Micrococcus radibduranswhich was isolated from canned meat by Anderson et al shows extreme resistance to both ultraviolet light and ionizing radiation. Although the mechanisms of such high resistance are not clear, radiation damages in DNA may be repaired during postirradiation incubation. At relatively higher doses other cellular damages would become critical for viability if repair system for DNA came into play and others were not repaired. We had studied the relationship between changes in survivals and biosynthetic activities for macromolecules in cells. After irradiation with 2×10⁴ rads by ⁶⁰Co γ-rays, no differences in numbers ofviable cells, ¹⁴C-amino acids incorporation into protein and ³²Pi dncorporation into RNA and DNA fraction from non-irradiated control during postirradiation incubation were found. Biosynthetic activities of protein, RNA and DNA were inhibited to the same extent at the dose of 3.5×10⁵ rads (Fig.2 (B) -Fig.5 (B)) though the viable counts were not reduced (Fig.1). At the higher dose of 8.0×10⁵rads, which gave about 3% survivals, incorporations of these labelled precursors into each fraction were inhibited intensely. These results on M. ractiodurans. are different from those as reported with E.coli that synthesis of DNA is considerably prevented by the irradiation while protein and RNA are synthesized at normal rate. Further studies on radiation effects on macromolecular synthesis in radioresistant bacteria are now under way in this laboratory in the hope of elucidating their radiation resistance.

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The effect of some factors on the radiation resistance of spores of Clostridium botulinum type E was studied. The following resultswere obtained.
(1) No significant difference was observed in the radiation resistance of the spores irradiated at 0, 10, and 20°C, It was, however, observed that the radiation death rate decreases with the increasing temperatures between 20°C and 50°C. At temperatures below-10°C, the radiation resistance of the spores increased again . The minimum point of the radiation resistance of the spores was found to be at around 0°C.
(2) Organic and inorganic media were found to offer a slight protecting effect against radiation as compared with distilled water.
(3) Spore suspensions irradiated at equivalent dose levels showed much, less viability with post irradiation incubation temperatures of 10 and 20°C as compared with of 30°C.
(4) A total of 14 type E strains isolated in Hokkaido were tested for their .radiation resistance of spores. The average D-value was 0.138 Mrad, ranging from the maximum value of 0.174 Mrad to the minimum of 0.103 Mrad.

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The radioresistances of 16 species and 39 strains of bacilli spores grown on tryptone glucose extract agar, glucose nutrient agar and yeast extract nutrient agar, were illustrated in Fig. 2 by the dose to give the 10^-4 survival which was obtained from the dose-survival curves (Fig. 1). In some cases, varied radioresistance of the spores of same strain grown in different growing media were observed.
Significance of the concentration level of metals in the growing media on the spore production and on the radioresistanceof the spores were investigated using Bacillus megaterium IMF 1166. A little, spore crop was observed on the media without addition of manganese (Table 2). Variationsin radioresistance of the spores were also observed in theconcentration levels of manganese and calcium added to thegrowing media (Fig. 3 and 4).
Effects of combination of .growing media components, beef extract, yeast extract, peptone and glucose on the radioresistance of spores were examined using Bacillus cereus IMF 1029. Variations in radioresistances of the spores harvestedfrom media having different components were observed in thecomparison of D¹⁰ values (Fig. 5). Different radioresistanceof the spores grown on the potato, milk and beef agar were demonstrated (Fig. 6).
From these observations, it is suggested that the sporulating media compositions must be standardized in the determination of radioresistance of the spores. A significance of the results obtained in practical food irradiationwas discussed.

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The following results were obtained when the spores of B.natto isolated from natto (fermented soybean) were ir-radiated with ⁶⁰Co γ-rays:
1. Irradiation of the spores at 1.86, 3.72 and 7.44× 10⁵ rad resulted in decrease in bacterial counts by 97, 99.7, and 99.996%, respectively. These results are in agreement with those previously reported by Teramoto.
2. Irradiation of 3.7× 10⁵ rad gave a large number of isolates that produce more mucilage than the non-irradiated spores.
3. The isolates obtained by irradiation of more than7.44× 10⁵ rad showed decrease in protease activity and mucilage production.
4. The colonies formed on the synthetic medium fromirradiated spores differed in appearance from those of non-irradiated, although the mucilage produced by the former wasfound to be composed of polyglutamate.

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The cell of a strain of Rhodotorula sp. (Rh-110) isolated by the authors, contains 10-45 per cent of crude fat and 45-20 per cent of protein. In general, both fatty acid and ergasterol content of the metabolites of the Rh-110 strain is quite constant, being independent from the culture conditions employed.Therefore, it is expected that particular mutant which is to be obtained in irradiation might give specifically varied contents of fatty acids and ergosterol.
The present paper reports general characteristics of such mutant strains obtained.

