IDENTIFICATION OF IRRADIATED SPAGHETTI SAUCES USINGDIFFERENT PHYSICAL TECHNIQUESKASHIF AKRAM1, JAE-JUN AHN1, GUI-RAN KIM1 and JOONG-HO KWON1,2

1Department of Food Science & Technology, Kyungpook National University, Daegu 702-701, Republic of Korea

2Corresponding author. TEL:+82-53-950-5775; FAX: +82-53-950-6772;EMAIL: jhkwon@knu.ac.kr

Received for Publication November 18, 2011Accepted for Publication May 15, 2012

10.1111/j.1745-4557.2012.00450.x

ABSTRACT

Gamma-irradiated (0, 1, 5 and 10 kGy) spaghetti sauce samples were identified usingphotostimulated luminescence (PSL), thermoluminescence (TL) and electron spinresonance (ESR) techniques. PSL technique was used as a screening method for irra-diated sauce samples, where the improved results of PSL method were observed forthe freeze-dried and alcoholic-extracted samples. TL technique, through the densityseparation step of silicate minerals from irradiated samples, gave specific shape,intensity and occurrence of TL glow curve in a typical temperature range as well asTL ratio (TL1/TL2) to identify the irradiation treatment. The ESR method employedfor the freeze-dried samples, showed radiation-specific cellulose signals for 5 and10 kGy-treated samples, and the results were comparable with oven-dried samples.In general, TL technique was found the most sensitive and reliable for the identifica-tion of irradiated spaghetti sauces.

PRACTICAL APPLICATIONS

The safety of food irradiation is well documented; however, this technique lacksinternational consensus for general applicability. Validated identification methodshave prime importance for the application of different regulations regarding theinternational trade of irradiated food. This study comprehensively investigated thepotential of different available techniques for the identification of irradiated saucesamples. Liquid samples were treated with different modified methods to find theimproved identification results. The presented results may be useful for differentregulatory authorities to identify or monitor irradiated spaghetti sauces.

INTRODUCTION

Different kinds of sauces are being used around the globe toenhance the taste of various food products (Martínez-Padillaand Rivera-Vargas 2006; Rengsutthi and Charoenrein 2011).Sauces are the liquid products containing different spicesand having desired flow ability and consistency to improveappearance, flavor, and texture of the food (Martínez-Padillaand Rivera-Vargas 2006). With their various and extensiveuse, the hygienic safety has a key importance for processersand health authorities. Various studies demonstrated theeffectiveness of irradiation to address the problem in differ-ent sauces associated with microbial contamination (Leeet al. 2001; Song et al. 2001; Jo et al. 2003). The major inter-national health organizations have accepted the potential ofthis technology to ensure the hygienic quality of food with

minimum nutritional losses (Farkas and Mohácsi-Farkas2011).

Despite the safety assurance of food irradiation at any doselevel by leading health authorities (WHO 1999), there are dif-ferent national and international regulations regarding fooditem categories and applied doses. The labeling of irradiatedfood is also mandatory to safeguard the consumer’s right ofchoice (Arvanitoyannis 2010). In this case, the commercializa-tion of this technology needs effective and reliable identifica-tion methods in compliance with the regulations.Luminescence techniques, such as photostimulated lumines-cence (PSL) and thermoluminescence (TL), and electron spinresonance (ESR) are being used extensively as physical detec-tion methods to serve the purpose (Chauhan et al. 2009).

All available methods have some limitations in termsof their specific application range, product to product

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Journal of Food Quality ISSN 1745-4557

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variation, complex food matrix and low concentration ofradiation-induced markers (Delincée 1998). Luminescencetechniques (PSL and TL) mainly depend upon the mineralpart of the product that is usually not inherent to food itselfand varies greatly with respect to food type and its origin. PSLis an easy technique and requires no sample pretreatmentgenerally but can only be used as a screening test and needs TLor ESR analysis to confirm the results (EN 1788 2001; EN13751 2009). ESR technique can be applied to solid foodscontaining cellulose, sugar and bone. For food items withhigh moisture, effective drying methods are required withleast/no effect on ESR spectrum, which is sensitive to adversetemperature conditions (Kikuchi et al. 2011). In this regard,extensive research on different food products is needed toascertain the effectiveness and reliability of the method.

The objective of the present study was to check the effec-tiveness and reliability of luminescence (PSL and TL) andESR techniques in detecting irradiated spaghetti sauce. Dif-ferent sample pretreatments were also tried for PSL and ESRanalyses to improve their results. The scope of EN protocolswas also extended by investigating their potential applicationsto irradiated liquid food products.

MATERIALS AND METHODS

Samples and Irradiation

Spaghetti sauce (Ottogi Co., Ltd. Anyang, Gyeonggi, SouthKorea) was purchased from a local market in Daegu, Koreaand stored at 5C. The samples were irradiated (0, 1, 5 and10 kGy) using a Co-60 gamma-ray source (AECL, IR-79,MDS Nordion International Co. Ltd., Ottawa, Canada) at theKorean Atomic Energy Research Institute (KAERI) inJeongeup, Korea. Dosimetry was performed to confirm therequired absorbed dose using alanine dosimeters of 5 mmdiameter (Bruker Instruments, Rheinstetten, Germany), andBruker EMS 104 EPR analyzer (Bruker Instruments) was usedto measure the free-radical signals.

