Abstract
The market availability of irradiated products requires proper labeling to safeguard the consumer’s right of choice. Ten commercial cinnamon powders of different origins were investigated to confirm their irradiation history using photostimulated-luminescence, thermoluminescence, and electron spin resonance analyses. Photostimulated-luminescence analysis screened out one sample as an intermediate (700–5000 PCs) while all others were negative. Upon thermoluminescence analysis, two samples yielded weak but clear peaks in the temperature range of 150–250oC, showing the possibility of irradiation. The electron spin resonance analysis showed limited sensitivity for all the commercial samples with the absence of radiation-specific features. The applicability of these techniques was confirmed by analyzing the radiation-induced detection markers in the in-house irradiated samples. Hygienic quality parameters and physicochemical properties (moisture content, pH, Hunter’s color, and particle size) showed variable results which can affect the quality of end product and should be taken into serious considerations to ensure hygienic quality and practical applications of cinnamon powders.
INTRODUCTION
Flavoring, preservative, and functional properties of different herbs and spices are well-known in different cultures.[Citation1] Among them, cinnamon bark obtained from Cinnamomum verum (Ceylon cinnamon) of the Lauraceae family is widely used in cookery as a condiment and flavoring material. This is also being used to cure different diseases[Citation2] where cinnamic aldehyde (cinnamaldehyde) is a main compound responsible for its valuable anti-allergenic, anti-inflammatory, anti-ulcerogenic, anti-pyretic, and anaesthetic activities.[Citation3Citation4] Considering the antioxidant,[Citation5−Citation7] anti-microbial,[Citation8Citation9] and anti-inflammatory effects[Citation10] of cinnamon, its possible role in the treatment of cancer, human melanoma, and Alzheimer’s disease was also suggested.[Citation11Citation12]
The initial microbial load in spices and herbs, in particular spore-forming bacteria, could be a serious threat for the hygienic safety of final-processed products. Even though spices are usually used in very minute quantities, once enough moisture is present, a significant increase in microbes could cause an unacceptable risk for the consumer safety.[Citation13] The situation requires an effective and advanced preservation method with negligible changes in the quality attributes of spices.
Food irradiation can enhance the hygienic quality of herbs and spices by reducing the pathogenicity and spoilage caused by microorganisms.[Citation14] Currently, irradiated spices are a major share of the irradiated foods in international trade; however, due to strict monitoring requirements, proper labeling is mandatory for the marketing of irradiated foods.[Citation15] The Reference Bureau of the Commission of the European Communities (Brussels) and the joint division of the FAO and IAEA had a significant role in the development of different detection methods for irradiated food. Consequently, different analytical techniques, such as photostimulated luminescence (PSL), thermoluminescence (TL), and electron spin resonance (ESR) analyses were devised to examine the irradiation status of irradiated foods, particularly herbs and spices. Principally, the luminescence techniques depend upon light emission from the inorganic-contaminating minerals through external light or heat stimulus.[Citation16−Citation18] On the other hand, ESR-based detection of radiation-specific cellulose or crystalline sugar radicals could be effectively used to characterize the irradiation history of different spices.[Citation16Citation19]
The aim of this work was to investigate the irradiation status of cinnamon powders, which are available in Korean market and to determine if they are in conformance with related regulations. Hence, the application potential of PSL, TL, and ESR techniques was determined. Various microbiological and physicochemical characteristics were also compared to complete a detailed quality overview of the samples.
MATERIALS AND METHODS
Samples and Irradiation
Ten cinnamon powder samples (without any labeling of irradiation), five imported from Vietnam and one each from China, America, India, Indonesia, and Belgium were collected from local markets. All samples were directly subjected to physicochemical, microbiological, and irradiation detection examinations (n = 3) as described in the following sections. In order to investigate the irradiation response of the detection markers and confirm the applicability of different detection techniques, the samples were irradiated (0, 1, and 5 kGy at dose rate of 2.1 kGy/h,) at room temperature using a Co-60 gamma-ray source (AECL, IR-79, Nordion International Co. Ltd., Ottawa, ON, Canada) at the Korean Atomic Energy Research Institute (KAERI), in Jeongeup, Korea. Dosimetry was performed using alanine dosimeters with a diameter of 5 mm (Bruker Instruments, Rheinstetten, Germany), and the free-radical signals were measured by a Bruker EMS 104 EPR analyzer (Bruker Instruments).