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Combined effect of a low level of ionizing radiation (0.1 Mrad) with 3 kinds of food preservatives on the storage life of northern halibut (Hippoglossus stenolepis) and big-eyed tuna (Parathunnus sihi) fillets at 0 °C were studied. The work was conducted concurrently with sensory, chemical and microbiological examinations to evaluate the effectiveness of the combined treatment of the samples with irradiation of Co⁶⁰ γrays and food preservatives for prolonging the storage life at 0 °C.
The test fillets were either dipped in chlortetracycline (CTC, at 10 ppm), furylfuramide (FF, at 5 ppm), or tylosin (T1, at 10 ppm) for 10 minutes, half of the pretreated samples in polyethylene bags were irradiated at 0.1 Mrad of dose at 20 ° ± 1 °C, then subjected to storage under refrigeration at 0 ° ± 0.2 °C for 6 weeks.
As can be seen in Pables 1 and 2, the storage life of fillets was apparently prolonged by receiving such a low dose of radiation as 0.1 Mrad, especially the pretreatment with CTC resulted in elonating the shelf life for two weeks, and with FF for 1 week as compared with simply irradiated control.
On the contrary, almost no marked preservative effect could be seen on the fillets by treating with each of the food preservative solution so far tested.
Similar tendency was observed in the irradiated tuna samples, whereas a marked green discoloration occurred after 3 weeks of storage without giving any sign of putrefaction which made it difficult to evaluate, the combination effect ofirradiation and preservatives.
The mode of decomposition varied according to the kind ofpretreated drug and/or by irradiation. These differences inthe pattern of decomposition are believed to be attributableto the biochemical natures of the tissues of test fish involved, and the microflora associated with the decomposition of fish fillets.

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The microfloral changes in irradiated (0.1 Mrad) and foodpreservative-treated northern halibut and big-eyed tunafillets during aerobic (packaged with thin polyethylene film), refrigerated storage at 0° were determined by the identificationof bacterial and yeast isolates to the generic level.As reported in the previous paper, two species of fish fillets were treated with either chlortetracycline (CTC, at 10 ppm), furylfuramide (FF, at 5 ppm), or tylosin (TL, 10 ppm). Half of which were subjected to irradiation at 0.1 Mrad of Co⁶⁰γ Arays. All the samples being stored at 0° for 0, 3 and 6weeks were analyzed their microfloral composition according to the determinative schemes shown in Figures 1 and 2.
The flora of pre-irradiated fresh fish fillets and those of non-irradiated-food preservative treated fillets are shown in Table 1 and 3 respectively. The great majority of survivingand growing organisms in the control and drug treated fillets during storage was Pseadomonas, Aficrococci and other Gram-positive organism in the CTC and FF treated samples, declined during storage.
As can be seen in Table 2, Gram-positive organisms, especially yeast become predominant after irradiation with or without food preservatives among the microflora of halibut fillets especially the organisms become predominant in the flora of CTC or FF treated fillets during refrigerated storage.
To the contrary, as can be seen in Table 4, the irradiated flora of tuna fillets of nontreated with drug consisted of Enterobaoteriaceae, Micrococcus and Microbacterium-Corynebacterium, and during low temperature storage, Pseudomonas and yeast were dominated. It was obvious that the pretreatment with either CTC or FF changed the microflora of surviving and growing organism in the test fillets during storage, however, as far as the present study is concerned it was rather difficult to evaluate the composition of microflora quantitatively due to shortage in number of the isolates.
In Table 5, some characters Psedomonas isolates associating with putrofying activity was illustrated.

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To obtain the basic aspect on the qualitative change of fish flesh in radiation preservation, effects of gamma irradiation on some properties of fish actomyosin were investigated. As a remarkable change from sol to gel of carp actomyosin solution during irradiation was observed, the gel formation and its specificity under various conditions were described in this paper.
The results obtained are as follows:
1) The gelation was observed organoleptically in a higher concentration of actomyosin than 0.3 mg protein nitrogen/ml and above the irradiation dose of 8× 10⁴R. (Table 1)
2) The concentration of KCl in actomyosin solution had a close relation to the gel rigidity. The highest rigidity was observed at the KCl concentration of 0.6M. (Table 2) Thus, this fact may bring an important influence on the quality of such a salt-treated flesh during irradiation.
3) The suppressing effect of dissolved oxygen on the gelation of irradiated actomyosin was observed, while N₂, H₂ and He gasses accelerated the gelation respectively. (Table 3)
4) Added oxidants such as KBrO₃ and KI0₃ accelerated to gelify, and the antioxidant, sodium D-isoascorbate restrained fairly the accelerative effect of KBrO₃ during irradiation. (Tables 4 and 6)
5) Dissolved oxygen showed also a synergistic enhancement on the gelation of irradiated actomyosin when KBrO₃ was added to the actomyosin solution. (Table 5) From the above results, it is supposed that the mechanism of gel formation by ionization and oxidation by molecular oxygen differs primarily from that of various oxidants.
6) From the differences of the, protein solubility in super-natant centrifuged, it was illustrated that a higher macromolecule of actomyosin was formed during irradiation. (Figs. 1 and 2)
7) The roles of sulfhydryl groups on the gel formation was suggested from the results of polarographic observation of protein waves. (Fig. 3)

