Since γ-rays and X-rays can penetrate foods and materials, fresh raw bovine livers can be sterilized without heating after packaging. In the previous study, radicals in the livers irradiated in chilled condition were detected by using electron spin resonance spectroscopy (ESR). However, γ-irradiation of the bovine livers might be carried out in frozen condition. In this study, the livers irradiated in dry-ice were investigated for detection of radicals by using various preparations of ESR specimens. The bovine livers stuffed in straws were irradiated and measured with ESR. The existence of some dose-responsible peaks was found on differential spectra after spectra of the straw itself were subtracted. On the other hand, direct measurements of the frozen bovine livers showed a main peak and two side peaks, resulting almost straight dose-responsible lines. ESR spectra of freeze-dried powders from the livers showed a dose-responsible shoulder peak, but the side peaks disappeared. To confirm whether the radicals exist or not in the livers that were stored in the freezer for 7 days, specimens of the livers were prepared by thawing in tap water. The results indicated that the dose-responsible side peaks were still observable in the livers. In conclusion, ESR can be used as the detection method of the raw bovine livers which were irradiated in frozen condition. ESR method at liquid nitrogen temperature is suitable for the screening of the irradiated bovine livers because of its quick and easy sample preparation.

Soybeans are an inexpensive and nutritious food with strong radical-scavenging activity, believed to reduce the risk of developing diseases associated with the generation of reactive oxygen species and inhibit the progression of such diseases. Although gamma irradiation of soybeans improves their physical characteristics without adversely affecting flavor, the specific radical-scavenging activity of irradiated soybeans has not been well studied. Here, the scavenging activity of soybean water extracts for individual radical species was investigated by electron spin resonance (ESR) spin trapping. Singlet oxygen-scavenging activity increased, whereas superoxide radical-scavenging activity decreased with increasing radiation dose; however, the hydroxyl and alkoxyl radical-scavenging activity of irradiated and non-irradiated soybeans did not differ significantly. The oxygen-radical absorbance capacity of irradiated and non-irradiated soybeans also did not differ significantly. Our findings demonstrate that gamma-irradiation affects the superoxide radical and singlet oxygen-scavenging activity of soybean water extracts.

2-Alkylcyclobutanones(ACBs), such as 2-dodecylcyclobutanone(DCB) and 2-tetradecylcylobutanone(TCB) are specific products in the irradiated lipid. Thus, DCB and TCB are suitable for indicators of the irradiation history of food. We previously reported DCB and TCB concentrations in irradiated retort pouch Gyudon topping (instant Gyudon mixes which were made from a beef, onion and soy sauce and could be preserved for a long term at room temperature) after storage for one year. Here, we have evaluated the stability of ACBs preserved in irradiated retort pouch Gyudon topping at room temperature for three years.

Although interfering peaks were detected frequently after the storage at room temperature, it was possible for the detection of the irradiation history and there was no apparent decrease of ACBs concentrations in comparison with the one year storage after irradiation. These results concluded that DCB and TCB formed in retort pouch would be stable at room temperature for three years.