Irradiation Detection Analysis
PSL measurements were done using a PPSL system (serial; 0021, SURRC; Scottish Universities Research and Reactor Center, Glasgow, UK) composed of a control unit, sample chamber, and detector head assembly. The method EN 13751[Citation17] includes for sample preparations, measurement of photon counts (PCs), and interpretation of results. The samples were in a uniform thick layer within 50 mm diameter disposable Petri dishes (Bibby sterilin type 122), with no other preparation, and were measured in the sample chamber. The radiation-induced PCs (PPSL signal) emitting per second from the irradiated samples were automatically accumulated by a personal computer showing the PCs accumulated for up to 60 sec. The samples were measured in triplicate under the same laboratory and instrumental conditions. PCs less than 700 PCs/min were considered negative (non-irradiated) and more than 5000 PCs/min were considered as positive (irradiated). The value between these two limits was addressed as intermediate, which required further investigation.
TL analysis was conducted as described in the EN 1788[Citation18] standard method. The silicate minerals were separated from the samples (100 g) by density separation method. The separated minerals were deposited on clean stainless steel discs and kept overnight at 50oC in a dry oven. TL measurements were carried out using a TL reader (Harshaw 4500, Thermo Fisher Scientific Inc. Waltham, MA, USA) in the 50–400oC temperature range with a heating rate of 6oC/sec. A first read-out was performed on the extracted minerals to get the first glow curve, TL1. To normalize the TL response, the samples were re-irradiated at 1 kGy. The discs were again stored overnight at 50oC in a laboratory oven and then measured again, obtaining the second glow curve, TL2. Full-process blanks were made through all the steps of the procedures and were measured with the sample discs. Sample classification (irradiated or non-irradiated) was based on the TL1 shape and TL ratio (TL1/TL2) of the glow curve integral evaluated over the temperature range of 150–250oC. The sample was identified as irradiated when having a high intensity of TL glow curve with a peak before 250oC and a TL ratio greater than 0.1.
For the ESR analysis, approximately 0.1 g of ground sample was placed in a quartz ESR tube (5 mm diameter). The protocol EN 1787[Citation19] was used to measure the ESR signals, targeting the radiation-induced cellulose radicals using an X-band ESR spectrometer (JES-TE 300, Jeol Co., Tokyo, Japan) at room temperature under the following conditions: Microwave power, 5 mW; microwave frequency, 9.10–9.11 GHz; center field, 324 ± 2 mT; sweep width, 10–25 mT; modulation frequency, 100 kHz; modulation width, 1–2 mT; amplitude, 50–400; sweep time, 30 s; and time constant, 0.03 s.
Microbiological Analysis
All samples were analyzed for their total aerobic bacteria, yeasts and molds, and coliform counts. Five grams of cinnamon powder were mixed with 45 mL of sterile peptone water. Subsequent dilutions were prepared and plated on different media (Difco Lab., Sparks, MD, USA), such as plate count agar for the total aerobic bacteria, potato dextrose agar (acidified with 10% tartaric acid) for yeasts and molds, and desoxycholate agar for coliforms. Microbial counting was performed 24–48 h after incubation at 30 and 37°C for total aerobic bacteria and coliforms, respectively. Yeast and mold colonies were counted three days after incubation at 30°C.
Physicochemical Analysis
The moisture content was determined using an infrared moisture determination balance (FD-240, Kett Electric Laboratory, Tokyo, Japan). Approximately 1 g of each sample was used to determine the moisture percentage. The pH was determined using a pH meter (Thermo Scientific Orion Star Series, USA). The sample extracts were prepared by mixing 2 g of powder samples with 80 mL of distilled water in a shaker-incubator for 3 h at 200 rpm. The mixture was centrifuged, and the supernatant was filtered (Whatman #41).
For color determinations, the samples were placed into a Petri dish (diameter 4.5 mm) and measured (nine replicates) by a MINOLTA CR-200 colorimeter (Minolta Camera Co., Osaka, Japan). The color values were expressed as L (lightness/darkness), a (redness/greenness), b (yellowness/blueness) and total color difference ΔE (√ΔL2+Δa2+Δb2).