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The “acceleration effect” of cod viscera on the formation of DMA by irradiation cleavage of TMAO and the enzymatic “acceleration factor” estimated to be involved in the tissues of cod were reported in the previous paper. On the contrary, “ inhibition effect” of fish blood was observed when it was added into cod flesh prior to irradiation.
In this paper, experiments were made using carp flesh added with TMAO and horse mackerel flesh, both possessed no or little “acceleration factor”. Irradiation on carp flesh showed an increase of the amount of DMA by addition of carp blood (Table 1). Similar results were obtained in the experiments of irradiation on the flesh of horse mackerel or carp added with horse mackerel blood (Table 2). However, carp blood added in the mixture of carp flesh and a cod pyloric coeca revealed a marked inhibition effect on the irradiation production of DMA (Table 3). These findings came to a conclusion that the effect of fish blood on the formation of DMA during irradiation was accelerative when the irradiated sample did not contain so-called “acceleration factor”, and, the “inhibition effect” of the blood exhibited only in the sample containing “acceleration factor” such as cod .flesh.
The formation in the irradiated flesh of carp or horse mackerel was also increased by addition of the blood;“acceleration effect” of cod pyl oric coeca or “inhibition effect” of carp blood was not observed in this case (Table 1, 2, 3).
Data shown in Table 4 indicated that the accelerative effect of the blood described above was not enzymatic, b ecause heat treatment on the blood of two fishes caused rather slight increase of the amount of DMA and TMA formed during irradiation.
Haemoglobin was previously reported showing the same“inhibition effect” as that of the blood. In this work, raw carp blood and a haemoglobin preparation made of carp blood, both.in equal haemoglobin concentration (4.2%), revealed about the same degree of effect on increment of the amines formed by irradiation. On the basis of the experimental results shown in Table 4 and 5, the function of the blood related to the acceleration of the irradiation formation of DMA and TMA were considered to be wholly due to activities of haemoglobin, and, some component of it which possessed large stability against heat treatment was estimated to play a major role in the function of blood.

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In spite of many efforts in the handling aboard, discoloration of frozen tuna is unavoidable and causes unprofitable market price for the fish handlers who can find out the defect only after thawing.
It is well known that meat irradiated in atmosphere undergoes a remarkable discoloration by forming metmyoglobin.
But, on the other hand, regeneration of oxymyoglobin from metmyoglobin by irradiation has also been noticed by many investigators in various kinds of meat.
The writers presumed that the regeneration of oxymyoglobin of this type might find a practical application for the color improvement of frozen tuna, since the industry has been seeking some technological solution for the discoloration.
As there has been no information available.about quantitative evaluation on the regeneration of oxymyoglobin by the irradiation, the present paper reports a preliminary part of the observations on the dose levels required to attain a desirable color generation and its possible period of retention of the color in frozen storage.
Between 0.2 Mrad and I Mrad of given dosages, the grade of color regeneration in terms of metmyoglobin percentage was about 40 percent after irradiation of a discolored tuna containing 75 percent of metmyoglobin and these were judged bright red organoleptically. However, irradiation higher than 0.2 Mrad was found not practical because of the developed off-flavor.
More important problem noticed was reversible formation of metmyoglobin in comparatively short time even underfreezing condition. Further studies shall be needed to prolong the regenerated meat color.

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Changes in digestion of γ-irradiated casein solution by trypsin, rennet, papain and pepsin were studied.Temperatures during irradiation were at 20, 0 and -78°C.
Amount of free tyrosine (Tyr) and non-protein nitrogen (NPN) which had been degraded from casein, increased progressively during irradiation.
Four enzymes liberated highly less amounts of Tyr and NPN from casein irradiated at 20 and 0°C up to 2.4 Mrads than from non-irradiated ones. After irradiation at -78°C liberation of Tyr and NPN by these enzymes decreased slightlycompared with that of non-irradiated casein. There were less amounts of Tyr and NPN liberated after irradiation with dose of 2.4 Mrads at 0°C than those at 20°C.