PSL Analysis

PSL measurements were employed using a PPSL system(serial; 0021, SURRC; Scottish Universities Research andReactor Center, Glasgow, U.K.). Three different types ofsamples were used for PSL measurement:

i. Liquid sample without any treatmentii. Solid sample after freeze drying (Bondiro, Ilsin Bio Base,

Yangju, Kyunggi-do, Korea)iii. Solid sample after alcoholic extraction of moisture asdescribed by De Jesus et al. (1999).

The sample (about 2 g) was deposited as a uniform thick layerin disposable Petri dish (50 mm diameter; Bibby sterilin type

122) and was measured in the sample chamber. Theradiation-induced photon counts (PPSL signal) emitting persecond from the irradiated samples were automatically accu-mulated by a personal computer up to 60s. The method, EN13751 (2009), was used for measurement of photon counts(PCs) and interpretation of results. The PCs less than 700/60swere considered as negative (nonirradiated) and more than5,000/60s were considered as positive (irradiated). The valuebetween these two limits was reported as intermediate. Thesamples were measured in triplicate (n = 3) under the samelaboratory and instrumental conditions and mean values(�SD) were reported.

TL Analysis

The silicate minerals for TL analysis were separated from thesamples (100 g) by density separation method, and TL discswere prepared as described in the EN 1788 protocol (2001).The separated minerals were deposited on clean stainless steeldiscs and kept overnight at 50C in a laboratory oven. TL mea-surements were performed using a TL reader (Harshaw 4500,Thermo Fisher Scientific Inc.Waltham, MA) at 50–400C tem-perature range with a heating ramp of 6C/s. A first measure-ment was carried out on the extracted minerals to get the firstglow curve, TL1. To normalize the TL response, the sampleswere reirradiated at 1 kGy using the same source. The discswere again stored overnight at 50C and measured to get thesecond glow curve, TL2. Full-process blanks were prepared tocalculate minimum detectable level (MDL), and the sampleswith a TL2 glow curve intensity 10 times more than the MDLwere selected for the TL ratio calculation. TL1 shape, intensityand TL ratio (TL1/TL2) of the glow curve integral evaluatedover the temperature range of 150–250C were used for theinterpretation of results in accordance with EN 1788 (2001).

ESR Analysis

In ESR analysis of irradiated food, the food material with highmoisture content must be dried before measurement. In thisregard, freeze drying (Yordanov et al. 2006) and oven drying(Jo and Kwon 2006) methods were employed as pretreat-ments of the liquid sauce samples.

Approximately 0.1 g of the dried sample was placed in aquartz ESR tube (5 mm dia.). European standards EN 1787(2000) was applied to measure ESR signals targeting theradiation induced-cellulose signals. X-band ESR spectrom-eter (JES-TE 300, Jeol Co., Tokyo, Japan) was used at roomtemperature under the following conditions: power, 0.4–5 mW; frequency 9.18–9.21 GHz; center field, 327 � 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. Measurements were per-formed three times (n = 3), and mean values (�SD) were

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reported. The results were analyzed using Microsoft excel(Microsoft Office 2007 version) and Origin 8 software.

RESULTS AND DISCUSSION

PSL Properties

The PSL technique, using different sample pretreatments, wasemployed as a screening test; and the results are presented inTable 1. In case of PSL measurement of liquid samples, thenonirradiated control gave negative (<700 PCs), 1 and 5 kGygave intermediate (700–5,000 PCs), while 10 kGy irradiatedsample gave positive result (>5,000 PCs). A significantimprovement was obvious in solid samples, where freeze-dried samples showed the best PSL count. In freeze-driedsamples, the control was negative, while all irradiated sampleswere found to be positive. PSL is a rapid technique when usedas screening test, but freeze drying may take several days. Inthis case, the sample extracted with alcohol may be a goodchoice. Results from alcoholic-extracted samples were muchbetter than liquid samples and comparable with freeze-driedsamples, where all irradiated samples were positive except1 kGy-irradiated sample that gave an intermediated result.The silicate minerals present in the food samples are respon-sible for their luminescence characteristics. The dried samplesgot enriched with the mineral fraction providing relativebetter PSL count. Many scientists effectively used PSL as ascreening test for different food products, especially spices,dried fruits and dried vegetables (Sanderson et al. 2003;Bayram and Delincée 2004).

TL Characteristics

In identification of irradiated food, TL technique is consid-ered as the most promising confirmatory method to discrimi-nate irradiated from nonirradiated samples, which could beapplied to any food item with traces of silicate minerals (EN1788 2001). All irradiated samples showed TL glow curve ofhigh intensity in the temperature range of 150–250C (Fig. 1),whereas the TL glow curve of low intensity was found after300C, proving only geological signals in separated mineralsfrom nonirradiated samples. The nature (quartz, feldspar,carbonates, etc.) and the quantity of minerals on TL discs

have significant impact on TL signals (Soika and Delincée2000). Therefore, the European standard recommends thenormalization step to confirm the suitability of TL techniquesfor the minerals on the discs. TL2 was measured after reirra-diation (1 kGy) of the same TL discs having measured (TL1)samples to check suitability in terms of quality and quantityof separated minerals on the discs. TL ratios (Table 2) of allirradiated samples were more than 0.1, whereas nonirradi-ated samples showed TL ratios less than 0.1. This confirmedthe suitability of TL method for clear identification of studiedsamples. Our results were in good agreement with the TLresults reported for different food products especially spices,dried fruits and dried vegetables (Chauhan et al. 2009).

