E. Cruz–Zaragozaa, S. Guzmána, F. Brownb, V. Chernovc, and M. Barboza–Floresc
a Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Apartado Postal 70–543, México DF, 04510, México, e–mail: cruz@nucleares.unam.mx
b Departamento de Investigación en Polímeros y Materiales de la Universidad de Sonora, Apartado Postal 130, Hermosillo, Sonora, 83000 México.
c Departamento de Investigación en Física, Universidad de Sonora, Apartado Postal 5–088, Hermosillo, Sonora, 83190, México.
Recibido el 10 de marzo de 2010
Aceptado el 31 de agosto de 2010
Abstract
Food processed by ionizing irradiation is a safe technology and has been recognized by the FAO/WHO Codex Alimentarius Commission. It is an excellent method to prevent food spoilage and foodborne diseases by inhibiting the growth of microorganisms and slowing down ripening. The widespread use of food irradiation treatments that include spices, dry vegetables, grains and fruits make relevant the developing of methods for identification and analyses of foodstuffs processed by irradiation. The present work focuses on the thermoluminescence property of Mexican Roselle flower previously irradiated for detection purposes. The polymineral content of irradiated commercial Roselle flower (Hibiscus sabdariffa L.) was extracted and analyzed by thermoluminescence (TL). The X –ray diffraction analyses showed that quartz and albite composition of the polymineral fraction. Different grain sizes; 10, 53, 74 and 149 μm, were selected for the TL analyses. The TL glow curves depended on the grain sizes. The glow curves depicted two peaks around 92 and 120°C. The first peak was ascribed to quartz and the broad part of the glow curves (120–250°C) seems to correspond to the albite. Because the complex structure of the TL glow curves from polyminerals the kinetic parameters were calculated by a fitting process using a deconvolution method based on a non–linear least–squares Levenberg–Maquart. The values ofthe activation energy were found to be at 0.79–1.05 eV and 0.79–1.04 for 53 μm and 250 μm, respectively. The TL properties ofthe samples were determined including dose response, reproducibly, fading and UV light bleaching.
Keywords: Food irradiation; Roselle flower (Hibiscus sabdariffa L.); polyminerals; kinetics parameters.
Resumen
El proceso por radiación es una alternativa tecnológica reconocida por la FAO/WHO Codex Alimentarius Comisión, conveniente para desinfectar alimentos y lograr la seguridad de los consumidores ante el aumento de enfermedades transmitidas por los mismos alimentos en el mundo. Sin embargo, es necesario desarrollar métodos que logren identificar y analizar propiedades de los alimentos expuestos a radiación ionizante. El presente artículo esta enfocado al estudio de las propiedades termoluminescentes (TL) de la flor de Jamaica Mexicana para propósitos de detectar tratamientos con radiación ionizante. Se analizaron por termoluminiscencia la fracción polimineral de la flor de Jamaica comercial (Hibiscus sabdariffa L.) de muestras irradiadas. El análisis por difracción de rayos X (DRX) mostró que la fracción polimineral estaba compuesta de cuarzo y albita. Se eligieron diferentes tamaños de grano; 10, 53, 75 y 149 μm para el análisis TL. Las curvas de brillo muestran que la emisión TL depende del tamaño de grano. Las curvas de brillo muestran dos picos principales alrededor de 92 y 120°C. El primero esta asociado al cuarzo, y la parte ancha de las curvas de brillo (120–250°C) parece que corresponde a la albita que también está presente en las muestras de Jamaica. El método Tm–Tstop mostró que las curvas de brillo de la flor de Jamaica contiene ocho picos de brillo (100–250°C). Debido a la complejidad de la estructura de las curvas de brillo a diferentes dosis gamma, los parámetros cinéticos se calcularon mediante un proceso de aproximación usando un método de deconvolución basado en mínimos cuadrados no–lineales Levenberg–Maquart. Los valores de la energía de activación referidos a las trampas en la fracción polimineral estuvieron entre 0.79–1.05 eV para 53 μm y 0.79–1.04 para 250 μm, respectivamente. Se encontraron cinéticas de primer y segundo orden. Se evaluaron también las propiedades TL; dosis–respuesta, reproducibilidad de las señales, también el fading y pérdida de TL después de exponerlas a luz UV.
Descriptores: Alimentos irradiados; Hibiscus sabdariffa L.; poliminerales; parámetros cinéticos.
PACS: 78.60.Kn; 83.80.Ya; 78.55.Hx
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Acknowledgements
This work has been funded by the DGAPA–UNAM project IN121109. The authors are grateful to Oficinas de Intercambio Academico UNAM–Universidad de Sonora, México. The financial support from CONACyT (México) grants nos. 83536 and 82765, and SEP (México) is greatly acknowledged Thanks also to Francisco García and Benjamin Leal for irradiation samples.
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