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Pasteurized effect of γ-ray on wiener sausage, which is much consumed in Japan, was investigated to extend its shelflife.
1. Two strains of Staphylococcus and one strain of Diplococcus were irradiated with 0.5 Mrad dose. Only Diplococcuswas not killed, but it did not increased during storage for 24 hours at 5-8°C after irradiation.
2. The Staphylococcus contaminated with each kind of germs above mentioned on the surface of wiener sausage, were not destroyed, even though they were irradiated with the same dose. The radiosensitivity of Staphylococcus may be different from various cultures.
3. It was recognized that the terms of shelf-life of the irradiated wieners were extended about three times longer than that of unirradiated one.
4. Nineteen strains of bacteria, isolated from meat products, were cultured in liquid medium and irradiated. Four strains of them were not destroyed with irradiation of 0.5 Mrad dose, whereas the other bacteria were killed completely.But they did not grow under the low-temperature, so that they will not bedetectable in wieners hold at 5-8°C after irradiation.

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In food irradiation, water-soluble food constituents undergo the attack of e^-_aq and OH at the neutral region.
Reaction rate constants of some food constituents with e^-_aq were measured by competition method using nitrous oxide according to Scholes and Simic and those with OH were measured by a competition method using ³H-formate newly deviced as described in the following part:
Radioactivity of water increased linearly with dose when aqueous solution of ³H-formarte (2μCi/ml and 2×10^-3M) -was irradiated with γ-rays in the presence of oxygen.
The increase of the radioactivity was reciprocally proportional to the non-labeled formate concentration where the amount of ³H-formate was kept invariable.
Addition of ferrocyanide and 2-propanol, effective OHradical scavengers, depressed the radioactivity increase to near zero.
These facts show that the abstraction of tritium from ³H-formate by OH-radicals causes the increase of the radioactivity of water.A competition method to measure relative rate constants for reactions with OH-radicals was deviced on the present results.
Some values by this method well agreed with published data as shown in Table I.

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When amino acids in aqueous solution were irradiated by ionizing radiations, radiolytic oxidation of sulphur When amino acids in aqueous solution were irradiated by ionizing radiations, radiolytic oxidation of sulphur atoms and carbon atoms of the amino acids were found to occur. The fact that the oxidation is caused initially at the sulphur atoms and finally at the carbon atoms, is worthy for food irradiation.
Mechanisms of radiolytic oxidation of sulphur and carbon atoms of amino acids and related compounds in aqueous solution are proposed in Table 1 and 2, from the experimental resultson methionine and cystine.
In order to solve the mechanisms of radiolytic oxidations, a rapid flow method of e.s.r. spectroscopy was applied using a ferrous hydrogen peroxide reagent for detection of the radicals which were produced in the aqueous solutions of amino acids and related compounds by gamma irradiation. Structures and characteristics of the obtainable radicals are summarized in Table 3, 4, 5.
The results mentioned above are of importance for food irradiation.and carbon atoms of the amino acids were found to occur. The fact that the oxidation is caused initially at the sulphur atoms and finally at the carbon atoms, is worthy for food irradiation.
Mechanisms of radiolytic oxidation of sulphur and carbon atoms of amino acids and related compounds in aqueous solution are proposed in Table 1 and 2, from the experimental resultson methionine and cystine.
In order to solve the mechanisms of radiolytic oxidations, a rapid flow method of e.s.r. spectroscopy was applied using a ferrous hydrogen peroxide reagent for detection of the radicals which were produced in the aqueous solutions of amino acids and related compounds by gamma irradiation. Structures and characteristics of the obtainable radicals are summarized in Table 3, 4, 5.
The results mentioned above are of importance for food irradiation.

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The UV transmission curves of high molecular films wereaffected by γ-irradiation.
(i) At dose of 1×10⁶ R, no significant effects no filmswere observed.At dose of 7×10⁶ R, the UV transmissioncurves of pure cellophane, polyvinylalcohol, polyethylene, polypropylene, polyvinyl chloride and polycarbonate changedtheir shapes and patterns, whereas those of polystyrene andpolyester remained unchanged. (Fig.1-7)
(ii) Byγirradiation, some of the films browned, andmoreover, the tints of color gradually changed with thelapse of time after irradiation.
The UV transmission curves of polvvinvlidene-chlorideand polyvinyl chloride, irradiated at the dose of 4.5×10⁶ R, were shifted slowly downwards, indicating further decomposition. (Fig. 8, 9)
On the contrary, the UV curve of irradiated polycarbonatewas shifted downwards for a time, and then upwards, indicating restoration of chemical status of the films.
(iii) At the dose of 1×10⁷ R, the progressive changesin the UV curves of polyvinylidene chloride (Fig. 12) andpolycarbonate (Fig. 13) were more remarkable.
The UV curves of irradiated and colored glass plates, probably containing free radicals, also were shiftedupwards during storage. (Fig. 14)

