effect of pulsed light on safety and quality of fresh egg pasta

ORIGINAL PAPER

Effect of Pulsed Light on Safety and Quality of Fresh Egg Pasta

Lara Manzocco & Michela Maifreni & Monica Anese &

Marina Munari & Ingrid Bartolomeoli & Sandro Zanardi &Michele Suman & Maria Cristina Nicoli

Received: 20 May 2013 /Accepted: 7 October 2013# Springer Science+Business Media New York 2013

Abstract This study investigated the effect of pulsedlight (up to 26.25 J/cm2) on the inactivation ofSalmonella enterica and on the eventual occurrence ofundesirable changes in the quality of fresh egg pastajust after preparation and during storage at 4 °C. WhenS. enterica was inoculated on egg pasta surface, a lightdose of 0.70 J/cm2 sufficed to lower counts by 2.5 logunits while 3.50 J/cm2 were required for a 3.3 log unitreduction (below detection limit). For S. enterica inoc-ulated in the dough, a light dose of 3.50 J/cm2 loweredcounts by only 1.0 log unit while 17.50 J/cm2 wererequired for a 3.3 log unit reduction, due to the limitedlight penetration through egg pasta. At a dose of 1.75 J/cm2,pulsed light induced no significant changes in egg pastaappearance, oxidation state and sensory properties. Athigher doses, off-flavour formation was detected.Independently of the dose applied, pulsed light did notinduce furan formation and promoted an increase in theoxidative stability of egg pasta lipids as well as pigmentbleaching during storage. The latter was attributed to theformation of photo-induced non-enzymatic browningproducts.

Keywords Microbial decontamination . Oxidation .

Off-odour . Colour . Furan

Introduction

Pulsed light is nowadays recognised as an emerging non-thermal technology for the rapid inactivation of pathogenicand spoilage microorganisms in food (Oms-Oliu et al. 2010a;Gómez-López et al. 2007). It is based on the repetition ofconsecutive intense flashes of broad-spectrum light withwavelengths from the near-infrared region to the ultra-violet one (100–1,100 nm). Microbial inactivation ismainly attributed to photochemical damage caused bythe ultraviolet C (UV-C) component of pulsed light(Woodling and Moraru 2007; Krishnamurthy et al.2010). However, there is evidence that photothermaldamage can also occur (Takeshita et al. 2003).

Being scarcely penetrating, pulsed light is nowadays usedfor sterilisation of package surfaces. It has been also suggestedfor decontamination of the surface of solid foods, such as shelleggs, fresh-cut vegetables and ready-to-eat products (Hierroet al. 2011a, b; Ramos-Villarroel et al. 2011; Ozer and Demirci2006; Lasagabaster et al. 2011; Gómez et al. 2012).

The literature on pulsed light is rapidly expanding, but agap remains between research intended to identify optimaldecontamination conditions and their actual application. Amajor limitation to the extensive use of pulsed light lays inthe unknown boundary that discriminates technological con-ditions leading to antimicrobial effects from those impartingdisadvantageous quality depletion. In addition to microbialinactivation, food exposure to pulsed light is certainly associ-ated with photoreaction of food components, including lipids,antioxidants, flavour compounds and pigments. For instance,pulsed light is reasonably expected to induce the developmentof oxidative reactions and non-enzymatic browning in food.Moreover, exposure of sugar solutions to UV-C light wasfound to induce the formation of furan, which has beenclassified as “possibly carcinogenic to humans” by theInternational Agency on Cancer (IARC 1995). It must be

L. Manzocco (*) :M. Maifreni :M. Anese :M. Munari :I. Bartolomeoli :M. C. NicoliDipartimento di Scienze degli Alimenti, Università di Udine, viaSondrio 2/A, 33100 Udine, Italye-mail: lara.manzocco@uniud.it

S. Zanardi :M. SumanBarilla SpA, Food Science and Research Labs, Via Mantova 166,Parma, Italy

Food Bioprocess TechnolDOI 10.1007/s11947-013-1213-6

pointed out that scarce information is available on theeffect of pulsed light on the development of thesereactions in foods (Wu et al. 2008; Oms-Oliu et al.2010b; Manzocco et al. 2013).

Fresh egg pasta has been implicated in many Salmonellaenterica outbreaks (EFSA 2009). Its production generallyrequires a double pasteurisation heat treatment. The first oneis applied on the loose product while the second is carried outafter egg pasta packaging to inactivate microorganisms even-tually contaminating the product during its manipulation. Forthis reason, heat damage of fresh egg pasta can be particularlyintense, involving the development of oxidative reactions andnon-enzymatic browning. Pulsed light could thus represent apromising technology to efficaciously decontaminate theproduct reducing heat damage.

The aim of this study was to provide a global perception ofthe impact of pulsed light technology on the safety and qualityof fresh egg pasta. In particular, we investigated the effect ofincreasing doses of pulsed light on the inactivation of S.enterica and on the development of oxidation, non-enzymatic browning and sensory properties of fresh egg pastajust after preparation and during storage. Data were discussedto identify pulsed light doses allowing product decontamina-tion without impairing overall quality and fresh-like appear-ance of the product.