The particle size distribution of cinnamon powders was estimated by laser diffraction (N5/LS-13320, Beckman Coulter, Brea, CA, USA). Air was used as the dispersion agent for the particles from the inlet to the sample cell. Approximately 15 g of cinnamon powder were loaded into the feeding tray. The dispersion air pressure was adjusted to 1.0 bar. Three percent obscuration was achieved throughout the duration of the measurement.
Statistical Analysis
Measurements were performed at least three times (n = 3), and mean values (± standard deviation) were reported. The results were analyzed using Microsoft excel (Microsoft Office 2007 version) and Origin 8 software.
RESULTS AND DISCUSSION
PSL Characteristics
The contaminating inorganic dust, particularly silicate minerals, can be found in food materials. Upon irradiation, these minerals can store energy in charge carriers trapped at structural, interstitial or impurity sites. The optical stimulation of these minerals releases these charge carriers in the form of measurable luminescence that provides information about the irradiation status of the samples.[Citation17Citation18] The PSL methodology for the detection of irradiated food consists of screening (initial) PSL measurements to establish the status of the samples. A second measurement could be conducted following a calibration radiation-dose to determine the PSL sensitivity of the samples.[Citation17] illustrates the results of the PSL PCs for the non-irradiated commercial and gamma-irradiated samples. The PCs of all the commercial samples had negative results (< 700 PCs) with the exception of one sample that had an intermediate result (700–5000 PCs). All the samples, irradiated with a known dose of 1 kGy to check the PSL response of the samples, were positive (> 5000 PCs) expect for one sample that had a negative result (< 700 PCs). The sensitivity of the PSL technique depends upon the quantity and quality of the inorganic minerals on the surface of the samples.[Citation17Citation20] Therefore, the PSL response was greatly variable among the studied samples where the PCs ranged from 675 to 281,741. The calibrated PSL results showed that the PSL analysis was effective in screening all samples except for one with a very low PSL response.[Citation17] The commercial sample with an intermediate result (1462 PCs) had a high count of 61,913 PCs after the calibration dose. This result shows that at least the whole sample was not irradiated and that the sample had contaminating minerals enough to yield clear PSL results.[Citation17] The PSL method is a time-efficient method that can only be applied to screening a large number of samples according to their irradiation history; however, confirmatory techniques, such as TL and ESR analysis, are required to get reliable results.[Citation21]
Table 1 Photostimulated luminescence properties of various cinnamon powders available in Korean market
TL Characteristics
TL analysis is considered a most promising method for the detection of irradiated food materials from which silicate minerals (contaminating dust) could be isolated. Feldspar and quartz are well-known silicate minerals for their radiation-specific TL characteristics.[Citation18] In this study, the TL analysis was conducted as a confirmatory technique after density separation of the silicate minerals.[Citation18] Eight commercial samples showed a TL glow curve of low intensity without any characteristic peak in the TL temperature range of 150–250oC () giving a clear indication of the absence of an irradiation history. However, two samples had weak but clear TL peaks in the temperature range (150–250oC) specific for radiation treatment. The results were further confirmed by calculating the TL ratio (TL1/TL2) after re-irradiation of the TL minerals that were already measured. All samples had a TL ratio <0.1 (). The positive glow curve results from the two samples (CP-2 and 10) that were not confirmed by TL ratio might be because of the inclusion of irradiated material at very low quantities.[Citation22] In this case, monitoring of the samples should be continued and further scrutiny is necessary. Ahn et al.[Citation23] reported similar results showing the effect of irradiated components in a low quantity on the overall features of the TL glow curve, in which the results were not confirmed by TL ratio (). Thermally-processed irradiated samples could also result in similar TL characteristics, in which the glow curve and intensity yield useful information for detection purposes.[Citation24] The use of the TL glow curve shape and intensity only for the identification of irradiation was also reported by other researchers.[Citation25] To check the TL response of the samples, all samples were irradiated with 5 kGy of irradiation. The irradiated samples had characteristic TL glow curves with maximum peaks in the range of 150–250oC and the results were confirmed by a TL ratio > 0.1. Irradiation-specific TL response was also reported by other scientists to accurately evaluate the irradiation history of food samples.[Citation20Citation26Citation27]
Figure 1 TL glow curves of various cinnamon powders available in the Korean market.