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A method for taking multi-colored overall picture of dose distribution in the radiation field by means of color radiography was proposed and denominated as “Color radiofieldgraphy” by the authors. Sentitizers suitable for this object were made of agar-gel stained with indigo carmine, naphthol yellow and tetrazolium red. These sentitizers were changed their color according to irradiation doses from green to white, yellow, red, and reddish purple. By setting this sentitizer in the radiation field of electron beams, gamma rays or x-rays, multi-colored picture of the radiation field was easily taken without developing process. By this method so many inadequate locations for irradiation by common irradiators were easily found. Moreover, many interesting informations were obtained by this method, e.g., pictures of x-rays field of higher energy resembling the form of ballistics wave, and not negligible difference in the irradiation effects between the center and the periphery of the irradiated material of any thickness. The latter effect was observed not only in the neighbour of the surface faced to the air but also in the vicinity of the barrier part of different density inside the irradiated material. This effect which we call “Rand effect” or “Barrier effect” was observed even in the ir-radiated thinner film.

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The soybean powder which is a protein-rich material inmanufacturing some processed foods is mostly contaminatedwith various types of microorganisms including appreciablenumbers of heat-resistant cells. In this study, effects of⁶⁰Co gamma irradiation on defatted soybean powder samplesobtained from the hexane-extraction process as a by-productwere investigated. The results are as follows: (1) Allsamples were sterilized with 8×10⁵rads and survivors weredecreased to the level of 10²cells/g by 5×10⁵rads. (2) As shown in Figs.1 and 2, two-component-type survivalcurves were obtained with both the soybean powder and thecell suspension of an isolated bacterium. D₁₀values areindicated in the figures. (3) No significant deteriorativeeffect of irradiation (less than 1 Mrads) on the colour andodour of the sample while viable numbers of microorganismswere suppressed during storage after irradiation. (4) Theα-amylase activity of the soybean powder was not decreased with doses up to 2 Mrads

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Radiation effects on parathion, phenyl mercuric acetate and methyl mercuric chloride (which is considered causative agent for so-called “ Minamata disease ”) in the aqueous solution were observed.
Parathion was found to be easily detoxicated by gamma irradiation.
Phenyl mercuric acetate in the solutions of high concentration developed pale-brown flock and precipitate by irradiation, which could be rapidly sedimented by the use of flocculation and coagulation with coagulant such asalum. The mercury content in the supernatant of the treated water decreased with increasing dose.
Irradiated methyl mercuric chloride solutions developed white precipitate when the concentration of the solutions higher than 100 ppm. The mercury content of the super-natant of the solution treated by irradiation and coagulation decreased with increasing dose. By radiolysis, organic mercury compounds were turned to inorganic compounds.

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The applicability of radiopasteurization method to fermentation media consisted mainly of molasses was investigated. It was found that γ-radiation had an excellent pasteurization effect on the fermentation media and an increasing effect of ethanol fermentation rate and ethanol yield on the irradiated mashes. Per cent survivals in molasses decreased to ca. 70% with heating at 80°C for 30 min, toca, 10% with irradiation by 3.0×10⁵R and to ca. 1% by 6.0×10⁵R (Table 2). The irradiated mashes were suitable for media of the “starter”, since the rate and the degree of the growth ofSaccharornyces cerevisiae in irradiated mashes did not differ from the growthin in heat-pasteurized mashes (Fig. 2). In case of the molasses mashes added nitrogen sources, ethanol fermentation rate and yield in irradiated mashes were larger than those in heated mashes (Figs. 3 and 4). Besides. a 14% difference was seen between fermentation yield in mashes irradiated by 3.0×10⁵R and that in mashes heated at 80°C when no nitrogen sources were added to the mashes (Fig. 4). In the dose range between 1.0×10⁵and9.5×10⁵R the concentrations of total sugar and direct reducing sugar, pH (Fig. 5), and optical density of molasses were little affected by radiation.

