title: Thermally stimulated luminescence in powdered soy proteins.
abstract: Heating powder isolated soy proteins (ISPs) in a N₂ environment produced thermally stimulated luminescence (TSL), in 2 major temperature regions, 50 to 250°C (region R1) and 250 to 350°C (region R2). In soy protein 7S fraction, strong TSL was detected in both regions with glow peak maximum (T(m)) at 150 ± 15°C and at 300 ± 10°C. Two additional satellite or shoulder peaks were detected from the ISP and 7S protein fraction within region R1 at T(m) = 90°C and T(m) = 210°C. The soy protein 11S fraction produced a broad, poorly defined TSL peak in the low-temperature region. Electron paramagnetic resonance spectroscopy data from the control ISP sample, deuterium sulfide-treated ISP, ISP stored in either N₂ or O₂, and defatted soy flour, indicated that the trapped radicals present in ISP is associated with the production of the primary TSL peak at 150 ± 15°C. Activation energies required to release the trapped charges (for luminescence to occur) are approximately 0.70, 0.78, 1.50, and 1.8 eV for TSL at Tm = 100, 150, 200, and 300°C, respectively. The reaction mechanism that leads to the release of the trapped charges for TSL to occur followed a mixed order kinetic, between 1.5 and 1.8. The frequency factor varied between 10⁷/s and 10¹⁷/s.
authors.affiliation: Dept. of Physics, Univ. of Memphis, 216 Manning Hall, Memphis, TN 38152, U.S.A.
authors.forename: Dereje
authors.initials: D
authors.lastname: Abdi
authors.forename: Muhammad S
authors.initials: MS
authors.lastname: Jahan
authors.forename: William L
authors.initials: WL
authors.lastname: Boatright
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Walters
authors.forename: Qingxin
authors.initials: Q
authors.lastname: Lei
mesh_terms: D003080:Cold Temperature; D004578:Electron Spin Resonance Spectroscopy; D006358:Hot Temperature; D049449:Luminescence; D011208:Powders; D030262:Soybean Proteins / Q000737:chemistry*; D013025:Glycine max / Q000737:chemistry
chemical_list: D011208:Powders; D030262:Soybean Proteins
keywords: electron paramagnetic resonance spectroscopy; free-radicals; soy protein; thermally stimulated luminescence