Figure 2 TL ratio (TL1/TL2) of various cinnamon powders available in the Korean market.
ESR Properties
The unpaired electrons due to the defects in semiconductors, paramagnetic ions derived from transition or main group elements and free radicals can be examined by ESR spectroscopy. The ESR-based detection of radiation-specific radicals in food samples results in an effective and non-destructive technique to analyze the irradiation status of samples.[Citation19] An ESR investigation on the freeze-dried commercial samples was conducted to identify the radiation-induced signals. A single central ESR signal (g-value 2.005) was determined in all samples irrespective of their irradiation history (). This natural signal might be due to the semiquinone radicals, which are induced by the oxidation of polyphenols in the plant food matrix.[Citation28Citation29] However, all commercial cinnamon samples were silent for radiation-induced signals, whereas the effect of Mn2+ on either side of the main signal was also evident in some samples.[Citation27] Upon irradiation, all the samples had the typical cellulose radical spectra of the main central signal (g-value 2.0061) with two side peaks (). The central signal (g = 2.005) that was also clear in all the commercial samples showed a significant increase following irradiation treatment. The radiation-induced side peaks were found at approximately ±3 mT (g = 2.0253 and 1.9883) to either side of the main ESR signal which were also reported in different irradiated food materials of plant origin.[Citation30Citation31] Different scientists have reported the variable intensities of these two radiation-specific side peaks with respect to the main ESR signal, mainly depending upon the kind of sample and its pretreatments.[Citation32Citation33] The results showed that the luminescence techniques, particularly TL analysis, were more sensitive than the ESR analysis to determine the irradiation status of the unknown cinnamon samples. The practicality of TL analysis over other available methods to detect irradiated fresh mushrooms,[Citation27] composite seasoning foods,[Citation34] wheat, and corn[Citation35] was also reported previously.
Table 2 Microbiological quality of various cinnamon powders available in Korean market
Figure 3 ESR spectra of various cinnamon powders available in the Korean market.
Microbiological Quality
The microbiological quality of herbs and spices mainly depends upon hygienic practices adopted during their cultivation and especially during post-harvest processing.[Citation36] The initial microbial load on herb and spices may be very high with a diverse indigenous microflora as these are cultivated, harvested, and processed in warm and humid climatic conditions. Herbs and spices usually have significant stability with the least changes in their microbial load during proper storage mainly due to their low moisture content and natural antimicrobial agents.[Citation1Citation37] However, microbial contamination could have drastic results with poor hygienic quality upon mixing these spices with foods having high moisture content.[Citation13] The microbial hazard could be more serious if the spices and herbs containing pathogenic microorganisms are added into meals that do not need any prior treatment before final consumption.[Citation38] Scientists have reported on the poor hygienic quality of black pepper, paprika, chili powder, and cumin seeds with microbial counts up to 108 CFU/g.[Citation39Citation40] However, spices are generally added in low quantities, which limit the potential microbial hazard associated with them. Therefore, complete sterilization of herbs and spices is usually not recommended, but the microbial count should be preferably below 103–104 CFU/g.[Citation13] In this study, the commercial cinnamon powder samples had an aerobic bacterial count in the range of 102 to 105 CFU/g with a minimum value of 5 × 102 CFU/g (CP-10); the same sample was negative for yeast and molds count while others were in the range of 103 to 104 CFU/g (). All the samples were negative for coliform count. Among other treatments, irradiation is effective to improve hygienic quality; however commercial samples did not show valid evidence of irradiation treatment. In this study, all the commercial samples were of acceptable microbiological quality as recommended by the European Spice Association (ESA) and can be regarded as microbiologically safe if stored and distributed under proper conditions. However, it is not possible to select a single microbial quality index as these are being used in different forms, quantities, and kinds of final products. The quality of the end product should be taken into consideration before deciding the desired microbiological quality index.[Citation38Citation41]
Table 3 Physicochemical qualities (moisture contents, pH and Hunter’s color value) of various cinnamon powders available in Korean market
Table 4 Particle size and cumulative size distribution of various cinnamon powders available in Korean market
Physicochemical Properties
Generally, spices are used in very small quantities in different food preparations as “food additive” and contribute little to human nutrition. However, various key quality attributes of dried spices are important for their delicate but essential role in the acceptance of different processed foods.[Citation42] The physicochemical properties of commercial cinnamon powder samples are presented in . pH was recorded in the range of 4.93 to 5.07 with an average value of 5.02, while the moisture content ranged from 7.25 to 12.73% with an average value of 10.04%. The low pH represented an increased amount of organic acids in the samples. Cinnamaldehyde, followed by cinnamyl acetate are the organic compounds that affect its pH and give cinnamon its characteristic flavor and odor.[Citation43,Citation44] Low pH and moisture content could ensure improved hygienic quality of spices during their storage. Hunter’s color L, a, and b values were in the ranges of 40.47–51.53, 12.33–25.25, and 9.16–18.19, respectively. Reduced L and b values indicated darker color, whereas the degree of redness was represented with a higher a value. Principal component analysis was conducted that showed different patterns () depending upon the samples. It demonstrated the clear variation in quality profiles of different samples. The average particle sizes of all the samples were comparable having a maximum value of 294 μm except for one low value of 58 μm (, ). Color and particle size parameters are important for consumer acceptability and different industrial applications of spices. The large differences in quality attributes, which may depend on origin of production, differences in processing, packaging, and storage of these cinnamon powder samples suggest a need for a criterion that is specific for a single powder spice, especially cinnamon powders rather than criteria for all the spices.
