Abstracts of Annual Congress of The Japan Society of Home Economics

1. IntroductionVarious sterilization technologies have been developed in last two decades in order to maintain the quality of foods. Irradiation by gamma-ray has been recognized internationally as a frequently used food technology. Heat-treatment of foods causes not only sterilization but also the decomposition of food ingredients and the degradation of their enzymatic activities. The heat-treatment promotes radical decay reaction by re-combination. Electron spin resonance (ESR) spectroscopy has been applied as a method of detecting the irradiated foods all over the world. In fact, it has been established as a standard detection method (European Committee for Standardization) in Europe union (EU) ¹⁾. ESR is a non-destructive standard method that enables a quick measurement for radicals. ESR method utilizes comparatively long-living radicals in bone and cellulose induced by gamma-ray irradiation. However, preservation conditions may affect ESR measurement of radicals ²⁾.
In the present study, we analyzed the radical behavior of the irradiated black pepper, a typical spice under the heat-treatment process by ESR. The comparison between the heated and the unheated pepper enables to reveal the radical change.
2. Experiment
The pepper specimen in the present study was commercially available black pepper in Japan, bottled in glass (18 g) and stored at room temperature. Irradiation was carried out at Japan Atomic Energy Research Institute (Takasaki research institute) at the room temperature (ca, 300K). We selected the dose level, i.e., 10kGy, 20kGy, 30kGy and 50kGy as compared to the FAO / IAEA / WHO standard. Fifteen specimens of the black pepper were prepared with the amount of 300mg as weighed in the aluminum pan. They were heated for various intervals from 1 to 15 minutes in an electric oven which was preheated for 15 min and remained at 180˚C. The specimen was sealed in the ESR sample tube (Eiko) with the amount of 300 mg. ESR measurements were carried out using the two ESR spectrometers (JEOL, JES-FE1XG and JES-FA200). All the ESR spectra were recorded at the X-band (9.3 GHz).
3. Results and discussionThe peak intensity of the side peaks was fairly constant during the heat-treatment for 0 - 2 minutes. They decayed exponentially after the heat-treatment beyond 2 min. We estimated the parameters by the application of the non-linear least squares method. The estimation resulted in 1.8 min for the time constant for the thermal decay process.
Conclusions1) The peak intensity of the side-peaks as appeared upon irradiation was a quite different from that of organic free radicals by heating. These signals decreased exponentially by heating-treatment. The ESR signal of the pepper heated for more than 10 minutes was essentially the same as that before the irradiation.
2) In order to evaluate the radical decay during heating, we defined a time-dependent master equation. Using the solution, we could evaluate the decay time constant through the nonlinear least squares fitting method.
References
1. EN1787 (1996) 2. Ukai, M., Shimoyama, Y., RADIOISOTOPES, 51, 501-504(2002)

View full abstract

Show abstractHide abstract

1. Introduction
Gamma-ray irradiation is now internationally recognized as an effective sterilization method. It has also been noted that sterilization through gamma-radiation is effective, and its safety has been proved for approved irradiation levels, such as 10 kGy (Joint FAO/IAEA/WHO 1981). However there is public apprehension that the production of radicals by ionization and the generation of unknown substances in foods may be harmful to the human body. The ionization by irradiation induces radicals in foods. Electron spin resonance (ESR) spectroscopy has long been applied to detect the radiation-induced radicals in foods. In previous studies (Ukai 2002; 2003), we have reported that heat-treatment of irradiated foods causes the evolution of free radicals. In this study, we analyzed the time-dependent phenomena of the radical evolution. We established a physical theory as based on the first-order differential equation, which is a conventional way for the time dependent phenomena. Attempts have been made to characterize the order and the multiplicity of reaction scheme and time constants of the radical evolution.
2.Experiment
The sample was black pepper commercially available in Japan. Irradiation was carried out at the Japan Atomic Energy Research Institute (Takasaki Research Institute). We selected the dose level to be 50 kGy. Fifteen sample lots of the black pepper were prepared 300 mg by weighting in aluminum pans. They were heated for various intervals in an electric oven remained at 180ºC. Each sample (300 mg) was sealed in the EPR sample tube (Supracil; Eiko). ESR measurements were carried out using an ESR spectrometer (JEOL; model JES-FE1XG). All the ESR spectra were recorded at the X-band (9.3 GHz).
3. Results and discussion
We observed that the ESR spectrum of the irradiated black pepper was composed of 4 components signals. The first one is a sharp signal at g = 2.0, which is due to the organic free radical. We estimated g-value = 2.002 and the line width 8 gauss of the signal. The second one consists of a sextet pattern centered at g = 2.0, which originates from the hyperfine lines of Mn²⁺. The third one is a signal of g = 4.0, which is identified as Fe³⁺. These three spectral components were always observable in the ESR spectra of pepper irrespective of before and after irradiation. The fourth signal is typical for the spectrum of irradiated pepper. The peak- to-peak intensity of the organic free radical increased by heating for 5 to 15 min as compared with that before heating. The intensity value from the samples as heated beyond 10 min leveled off at the certain value. We applied the nonlinear least squares fitting method onto the radical evolution. The evolution data for the irradiated black pepper were successfully fitted by a single exponential function. In the case of the irradiated black pepper, the best-fit curve yielded 4.2 min for the evolution process during heating for 0 - 15 min. Employment of the nonlinear least squares method needed for the memory size by ten times that makes possible the highly reliable numerical calculation.
References
Joint FAO/IAEA/WHO. 1981 Expert Committee on Wholesomeness of Irradiated Food. WHO, Geneva. No659
Ukai M. et al. 2002. Radioisotopes 51: 501_-_504.
Ukai M. et al. 2003. Appl Magn Reson 24: 1_-_11.

View full abstract

Register with J-STAGE for free!