies have been done mainly on the irradiation effects of spore-forming bacteria in medical devices. In this study, radiation sensitivity of spore-forming bacteria and fungi were examined after the survey on distribution of microorganisms in several kinds ofmedical devices.
The main contaminant in disposable syringes, needles and conical flasks were consisted of Bacillus, with lesser amount of Micrococcus, Pseudomonas, Peptococcaceae and fungi as positive of 5-60% in the medical devices which cultivated in thioglycolate broth. Bacillus group were identified as B. pumilus, B. sphaericus, B. coagulans, B. megaterium and etc. Fungi were isolated a lesser amounts compared with spore-forming bacteria and identified as Blastomyces, Penicillium, Haplosporangium, Euricoa and Audeobasidium (Table 1, 2). Peptococaceae were not isolated after irradiation with a dose of 0.1 Mrad even the samples were contaminated with high percentage (Table 3).
The D₁₀ values of dryed endospores of Bacillus-isolates which attached to the filter paper with pepton-glycerin were obtained tobe 0.11-0.19 Mrad (Table 4). The D₁₀ values of many isolates of fungi in dry condition were obtained below 0.08 Mrad (Fig.1). However, the isolate of Aureobasidium is radiation-resistant, and it's D₁₀ values was obtained as 0.28 Mrad under aerobic and anaerobic dry condition (Figs.2, 3).
From these results, it is possible to sterilize safely all of disposable medical devices by a dose of 2.0-2.5 Mrad, with a sterility assurance level being below 10^-6(Table 5).

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Buckwheat flour is a major compositional material of ‘soba’ noodle which is a very favorable traditional dish among the Japanese. Against the characteristic properties in flavor and texture as well as the nutritious values, one decisive defect for Buckwheat Flour and processed buckwheat foods is the microbial contamination. The count in microorganisms on these materials is generally much larger than the count on wheat flour by several logarithmic figures per gram. Because of its heat sensitive flavor and tastareany thermal sterilizing procedures can not be applicable to buckwheat flour.
The purpose of this series of studies is to develope a practical shelf-life extension method for fresh style ‘soba’ noodle by use of non-thermal treatment, or ionizing irradiation, to inactivate microorganisms. The latent unsanitary practices in trades and industrial processes are also required for reformations. This paper describes the basic experimental results as follows:
1. The standard plate count in microorganisms on most of the irradiated materials such as buckwheat grains with hulls, industrially processed buckwheat flours, and uncooked ‘soba’ noodles packed in plastic film bags, decreased to the level smaller than 1×10² per gram, at the dose level of 0.5 Mrad or lower dose (as shown in Fig. 2 thru Fig. 4) . The effective dose to decrease 90% of count in microorganisms was around 0.1 Mrad for the buckwheat flours, at the dose level between 0.05 and 0.5 Mrad.
The heat resistant microorganisms in these buckwheat flours decreased to counts smaller than 10 microorganisms per gram by 0.2 to 0.5 Mrad dose (as shown in Table 3) .
2. The direct irradiation to buckwheat grains with hulls rather enhanced the desirable ‘soba’-like flavor of the experimentally milled buckwheat flour and the trial ‘soba’ noodles processed succeedingly. The unexpected good result was obtained only in one performance, though.
So-called ‘off flavor by irradiation’ was not significantly detected for the irradiated fresh-style ‘soba’ noodles which were processed at a ‘soba’ factory.
3. Decrease of viscosity for 9% aqueous suspension of the irradiated buckwheat flour was observed in a Brabender's Viscographic analysis. But, the ‘soba’ noodle processing property of buckwheat flour was little affected by irradiation treatment.
The textural property of the conventional fresh-style ‘soba’ noodle became poorer by irradiation, which might be caused partly by the degraded wheat flour, one compositional part of that ‘soba’ noodle.
4. In conclusion, the use of gamma irradiation for inactivation of microorganisms in buckwheat flour was considered to be practical. Irradiation to raw material grains with hulls as well as to processed ‘soba’ noodles was also considered to be useful.
The related problems for the possible commercial application of gamma irradiation to buckwheat grains and others was briefly discussed. A suggestion was added from the view point of world trades. (See Fig. 6.)
The irradiation experiments were supported by courtesy of The Takasaki Research Institute, Japan Atomic Energy Research Organization.

