3. FOOD ChEMISTRy & bIOTEChNOLOGy 3.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Food Chemistry & Biotechnology
L09 DETECTION OF SPICES’ SPICES IRRADIATION by
MODERN SPECTROSCOPIC TEChNIQuES
MARTIn POLOVKA and MILAn SUHAJ
Department of Chemistry and Food Analysis, VÚP Food
Research Institute, Priemyselná 4, P. O. Box 25, 824 75 Bratislava,
Slovak Republic,
polovka@vup.sk
Introduction
Herbs and spices are daily used condiments, frequently
undergoing the microbial contamination (average contamination
by microorganisms and/or their spores can reach up
10 5 –10 8 microorganisms per gram) 1 . Thus γ-irradiation treatment
is accepted as one of the most effective sterilization
technique.
Toxicological and nutritional tests proved the safety
of γ-radiation doses below 10 kGy, which was accepted by
Codex Alimentarius (CA) General Standard for irradiated
foods as the maximum legal/allowed absorbed dose for dried
aromatic herbs, spices and vegetable seasonings sterilisation,
with the exception for cases when the higher dose application
is necessary to achieve a legitimate technological purpose 2 .
In contradiction to CA standards, the limitation of US Food
and Drug Administration (FDA) set the maximum allowed
dose for culinary herbs and spices to 30 kGy 3 .
Besides the positive effects of γ-radiation, its negative
impact on environment or even on human health forces the
food control authorities to develop reliable and sensitive
methods applicable for dosimetric purposes even long time
after the radiation process.
It is well known, that γ-radiation of food samples results
in the formation of free radical species. Thus, Electron Paramagnetic
Resonance (EPR) spectroscopy represents a suitable
tool to investigate the irradiated spice. 5–12 As follows
from several recently published data, the application of EPR
spectroscopy for dosimetric purposes is limited by several
factors, mostly by limited lifetime and thermal stability of
γ-radiation induced radicals. 5–13
Our previous investigations were focused on the monitoring
of radiation-induced changes e.g., in black pepper, oregano,
allspice, ginger, or clove. 5,9–12
The aim of the present study was to monitor the effect
of γ-irradiation on the microbiological quality of powder
samples of ground dry caraway seed (Carum carvi, L.) and
ground dry laurel leaves (Laurus nobilis, L.). The influence
of absorbed dose on the character of formed paramagnetic
structures, as well as their life-time was investigated by means
of EPR spectroscopy. Moreover, antioxidant properties of
individual spice extracts were characterized using both EPR
and UV-VIS spectrophotometer by means of 1,1-diphenyl-
2-picrylhydrazyl ( • DPPH), 2,2’-azinobis (3-ethylbenzothiazoline-6-sulfonic
acid) diammonium salt (ABTS +• ) radicals,
ferric reducing power (FRP) and thiobarbituric acid reactive
substances (TBARS) assays. Total contents of polyphenols
s560
(TPC) in each extract was also monitored and expressed as
Gallic acid equivalent. In addition, multivariate statistical
methods were used for the discrimination of native (non-irradiated)
samples from that exposed to γ-radiation.
Experimental
S a m p l e s C h a r a c t e r i s a t i o n
Samples of ground dry caraway seed (dry matter content,
92.1 %) originating from Austria and laurel leaves (dry
matter content, 92.5 %) from Turkey were provided by Kotanyi,
GmbH, Vienna, Austria. Spice samples were irradiated
using 60 Co source at average doses of 5, 10, 20 and 30 kGy
(dose rate, 2 kGy h –1 ) according to commercial practices at
Artim, Ltd. (Prague, Czech Republic). After the irradiation,
all the samples were stored in closed bags in the darkness at
ambient conditions.
M i c r o b i o l o g i c a l A n a l y s i s
Elementary microbiological analysis of all spice samples
(total counts of microorganisms, presence of coliform bacteria,
yeasts and moulds) was carried out following the relevant
STn ISO standards two times: immediately after the irradiation
and after 6 months of post-irradiation storage. 14–16
E P R E x p e r i m e n t s
EPR experiments with solid samples were performed
identically as previously described elsewhere, using a portable
X-band EPR spectrometer e-scan (Bruker, GmbH, Karlsruhe,
Germany). 5,10–12 Spice sample (100 mg) was placed in
the thin-wall EPR quartz tube (internal diameter, 3 mm) and
cylindrically shaped column was formed (sample column
heights: 2.1 ± 0.2 cm (caraway) and 2.0 ± 0.2 cm (laurel
tree), respectively; and then inserted into the standard rectangular
cavity of EPR spectrometer.
Ethanolic extracts of spice samples were prepared identically
as described in our previously published papers, by
mixing 0.4 g of respective spice sample with 8 ml ethanol of
spectroscopic grade. 5,10,12 Their ability to terminate • DPPH
and ABTS •+ radicals was monitored. 5,10,12,17,18
Experimental EPR spectra were recorded at 298 K. The
response and settings of EPR spectrometers were checked by
means of solid DPPH and Strong pitch standards (Bruker)
daily before the experiments, The obtained spectra were evaluated
using WIn EPR and SimFonia software (Bruker) as
described e.g. in. 5,9–11,19,20
U V - V I S E x p e r i m e n t s
Extracts used in UV-VIS experiments were prepared by
mixing 2.0 g of respective spice sample with 50 ml methanol/
water (80 %, v/v) solvent 9,11 . Double-beam UV-VIS spectrometer
Specord M40 (Carl Zeiss, Jena, Germany) with accessories
was used for the monitoring of antioxidant properties.
All the experiments were carried out in the same square quartz
UV-VIS transparent cells (path length, 1 cm). The monitoring
of antioxidant ability of spices’ extracts was performed