Figure 4 Principal component analysis of physicochemical qualities (moisture, pH, and Hunter E) of various cinnamon powders available in the Korean market.
Figure 5 Particle size of various cinnamon powders available in the Korean market.
CONCLUSIONS
For the unknown commercial samples, an intermediate PSL count was found for one sample showing probability of irradiation treatment. TL analysis yielded the most effective characterization of the irradiation history of the samples in which a weak but clear peak in the temperature range of 150–250oC was found in two commercial samples including one that was intermediate upon PSL analysis. However, the TL ratios (TL1/TL2) of all the commercial samples were < 0.1. The ESR results showed no radiation-specific signals for all the commercial samples. PSL, TL, and ESR techniques were found effective to detect radiation-induced markers in the irradiated cinnamon samples. There was a great variation in different microbial and physico-chemical quality attributes among the samples and a quality standard specific to cinnamon powder was required, which could be important for the development of uniform quality products using cinnamon powder as an ingredient.
FUNDING
This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) grant funded by the Ministry of Education (MOE) (No. NRF- 2013R1A1A4A03006993).
REFERENCES
- Gupta, M. Pharmacological properties and traditional therapeutic uses of important Indian spices: A review. International Journal of Food Properties 2010, 13, 1092–1116.
- Qin, B.; Panickar, K.S.; Anderson, R.A. Cinnamon: Potential role in the prevention of insulin resistance, metabolic syndrome, and type 2 diabetes. Journal of Diabetes Science and Technology 2010, 4, 685–693.
- Kurokawa, M.; Kumeda, C.A.; Yamamura, J.; Kamiyama, T.; Shiraki, K. Antipyretic activity of cinnamyl derivatives and related compounds in influenza virus-infected mice. European Journal of Pharmacology 1998, 348, 45–51.
- Qin, B.; Dawson, H.; Polansky, M.M.; Anderson, R.A. Cinnamon extract attenuates TNF-alpha-induced intestinal lipoprotein ApoB48 overproduction by regulating inflammatory, insulin, and lipoprotein pathways in enterocytes. Hormone and Metabolic Research 2009, 41, 516–522.
- Lin, C.C.; Wu, S.J.; Chang, C.H.; Ng, L.T. Antioxidant activity of Cinnamomum cassia. Phytotherapy Research 2003, 17, 726–730.
- Okawa, M.; Kinjo, J.; Nohara, T.; Ono, M. DPPH (1,1-diphenyl-2- picrylhydrazyl) radical scavenging activity of flavonoids obtained from some medicinal plants. Biological and Pharmaceutical Bulletin 2001, 24, 1202–1205.
- Toda, S. Inhibitory effects of aromatic herbs on lipid peroxidation and protein oxidative modification by copper. Phytotherapy Research 2003, 17, 546–548.
- Inouye, S.; Takizawa, T.; Yamaguchi, H. Antibacterial activity of essential oils and their major constituents against respiratory tract pathogens by gaseous contact. Journal of Antimicrobial Chemotherapy 2001, 47, 565–573.
