EPR study on non- and gamma-irradiated herbal pills
Introduction
Gamma-irradiation is established as an effective non-contact technique for the sterilization of foodstuffs, drugs and medical devices. One of the main advantages of the process is the opportunity for sterilization of the products even in their final packages (Basly et al., 1998). However, this process needs a strict control. In this respect Electron Paramagnetic Resonance (EPR) spectroscopy is the leading method for identification of irradiated foodstuffs. Free radicals formed on gamma sterilization of vegetable products have been intensively investigated by EPR in order to prove previous radiation treatment (Raffi et al., 2000, Delincee and Soika, 2002, Polovka et al., 2007, Ukai et al., 2008, Yordanov and Aleksieva, 2004, Yordanov et al., 2005, Yordanov et al., 2009). Identification of irradiated herbs and spices is based on the detection of a characteristic pair of “satellite EPR lines” due to γ-induced cellulose free radicals. In addition to “cellulose-like” signal, EPR spectrum of carbohydrate free radicals may also be recorded after irradiation (Franco et al., 2004). In some cases only asymmetric singlet EPR line, which is indistinguishable from the naturally present signal even in Q-band (Yordanov and Aleksieva, 2004), can be recorded after irradiation. On thermal processing (Yordanov and Gancheva, 2000, Raffi et al., 2000) or partial saturation (Yordanov et al., 2005), these EPR signals can also be used for identification of previous radiation treatment (Yordanov et al., 2005).
High-energy ionizing radiation is also focused on drugs that cannot be sterilized by conventional methods because of their thermo-sensitivity. Active ingredients may be irradiated alone, but often in mixtures with a lot of excipients as different saccharides and other products, which contribute to the final complex EPR spectra (Raffi et al., 2002). The sterilization dose of pharmaceuticals depends on the initial microbiological spoilage (bioburden) and on the microorganisms' radio-sensitivity (Engalytcheff et al., 2004, Gibella et al., 2000). From this point of view the process is important for highly bioburden products available in natural sources. In the herbal products, which are the natural alternative to synthetic drugs, it is not possible to predict the radiation effects and stabilities of radicals in similar compounds, as even minor changes in molecular structure can have a significant influence on EPR spectrum (Ambroz et al., 2000).
As a continuation of our studies on the EPR spectra of dry medical herbs before and after gamma-irradiation (Yordanov et al., 2009), in the present paper we report our results obtained on pills, prepared by herbs.
Section snippets
Samples
The pills of medical herbs containing their following parts were investigated:
Blossoms of marigold (Calendula officinalis L.)
Whole upper part of yarrow (Achillea millefolium L.), tutsan (Hypericum perforatum L.) and thyme (Thymus serpillorum).
Leaves and stalks of hawthorn (Crataegus monogyna Jacq.) and common balm (Melissa officinalis)
Leaves of nettle (Ultica Dioica L.)
They all were obtained from specialized pharmacy shops for medical herbs. In all of them the producers declare the presence of
EPR spectra before irradiation
Before irradiation all samples of herbal pills (Fig. 1) exhibit only one relatively weak singlet EPR signal with g=2.0048±0.0005, which is equal to that observed in dry herbs and spices. It is attributed to semiquinone free radicals produced by oxidation of polyphenolic compounds present in plants (Jezierski et al., 2002) or lignin (Maloney et al., 1992). No spectra of the excipients added to the pills were recorded. The only substance from which it was possible to expect EPR spectrum before
Conclusions
The obtained EPR spectra of gamma-irradiated herbal pills are complex mainly due to the excipients overlapped with the signals of the herb. In view of this it is difficult to make definite conclusions about the nature of the induced paramagnetic species, but in any case they are not typical for the herb itself and may be used for identification of previous radiation processing. Thus, independent of the excipients nature, the recorded specific EPR spectra can be considered as unambiguous
Acknowledgment
The “National Science Fund” (Project TK-X-1604/06) is gratefully acknowledged for financial support
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