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A few selected varieties of buckwheat flours of the food use grade were irradiated at the dose level between 0.05 Mrad and 1 M rad. Some fundamental properties of the buckwheat flours in ‘soba’-noodle processing were evaluated to get the results as follows:
1) The viscosity of Brabender's viscograph of the buckwheat flour (aq. suspension at 9% concn. level) decreased with the increased dose of gamma irradiation (Fig. 2 and Fig. 3) . It was also considered, however, that the reduced Viscograph-viscosity did not necessarily mean the poor taste score of the processed ‘soba’-noodles.
2) The water soluble proteins (WSP) contents of buckwheat flour were little affected by irradiation. On the contrary, the contents of water soluble sugars (WSS) increased with the increased dose (Fig. 4) . This analytical finding suggested the negligible disadverage by gamma irradiation in the practical ‘soba’-noodle processing.
3) A kind of so-called irradiated-food-flavor, though not so much rejecting one, was organoleptically detected with the increased intense for the irradiated buckwheat flour of higher dosage. The phenomena coincided with the gas chromatograms (Fig. 5-1 to Fig. 5-3), analized ‘headspace volatiles’ collected from the respective buckwheat flours (Fig. 1).
4) The other kind of buckwheat flour, the original Canadian grains (with hull) of which were irradiated at 0.5 Mrad dose level, and then milled with roller-mill, was not organoleptically detected irradiated-food-flavor. Figure 6 showed the gas chromatogram for that sample, for comparision
These basic experimental knowledges presented the possible practical use of gamma-irradiation in food industries related with ‘soba’-noodle processing, the further investigations would be required, though.
The irradiation experiments were supported by courtesy of The Takasaki Radiation Chemistry Research Establishment, JAPAN ATOMIC ENERGY RESEARCH INSTITUTE.

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The characteristic properties of agar and carrageenan were expected to be useful model substances for development of irradiation technology on foods. A few kinds of agars and carrageenans of known origins (listed on Table 1) were used for the irradiation tests to investigate any possible changes in the basic properties of these dry substances and hydro-gels, with respect to ‘melting point of ge’.
1. ‘Melting point of decreased by gamma irradiation.In one example, thegel’ change of ‘melting point of gel’, for agar-A, was reversely proportional to dosage of gamma ray, which was -3.3°C/Mrad at the dose level between 0.1 and 1 Mrad.
2. The extent of decrease in melting point was dependent to individual agar and carrageenan of different origin.
3. The materials irradiated in the state of hydro-gel showed greater decreases in ‘melting point of gel’ than the ones irradiated ih, the state of air-dried matter, in general.
4. ‘Melting point of gel’ was discussed to be a significant indicator which could evaluate gelling property of these colloidal substances. Consequently, a possible use of agar in an indirect examination of irradiation dose level was suggested.
The decrease in ‘melting point of gel’, at least in the case of irradiation to dry substance, was considered to be an irreversible change.

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The effects of gamma-irradiation (0.5-5.0 kGy) on micro-components, odor and taste of boiled water extractives of sardineand its two times diluted extractives were examined.
The irradiation of both extractives with 2.0 kGy was slightly weaker in fishy odor than that of unirradiated controls by Scheffe's period method (Fig.1).
No increase and decrease of odor (ether like and sulfury), amino acid content (Table1), carbonyl compounds (acetaldehyde, propylaldehyde, n-butylaldehyde and iso-valeraldehyde), crudeprotein, and pH of both extractives by irradiation were almost recognized.
Hydrogen sulfide and dimethyl disulfide in volatile sulfur compounds in the extractives slightly increased with an increase of irradiation dose, and methyl mercaptan decreased with 1.5 and 2.0 kGy (Fig.2). From the results and the results of decrease of methionine in the extractives by irradiation, radiolytic pathway: methionine → methyl mercaptan → dimethyl disulfide was estimated.

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