- Smith-Palmer, A.; Stewart, J.; Fyfe, L. Antimicrobial properties of plant essential oils and essences against five important food-borne pathogens. Letters in Applied Microbiology 1998, 26, 118–122.
- Tung, Y.T.; Chua, M.T.; Wang, S.Y.; Chang, S.T. Anti-inflammation activities of essential oil and its constituents from indigenous cinnamon (Cinnamomum osmophloeum) twigs. Bioresource Technology 2008, 99, 3908–3939.
- Ka, H.; Park, H.J.; Jung, H.J.; Choi, J.W.; Cho, K.S.; Ha, J. Cinnamaldehyde induces apoptosis by ROS-mediated mitochondrial permeability transition in human promyelocytic leukemia HL-60 cells. Cancer Letters 2003, 196, 143–152.
- Peterson, D.W.; George, R.C.; Scaramozzino, F.; LaPointe, N.E.; Anderson, R.A.; Graves, D.J.; Lew, J. Cinnamon extract inhibits tau aggregation associated with Alzheimer’s disease in vitro. Journal of Alzheimer’s Disease 2009, 17, 585–597.
- Witkowska, A.M.; Hickey, D.K.; Alonso-Gomez, M.; Wilkinson, M.G. The microbiological quality of commercial herb and spice preparations used in the formulation of a chicken supreme ready meal and microbial survival following a simulated industrial heating process. Food Control 2011, 22, 616–625.
- Khan, A.K.; Abrahem, M. Effect of irradiation on quality of spices. International Food Research Journal 2010, 17, 825–836.
- Kume, T.; Furuta, M.; Todoriki, S.; Uenoyama, N.; Kobayashi, Y. Status of food irradiation in the world. Radiation Physics and Chemistry 2009, 78, 222–226.
- Arvanitoyannis, I.S. Irradiation detection. In: Irradiation of Food Commodities: Techniques, Applications, Legislation, Safety and Consumer Opinion; Academic Press Publications: London, 2010; 67–139.
- EN 13751. Foodstuffs–detection of irradiated food using photostimulated luminescence. European Committee of Standardization (CEN), Brussels, Belgium, 2009.
- EN 1788. Foodstuffs–detection of irradiated food from which silicate minerals can be Isolated: Method by thermoluminescence. European Committee of Standardization (CEN), Brussels, Belgium, 2001.
- EN 1787. Foodstuffs–detection of irradiated food containing cellulose by ESR spectroscopy. European Committee of Standardization (CEN), Brussels, Belgium, 2000.
- Bayram, G.; Delincée, H. Identification of irradiated Turkish foodstuffs combining various physical detection methods. Food Control 2004, 15, 81–91.
- Chauhan, S.K.; Kumar, R.; Nadanasabapathy, S.; Bawa, A.S. Detection methods for irradiated foods. Comprehensive Reviews in Food Science and Food Safety 2009, 8, 4–16.
- Kim, B.; Akram, K.; Kim, C.T.; Kang, N.R.; Lee, J.W.; Ryang, J.H.; Kwon, J.H. Identification of low amount of irradiated spices (red pepper, garlic, ginger powder) with luminescence analysis. Radiation Physics and Chemistry 2012, 81, 1220–1223.
- Ahn, J.J.; Akram, K.; Lee, J.; Kim, K.S.; Kwon, J.H. Identification of a gamma-irradiated ingredient (garlic powder) in Korean barbeque sauce by thermoluminescence analysis. Journal of Food Science 2012, 77, 476–480.
- Lee, J.; Kausar, T.; Kim, B.; Kwon, J.H. Detection of γ-irradiated sesame seeds before and after roasting by analyzing photostimulated luminescence, thermoluninescence, and electron spin resonance. Journal of Agricultural and Food Chemistry 2008, 56, 7184–7188.
- Sanderson, D.C.W.; Carmichael, L.A.; Fisk, S. Establishing luminescence methods to detect irradiated foods. Food Science and Technology Today 1998, 12, 97–102.
- Jo, D.; Kim, B.K.; Kausar, T.; Kwon, J.H. Study of photostimulated- and thermo-luminescence characteristics for detecting irradiated kiwifruit. Journal of Agricultural and Food Chemistry 2008, 56, 1180–1183.