TABLE 1. PSL COUNTS OF GAMMA-IRRADIATED SPAGHETTI SAUCE AFTER DIFFERENT SAMPLE PRETREATMENTS

Sample state

Irradiation dose (kGy)

0 1 5 10

Liquid 260.3 � 57.1* (-)† 1,445.5 � 428.5 (M) 3,258.0 � 1,345.2 (M) 5,441.7 � 2,096 (+)Freeze dried 219.0 � 9.9 (-) 6,960.5 � 132.2 (+) 17,357.0 � 5,331.5 (+) 19,588 � 8,666.3 (+)Alcoholic extracted 515 � 42 (-) 2,955 � 165 (M) 7,945 � 196 (+) 17,992 � 5,139 (+)

* Mean � SD (n = 3).† Threshold value: T1 = 700 (nonirradiated), T2 = 5,000 (irradiated), (-) < T1, T1 < (M) < T2, (+) > T2.

50 100 150 200 250 300 350 400

0

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250

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in

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5 kGy

10 kGy

FIG. 1. TL GLOW CURVE OF MINERALS SEPARATED FROM GAMMA-IRRADIATED SPAGHETTI SAUCE

TABLE 2. TL INTENSITIES AND TL RATIOS (TL1/TL2) OF MINERALSSEPARATED FROM GAMMA-IRRADIATED SPAGHETTI SAUCE

Irradiation dose (kGy)

TL parameters

TL1 (nC) TL2 (nC) TL ratio

0 10.391 412.23 0.0251 128.31 826.1 0.1555 1,813.3 4,659.5 0.389

10 1,859.6 3,750.7 0.496

TL, thermoluminescence.

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ESR Properties

For ESR analysis, two types of sample pretreatments (freezedrying and oven drying) were employed. Nonirradiatedsamples in both cases showed a single central peak atg = 2.004, which originated from semiquinone radicals (Raffiet al. 2000; Calucci et al. 2003) and reported from differentplant materials (Raffi and Agnel 1989; Tabner and Tabner1991, 1993). The intensity of this signal was lower in the oven-dried sample than in the freeze-dried sample.

Upon irradiation, an increase in intensity of the centralsignal was found (Figs. 2 and 3) in both types of driedsamples. The overall signal intensity was lower in theoven-dried samples, which might be due to the use of hightemperature (Yordanov and Aleksieva 2009). Irradiation alsoinduced two side peaks (g = 2.0207 and g = 1.9854), whichwere clear in 5 and 10 kGy-irradiated samples. Theseradiation-induced side peaks were equally spaced at about�3 mT from the central signal and were ascribed toradiation-induced cellulose radicals (Raffi et al. 2000). These

side peaks were not clear in the 1 kGy-irradiated samplesof both treatments. Mn2+ signals were also found, makingthe ESR spectra difficult to analyze especially at low dose(1 kGy). A similar problem was also reported by Kikuchi et al.(2010) in ESR analysis of irradiated mango. The distancebetween radiation-induced two-side peaks (g1–g2 = 6.002 �

0.002 mT) and g values of side and central signals (g0 =2.0062 � 0.0002, g1 = 2.0245 � 0.0001 and g2 = 1.9863 �

0.0001) did not vary significantly with respect to differentdrying methods. De Jesus et al. (1999) also reported that dif-ferent sample pretreatments had negligible effect on g valuesand mutual distance of main and side peaks in fruit pulpsamples.

CONCLUSIONS

The PSL analysis using freeze-dried or alcoholic-extractedsamples proved better alternative to the liquid state of sample.The sample drying without use of high temperature couldenrich the silicate minerals in the sample, resulting in better

315 320 325 330 335

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FIG. 2. ESR SPECTRA OF FREEZE-DRIED GAMMA-IRRADIATED SPAGHETTI SAUCE

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PSL count. TL technique could provide a clear discriminationon the basis of TL glow curve shape, intensity, temperaturerange of TL peak maxima and TL ratio (TL1/TL2). The ESRmethod employed using the freeze-dried or oven-driedsamples showed radiation-specific cellulose signals in 5 and10 kGy-irradiated samples, where signal intensity was abouttwice in case of freeze-dried samples. Oven drying provided atime-efficient approach for the ESR analysis; however, the ESRtechnique was inappropriate to detect radiation-inducedmarkers in 1 kGy-irradiated sample. The studied physical tech-niques have potential to identify irradiation history of the spa-ghetti sauce.

ACKNOWLEDGMENT

This research was supported by the National Research Foun-dation (NRF) of Korea in 2012.

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