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Sliced and dehydrated carrot was irradiated with 1 Mev of cathode ray and investigated with their rehydration rate, swelling velocity, changes of hardness and pectic substances.
(1), The hardness of irradiated dried carrot after rehydration was eponentially reduced with increased dose level. (Fig. 2) Water absorption rate of irradiated dried carrot was accelerated by radiation and the time required for 7g of water absorption into the 1g of irradiated sample at 1.7 Mrad was about the half withnon-irradiated carrot. (Fig.3)
(2).The changes of swelling velocity were analyzed both with irradiated dried carrot at the dose of 1.7 Mrad and with non-irradiated one using an apparatus (Fig.1) for the measurement of the total volume decrease.Dried carrot was rehydrated in the water and the decrease of total volume was determined in every minutes. (Fig.4, 5, 6) The rate of total volume decrease was accelerated and the total reducedvolume was increased remarkably by radiation at the dose of 1.3 Mrad, but the rate of water absorption was not accelerated so much under the same conditions. (Fig.7) These results suggest the altered swelling mechanism in the irradiated dried carrot.the fact ofdecrease in the total volume and weight of absorbed water, it may indicate that.a more greater combination or chemical reaction between water molecules and the micelles takes place in theirradiated dried carrot than in the non-irradiated one. (Fig.8) These reactions cause remarkable decrease of total volume but little acceleration of the swelling of the carrot due to absorbed water.
(3). In dried carrot, the radiation treatment caused the reduction of total pectic substances and protopectin and the slight increase of the pectate and the pectin with the increased dose level.(Fig.9)
(4).Statistical analysis of the organoleptic tests after the rehydration showe that the significant differencesin flavor and taste were not detected between the non-irradiated dried carrot and the irradiated oneup to the dose of 1.7 Mrad. (Table 1) Irradiated dried carrot at the doses of 0.25 and 1.0 Mrad required shorter cooking time of 2/3 and 1/2 respectively than that of non-irradiated carrot.

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The suitability of ionizing radiation as means of regulating the fruit ripening has been investigated. There are also a few reports on the removal of the astringency in Kaki fruit by gamma radiation. The present paper reports the differences among the varieties and the effects the dose levels on the removal of the astringency by gamma radiation, and its physiological changes was also investigated.
The varieties of ‘Hiratanenashi’, ‘lMiyazakimukaku’ and ‘Atago’ were primarily used in the experiments, and two varieties of ‘Yokono’ and ‘Hagakushi’, were used in part. Tie fruits were irradiated at the doses from 1.5×10⁵R to 4.0×10⁶R by gamma rays from Co 60 at the dose rate of 2.5×10⁵ R/h.The temperature durimg the storage was at 20°C or at room temperature for the storage of ‘Yokono’ and ‘Hagakushi’ fruits .
With ‘Hiratanenashi’ variety, the fruits irradiated at the doses less than 1.5×10⁵R had no change in the appearance immediately after irradiation. However, the fruits irradiated at the dose of 4.0×10⁶R lot became very soft and dark-brawn in color, and they had almost no-astringency. The fruits irradiated at the doses of 1.5×10⁵R and 2.5×10⁵R ripened 3 to 5 days after irradiation, accomparried by the removal of the astringency (Fig.1).However, the following is of special interest in this experiment. The softening of the flesh and the astringent removal during the storage were less at the doses of 1.0×10⁶R than at the doses of 1.5×10⁵R, 2.5×10⁵R and 4.0×10⁶R, though these changes were greater immediately after irradiation as the radiation dosage increased. Such tendency was also observed in ‘Miyazakimukaku’ and ‘Yokono’ varieties (Table 1). In ‘Atago’ variety, the flesh of the irradiated fruits softened immediately after irradiation and during the subsequent storage with increased level of the radiation dose.
The soluble tannin content rapidly decreased and the contents of acetaldehyde (Table 2) and soluble pectin increased in the irradiated fruits which became soft immediately after irradiation or during the storage. Ascorbic acid content decreased with higher dose. From the results of the separation of free amino acids by using the thin layer chromatography, the composition of amino acids appeared to be unaffected by gamma radiation (Fig.2).
The CO₂ production rates of irradiated fruits sharply and temporarily increased immediately after irradiation and gradually declined thereafter. The rates of this initial increase in CO₂ production were proportional to the dose level up to the dose of 1.0×10⁶R (Fig.3).

