Detection of free radicals in γ-irradiated soybean paste by electron spin resonance spectroscopy

Using electron paramagnetic resonance (EPR) spectroscopy, the levels of carbon-centered radicals in retail samples of isolated soy protein (ISP), soy protein concentrate (SPC), and powdered soy milk were estimated to contain from 6.12 x 10(14) to 1.98 x 10(15) spins/g of soy product. Roasted soy nuts contained about 5.70 x 10(15) spins/g. The peak to peak line width of the carbon-centered radicals from soy nuts was about 10 gauss, whereas ISP samples with a similar peak height had a peak to peak line width of about 8 gauss. Retail snack bars containing ISP, SPC, and/or roasted soy nuts with a total protein content of either 13, 21, or 29% contained 5.32 x 10(14), 6.67 x 10(14), and 5.74 x 10(14) spins/g of snack bar, respectively. Levels of carbon-centered radicals in newly prepared samples of ISP were much lower than levels in the retail soy protein products and levels previously reported for commercial ISP and laboratory ISP samples. The levels of radicals in ISP samples increased over a 12-25 week period of storage in the dark at 22 degrees C and exposed to air from about 8.00 x 10(13) spins/g immediately after preparation to 9.95 x 10(14) spins/g of ISP. Storing the ISP samples under nitrogen at 22 degrees C greatly reduced the increase in radical content, whereas storing the ISP in 99.9% oxygen at 40 degrees C accelerated the formation of stable carbon-centered radicals. ISP samples hydrated at either 22 or 92 degrees C, rapidly frozen, and dried lost about 92% of the trapped radicals. The level of carbon-centered radicals in these same ISP samples immediately began to increase during subsequent storage exposed to the air and gradually returned to similar levels obtained before they were hydrated.

Section: Introductionmentioning

confidence: 99%

“…This is particularly true when one is distinguishing between nitrogen-centered and carbon-centered radicals because their g values are so close. Published g values for nitrogen-centered radicals range from 2.0022 to 2.0065 (2) and from 2.0041 to 2.0054 for carboncentered radicals (3)(4)(5)(6)(7)(8). Nitrogen-centered radicals exhibit a triplet pattern (4,6,9), whereas carbon-centered radicals typically exhibit a single broad peak with power saturation levels of 2-8 mW (10).…”

Section: Introductionmentioning

confidence: 99%

Effect of Storage Conditions on Carbon-Centered Radicals in Soy Protein Products

Boatright¹,

Lei²,

Jahan³

2009

“…It is very important to know what part of soybean paste these lines belong to. At the elevated temperature above 0 °C some stable radicals remained in dry sample,whereas they disappeared completely in wet samples (18).…”

Section: Resultsmentioning

confidence: 94%

“…Therefore the molecule number (N st ) of 0.005 g of CuSO 4 5H 2 O was calculated to 1.2 × 10 19 and the signal area (S st ) of CuSO 4 5H 2 O was 2.055 × 10 9 . For example, when the signal area (S) of 1 g of WSP at 5 kGy was 9.11 × 10 8 , the number of paramagnetic particles (N), and thus the radical concentration (C), was calculated to 5.32 × 10 18 .…”

Section: Resultsmentioning

confidence: 99%

Electron Spin Resonance Studies of Free Radicals in γ-Irradiated Soybean Paste

Lee¹,

Volkov²,

Lee³

2001

Self Cite

Free radicals in gamma-irradiated soybean paste were investigated by electron spin resonance (ESR) spectroscopy to determine the effect of temperature (77-296 K) and moisture content (1-54%) of samples irradiated at high dose (1-40 kGy). The samples were kept in liquid nitrogen (77 K) during irradiation and subsequent ESR measurements. The spectra shown at 77 K consisted of the hydrogen atom lines at low and high field and complicated symmetric spectrum. By increasing the microwave power, the line shape of ESR spectra altered, which indicated the detection of different paramagnetic centers at different microwave powers. In saturation curves, it was possible to select four types of spectra components which were different in their relaxation times. By the different irradiation doses, the change in free radical concentration showed a curvilinearly increasing relationship with irradiation dose in wet samples, whereas a proportional relationship was observed with dried samples. This might indicate that the indirect process of free radical formation was involved with the existence of free water radicals in the wet samples.

“…Using the combined techniques of on-line high-performance liquid chromatography/electron spin resonance and mass spectrometry (LC/ESR and LC/MS), Qian et al (4,5) identified spin trapped lipid-derived carbon-centered radicals formed in linoleic acid peroxidation and the reactions of two ω-6 polyunsaturated fatty acids (linoleic and arachidonic acids) with soybean lipoxygenase in the presence of R-[4-pyridyl 1-oxide]-N-t-butyl nitrone. Polat and Korkmaz (10) used ESR spectroscopy to study kinetics of radiation-induced free radical and Mn 2+ signals in γ-irradiated ground soybeans at a temper-ature range of 130-400 K. Lee et al (11,12) investigated free radicals in γ-irradiated soybean paste by ESR spectroscopy and compared it with those of soybean protein isolate and soybean oil to examine the influences of irradiation dose, moisture content, and heating after irradiation of the free radical concentration and species.…”

Section: Introductionmentioning

confidence: 99%

Detection of Free Radical Transfer in Lipoxygenase I-B-Catalyzed Linoleic Acid−Soybean Protein Interaction by Electron Spin Resonance Spectroscopy (ESR)

Huang

Hua

et al. 2006

Effects of lipoxygenase I-B (LOX)-catalyzed oxidation of linoleic acid on soybean proteins was evaluated by electron spin resonance (ESR) and fluorescence spectroscopy in different model systems in the presence or absence of antioxidants. A strong central singlet signal was detected by ESR spectroscopy and identified as the carbon radical (g value range 2.0041-2.0054). A downfield shoulder attributed to the sulfur radical (g value 2.019-2.028) was also observed. The changes in soybean proteins were accompanied by an increase in fluorescence, indicating the formation of cross-links. Natural antioxidants such as ascorbic acid and alpha-tocopherol as well as synthetic antioxidants butyl hydroxytoluene (BHT) inhibited the development of both the free radical signal and the fluorescence when added to soybean proteins prior to incubation with linoleic acid and lipoxygenase I-B; the central singlet signal attributed to the carbon radical was reduced by 35-65%. This paper clearly indicates direct free radical transfer from oxidizing linoleic acid catalyzed by LOX to soybean proteins.