INVESTIGADORES
LAGORIO MarÍa Gabriela
congresos y reuniones científicas
Título:
Spectroscopic Characterization of Origanum vulgare leaves. Development of Non-destructive Methods for Quality Assessment
Autor/es:
MENDES NOVO, J.; ANALÍA IRIEL; M. GABRIELA LAGORIO
Lugar:
Córdoba
Reunión:
Encuentro; XI Encuentro Latinoamericano de Fotoquímica y Fotobiología, ELAFOT; 2012
Institución organizadora:
Universidad Nacional de Córdoba
Resumen:
Spectroscopic Characterization of Origanum vulgare leaves. Development of Non-destructive Methods for Quality Assessment Mendes de Novo, Johanna; Iriel, Analia; Lagorio, María G. Departamento de Química Inorgánica, Analítica y Química Física/ INQUIMAE. FCEyN, UBA. Buenos Aires, Argentina. Ciudad Universitaria, Pabellón 2, 1er piso, E-mail: mgl@qi.fcen.uba.ar   Origanum vulgare is a relevant herb for flavoring food and for pharmaceutical purposes used both fresh and dried. Development of non-destructive optical methodologies to infer its moisture, plant physiological state and content of active substances is of practical importance. Folowing this objective, we have studied the spectroscopic behaviour of fresh and dried leaves of this plant. UV-VIS-NIR reflectance spectroscopy, steady-state fluorescence and pulse amplitude modulated chlorophyll fluorometry (PAM) were used in this study. Spectroscopy measurements were performed on samples with different water content ranging from 90% to 6%. Reflectance values in the NIR were successfully correlated with the water content in origanum leaves, allowing non-destructive determination of humidity even through the plastic film packaging of commercial samples. Fluorescence spectra presented important emissions in the blue, in the green and in the red-far red regions. The experimental ratio of fluorescence maxima blue/green (due to phenolic compounds) remained practically constant upon leaves drying. The fluorescence ratio red/far-red (due to chlorophyll-a) increased about twice, while the ratio green/far red augmented around 4 times. The variations in these ratios have been interpreted in terms of light re-absorption processes and in relation to the enhancement of emission due to fluorophore cristalization upon drying.   The photosynthetic parameters obtained from PAM measurements declined sharply with the water content. Origanum leaves were also studied by light microscopy. Peltate trichomes and hairs have been observed at the leaf surface (Figure1). Upon excitation at 370 nm, peltate glands do not emit any fluorescence while the hairs emit blue-green fluorescence. A pronounced enhacement of the hairs emission occurs upon leaves drying. During this process a change in the hairs stucture, probably due to cristalization of fluorophores inside them, takes place. A B B A                       Figure 1. Origanum vulgare leaf surface observed by light microscopy. Magnification 40r. A . Peltate trichomes, B. Hairs   The commercial product, (dried portions of leaves and flowering tops) was also characterized spectroscopically and by light microscopy.    Acknowledgements: University of Buenos Aires (Project UBACyT 20020100100814). UBA fellowship (JMN).