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The Bartlett pears at the stage of mature green were irradiated at 2.5×10⁵R, and 1.0×10⁶R with gamma rays from Co 60 at the dose rate of 2.5×10⁵R/h, and were stored at20°C.
The yellowing of the irradiated pears was delayed and was more gradual (Fig.1), the time for the transition from green to yellow was about twice as long in the fruits irradiated at the dose of 2.5×10⁵R lot.High levels of radiation doses (above 5.0×10⁵R) interfer normal coloring; the fruits at 5.0×10⁵R became only yellowish green, and the fruits at 1.0×10⁶R did not develop yellowish color.
Gamma radiation caused the softening of the tissue immediately after irradiation. The subsequent change was smaller in the irradiated fruits than that in the unirradiated ones. The decreases of protopectin and water soluble pectin were slower in the irradiated fruits than those in the unirradiated ones during the storage (Fig.2). Particularly, the flesh of the fruits at 1.0×10⁶R was mealy and atypical. The hydrolysis rate of starch in the irradiated fruits were slower than those in the unirradiated ones during the ripening (Table 1). In the fruits irradiated at the dose of 1.0×10⁶R lot, a little change in the starch content occured during the storage. The free amino acids in pears were separated by means of thin layer chromatography with silica gel G. Ten kinds of amino acids were found in each samples. The increase of proline took place in both irradiated and unirradiated fruits, but the quantitative differences of other amino acids were not observed on the chromatograms among the samples.
Though the characteristic flavor of pears was appeared at maturity of the fruits at 2.5×10⁵R but was not given in the fruits at 5.0×10⁵R and 1.0×10⁶R. The analysis of volatile substances by means of gas chromatography indicated that a large amount of volatiles was present at maturity of the fruits at 2.5×10⁵R and above this dose level the production of volatiles were considerably interfered. The production of carbon dioxide increased immediately after irradiation, but the initial increase declined rapidly thereafter. The pattern of carbon dioxide production indicated that the irradiation would delay the onset of the climacteric or would supress the climacteric rise completely. The evolution of the ethylene which is accompanied with the climacteric rise of pears was also interfered with higher doses of radiation, while the fruits irradiated at the dose of 2.5×10⁵R lot produced relatively large quantity of ethylene.

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Potato tubers were subjected to cobalt-60 gamma-ray irradiation and stored at room temperature for 10 days to 4 months. Effects of the irradiation on metabolic changes in potato tubers in response to cutting were investigated. The quantities of phenylpropanoids such as chlorogenic acid and isochlorogenic acid in the tissue increased as compared with the non-irradiated sample. Although phenylpropanoid content and activities of o-diphenol oxidase, peroxidase and phenylalanine ammonia-lyase were increased after cutting, the increases were lower in irradiated sample. On the other hand, in the dose range from 5, 000 to 12, 400 rad, the irradiated sample showed a larger defense action against the infection of the black rot fungus, Ceratocystis fimbriata than the non-irradiated sample.

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Mushroom (Psalliota bisporus), and. Shii-take (Lentimus edodes) were irradiated from tne dose of 5 to 50×10⁵ rad with γ-ray, and the changes in nucleic acid related substances were measured by chromatography with a Dowex 1×8 column.
ATP of mushroom and Shii-take disappeared at the dose of 5×10⁶rad, but ADP of those remained in as much as initial amounts (Figs. 1 and 2, Tables 1 and 2). The changes in the amounts of mononucleotides were negligible.
Preliminary experiments were made on the extractability of nucleic acid related enzymes from mushrooms. Extracted enzyme solutions from mushrooms were subjected to γ-irradiation, as .a result their ribonuclease, phosphodiesterase and DhoslDhomonoesterase activities remained moderatelyeven at a high dose of 5×10⁶ rad (Figs, 3 and 4).
It seems reasonable to consider that there is a possibility of the breakdown of nucleic acid related substances by remaining enzymes during the storage after γ-irradiation.

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5'-IMP and related 5'-nucleotides are potent flavor substances contained in some foods. Sodium salts of 5'-IMF and other 5'-nucleotides were dissolved in distilled water or buffered solution and sealed in glass ampoules under atmosphere. The samples were irradiated with a 5, 000 curie cobalt-60 source at the dose rates of 2.3×10³-3.6×10⁵ r/hr at room temperature.
The residual levels of 5'-IMP irradiated at 1.0 Mrad were 61 and 86% in distilled water and in buffer of pH 7 (Fig. 2), respectively. The decimal reduction dose at pH 7 was 17.2 Mrad. 5'-IMP was found to be more labile at pH 3 and 5 rather than at pH 7 and 9 (Fig. 3). Irradiation of 5'-IMP led to the splitting of the bond between nucleic base and ribose phosphate, resulting in the increase of hypoxanthine (Table 5 and 6).
There is a significant difference between the mode of decomposition affected by heating and by γ-irradiation.
Purine nucleotides are more stable than pyrimidine nucleotides against γ-irradiation (Table 3 and 4), but the formers are more labile than the latters against heating. Existence of sugar is protective against the destruction by γ-ray (Fig. 5) but is promotive of that by heat.