- Akram, K.; Ahn, J.J.; Kim, G.R.; Kwon, J.H. Applicability of different analytical methods for the identification of γ-irradiated fresh mushrooms during storage. Food Science and Biotechnology 2012, 21, 573–579.
- Dismukes, G.C.; McGuire, A.; Blankenship, R.; Sauer, K. Electron spin polarization in photosynthesis and the mechanism of electron transfer in photosystem I. Experimental observations. Biophysics Journal 1978, 21, 239–256.
- Calucci, L.; Pinzino, C.; Zandomeneghi, M.; Capocchi, A.; Ghiringhelli, S.; Saviozzi, F.; Tozzi, S.; Galleschi, L. Effects of γ-irradiation on the free radical and antioxidant contents in nine aromatic herbs and spices. Journal of Agricultural and Food Chemistry 2003, 51, 927–934.
- Raffi, J.J.; Agnel, J.P.L. Electron spin resonance identification of irradiated fruits. Radiation Physics and Chemistry 1989, 34, 891–894.
- de Jesus, E.F.O.; Rossi, A.M.; Lopes, R.T. Identification and dose determination using ESR measurements in the flesh of irradiated vegetal products. Applied Radiation and Isotopes 2000, 52, 1375–1383.
- Yamaoki, R.; Tsujino, T.; Kimura, S.; Mino, Y.; Ohta, M. Detection of organic free radicals in irradiated Foeniculi fructus by electron spin resonance spectroscopy. Journal of Natural Medicines 2009, 63, 28–31.
- Tabner, B.J.; Tabner, V.A. An electron spin resonance study of gamma-irradiated citrus fruits. Radiation Physics and Chemistry 1993, 41, 545–552.
- Kwon, J.H.; Kim, M.Y.; Kim, B.K.; Chung, H.W.; Kim, T.C.; Kim, S.J. The detection of irradiated composite seasoning foods by analyzing photostimulated luminescence (PSL), electron spin resonance (ESR) and thermoluminescence. Korean Journal of Food Preservation 2006, 13, 55–60.
- Kim, G.R.; Lee, J.W.; Kim, J.S.; Kwon, J.H. Physical detection properties of irradiated wheat and corn treated with different radiation sources. Korean Journal of Food Preservation 2009, 16, 211–216.
- Rajeev, B. Potential use of Fourier transform infrared spectroscopy for identification of molds capable of producing mycotoxins. International Journal of Food Properties 2013, DOI:10.1080/10942912.2011.609629
- Koffi-Nevry, R.; Kouassi, K.C.; Nanga, Z.Y.; Koussemon, M.; Loukou, G.Y. Antibacterial activity of two bell pepper extracts: Capsicum annum L. and Capsicum frutescens. International Journal of Food Properties 2012, 15, 961–971.
- Banerjee, M.; Sarkar, P.K. Microbiological quality of some retail spices in India. Food Research International 2003, 36, 469–474.
- Bhat, R.; Geeta, H.; Kulkarni, P.R. Microbial profile of cumin seeds and chili powder sold in retail shops in the city of Bombay. Journal of Food Protection 1987, 50, 418–419.
- McKee, L.H. Microbial contamination of spices and herbs: A review. LWT-Food Science and Technology 1995, 28, 1–11.
- Schwab, A.H.; Harpestad, A.D.; Swartzentruber, A.; Lanier, J.M.; Wentz, B.A.; Duran, A.P.; Barnard, R.J.; Read, R.B. Microbiological quality of some spices and herbs in retail markets. Applied and Environmental Microbiology 1982, 44, 627–630.
- Pruthi, J.S. Chemistry and quality control of Capsicums and Capsicum products. In: Capsicum: The genus Capsicum; De, A.K.; Eds.; CRC Press: London, 2003; 25–70.
- Leela, N.K. Cinnamon and cassia. In: Chemistry of Spices; Parthasarathy, V.A.; Bhageerathy, C.; Zachariah, T.J.; Eds.; CAB International: Wallingford, Oxfordshire, 2007; 124–145.
- Woehrlin, F.; Fry, H.; Abraham, K.; Preiss-Weigert, A. Quantification of flavoring constituents in cinnamon: High variation of coumarin in cassia bark from the German retail market and in authentic samples from Indonesia. Journal of Agricultural and Food Chemistry 2010, 58, 10568–10575.