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Decoloration by gamma rays of aqueous solutions of fourteen coal-tar food dyes permitted in Japan was observed.Light green SF yellowish and new coccin were decolorized sensitively by gamma rays, but acid violet 6B and rose bengal were comparatively resistant. This tendency is different from the results obtained by exposure to daylight. Acute toxicity of the irradiated dye solutions to Japanese goldfishes was observed. The irradiated solutions of amaranth, erythrosine, new coccin, eosine, rose bengal, acid red, sunset yellow FCF, brilliant blue FCF were found to be more toxic than the unirradiated ones. For one example among them, irradiated erythrosine solution was administered to mice intraperitoneally, which resulted in an increase in toxicity as .compared with' the unirradiated solution. Hydrogen iodide was found to yield in the irradiated solution but it was not enough to interpret the toxic action of the irradiated solution.

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The effects of γ-irradiation on the enzymatic formationof characteristic odor and pungent taste in onion were investigated.It is well known that their formation dependupon the degradation of the precursor amino acid, S-alkyl-Lcysteinesulf oxide. by action of its lvase existing in onion.
When irradiated with low dose rate (5×10⁴rad per hour), the enzyme activity in the irradiated onion was notso decreasedwithin the absorbed dose of 1×10⁵rad of dosescompared with that in the unirradiated one. The enzymesolutions prepared from the onions were irradiated under thesame condition mentioned above, and the activity exhibitedthe same tendency as in case of irradiated onions. Whenan aqueous solution of the substrate (S-alkyl-L-cysteinesulfoxide) was irradiated, its decomposition was observedabove the dose of 2×10⁴rad of doses and a numher of productswere detected by ninhydrin color reaction on cellulose plate.

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One of the most important problems associated with food irradiation processing is the off-flavor development. It is considered that the major cause of off-flavor is attributed to the decomposition products of amino acids, especially of the sulfur containing amino acids.
The purpose of this paper is to describe the relationshipbetween radiolysis of amino acid and off-flavor development.Expeliments were carried about ordinary aminoacids, sulfur containing amino acids and raw fish meat.
1. Amino acid
Aqueous solutions of amino acid (glycine, alanine, valine, leucine, isoleucine, threonine, serine, glutamicacid, aspartic acid, phenylalanine, tyrosine, tryptophan, proline, methionine, cystine, cysteine and cysteic acid, 40 gamma of each per ml.) were irradiated with cobalt 60gamma ray radiation facility at 0.27 and 1.80 Mrads. Afterconcentration under reduced pressure, the sample was analyzedcolumn chromatographically using Dowex 50W X-8 ion-exchangeresin by the method of Moore and Stein.
The elution curves of alanine and aspartic acid areshown in Fig. 1 and 2.
Conclusively the radiolytic mechanisms of neutral fatty amino acid, acidic amino acid, sulfur containing amino acid, imino acid and aromatic amino acid weredifferentrespectively.
2. Sulfur containing amino acid
Aqueous solution of cystine (40 gamma per ml., almost the saturated solution at ordinary temperature) and of methionine, cysteine, cysteic acid and related compounds -α-amino-n-butyric acid, homo-serine- (each 200 gamma per ml.) were irradiated at 0.27 and 1.80 Mrads. The same methoddiscribed above was followed for analysis.
The radiolytic pathway of methionine (Fig. 5) wassuggested by the column chromatogram (Fig. 4). Mechanism ofradiolysis of cystine (Fig. 3) was proposed by the same reason.
As it was considered that off-flavor development fromcystine .and methionine were attributed to the intermediateproducts of oxidative decomposition, these sulfur containingamino acids were reinvestigated by irradiated by irradiationin the addition of oxidizing (potassium bromate and sodiumhypochlorite) or reducing agents (sodium hydrosulfite, pyrogallol and sodium sulfite) which promote or restrainthe radiolysis.
Radiation induced off-flavor as well as ninhydrinreacted color were less when sulfur containing amino acidswere irradiated in the presence of oxidizing agents and werecontrary when reducing agents.
3. Fish meat added oxidizing or reducing agents
Dosal meat of yellowfin tuna, Thunnus alabacares, was minced, added individually 0.1% of oxidizing or reducingagents which were used in experiment about methionine, andirradiarbed at 0.27 and 1.80 Mrads at -5°and +5°C.
Off-flavor development from fish meat was weak in thecase of addition of oxidizing agent (especially potassiumbromate), but undesirable change of color was apparently.
In the case of addition of reducing agents, off-flavordevelopment and change of color were in direct opposition.

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