Materials and Methods

Egg Pasta

Type 00 wheat flour (Triticum aestivum) was obtained from alocal supermarket. New-laid organic eggs were purchased at alocal producer. Egg pasta was prepared using a home-madeprocedure. Whole eggs were mixed (Rowenta KA88, robotcompact 400W+blender, Milano, Italy) with commercial softwheat flour (7:10, w /w) and the crumbly dough obtained waskneaded for 1 min. The dough was then transferred to adomes t i c shee t ing mach ine ( Impe r i a , SP-150 ,Sant'Ambrogio di Torino, Italy), obtaining a 3.5-mm-thickcontinuous sheet. This was then fed eight times through thecalibration rollers, which reduced pasta thickness to approxi-mately 0.8 mm. The pasta sheet was manually cut with a sharpknife into 12.5×4 cm sheets which were packed into 17×10 cm plastic pouches (polycoupled Combiflex PA/PE 090,20/70, Savonitti, Codroipo, Italy) and hermetically sealed(Easy Packer EP-400, Boissy-l'Aillerie, France).

Pulsed Light Treatments

Pulsed light treatments were carried out at 25 °C by using apulsed light mobile decontamination unit (Claranor, Rouaine,France) equipped with four Xenon lamps with emission in the

range 200–1,000 nm (200–400 nm, 41%; 400–700 nm, 51%;and 700–1,000 nm, 8 %). Lamps were positioned at each sideof a quartz plaque held in the centre of the cube-shapedchamber. Samples were placed on the quartz plaque at adistance of 1 cm from the lamps and exposed to increasingdoses of pulsed light from 0.13 to 1.75 J cm−2 pulse−1.Exposure to higher fluence from 3.50 to 26.25 J cm−2 wasobtained by delivering to the sample increasing number ofpulses (2–15), each having a fluence of 1.75 J cm−2 (Table 1).Pulse duration was 50 μs and repetition rate was 0.5 Hz.

Storage

Egg pasta exposed to pulsed light (0, 1.75 and 26.25 J cm−2)were stored under dark at 4 °C for up to 1month. At increasingtimes during storage, samples were analysed for peroxidevalue and absorbance of aqueous extracts.

Bacterial Growth Conditions and Inoculation

S. enterica subsp. enterica 9898 DSMZ (DeutscheSammlung von Mikroorganismen und Zellkulturen) wasused. The strain added with 50 % sterile glycerol as cryopro-tectant was stored at −80 °C in triptone soya broth (TSB;Oxoid, Milano, Italy) until its use. Strains were incubated inTSB at 37 °C for 24 h and subsequently plated onto tryptonesoya agar (Oxoid, Milano, Italy). A single colony was inocu-lated into TSB and incubated at 37 °C for 24 h. A finalconcentration of 108–109 CFU/mL was obtained and diluted1:10 to yield 107–108 (overnight suspension). S. entericasuspension was plated onto egg pasta surface after its sheeting(surface inoculation) or in the dough before its sheeting

Table 1 Effect of increasing doses of pulsed light on Salmonellaenterica 9898 DSMZ inoculated on the surface of egg pasta after sheeting(surface inoculation) or in the dough before sheeting (dough inoculation)

Dose(J/cm2)

Surface inoculation(log CFU/cm2)

Dough inoculation(log CFU/g)

0 4.0±0.1 5.9±0.4

0.13 4.0±0.1 5.6±0.7

0.24 3.9±0.2 5.3±0.4

0.42 2.5±0.1 5.5±0.7

0.70 1.5±0.1 5.2±0.9

1.75 1.5±0.1 5.1±0.6

3.50 <DL 4.9±0.5

5.25 <DL 4.4±0.1

8.75 <DL 3.9±0.1

17.50 <DL 2.6±0.1

26.25 <DL <DL

Data are means of three replicated experiments±SD. DL=0.7 UFC/cm2

on surface; 1.7 log UFC/g in dough

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(dough inoculation). Fifty microliters of S. enterica overnightsuspension was inoculated onto each pasta strip (50 cm2 sur-face) to yield a final concentration of 104–105 CFU/cm2. Fordough inoculation, 150 g of partially kneaded doughwas inoculated with 1.5 mL of S. enterica overnightsuspension to yield 105–106 CFU/g. Subsequently, thedough was further kneaded and sheeted as alreadyreported.

Microbiological Analysis

Surface inoculated egg pasta (100 cm2 surface) was diluted1:5 in maximum recovery diluent (MRD; Oxoid, Milano,Italy). Dough inoculated egg pasta (10 g) was serially dilutedin 40 mL of MRD (Oxoid, Milano, Italy); 0.1-mL aliquots ofappropriate dilutions were plated onto XLD (Oxoid, Milano,Italy) and incubated at 37 °C for 24 h. Preliminary trials werecarried out on non-inoculated pasta samples to check for S.enterica presence. In particular, 25 g of egg pasta were dilutedwith 225 mL of buffered peptone water (BPW, Oxoid,Milano, Italy), homogenised in Stomacher (PBI, Milano,Italy) for 2 min and incubated at 37 °C for 24 h.0.1 mL of BPW was added with 9.9 mL RappaportVassiliadis (RV, Oxoid, Milano, Italy) and incubated at42–43 °C for 18–24 h. Presence/absence of S. entericawas checked by spreading onto XLD plates and incu-bated at 37 °C for 24 h.

Light Transmittance

UV-C light penetration depth in fresh egg pasta was deter-mined photometrically using a portable luminometer (HD-2102.2 Delta Ohm, Padova, Italy) equipped with visible(Vis; LP471 PHOT, Delta Ohm, Padova, Italy) or UV-C(LP471 UVC, Delta Ohm, Padova, Italy) light probes.Particularly, egg pasta with increasing thickness was posi-tioned on the luminometer sensor and exposed to 800 LuxVis light or 17 W/m2 UV-C light. The intensity of the lighttransmitted through egg pasta was measured. The ratio be-tween transmitted light (Io) and incident light (I ) was fitted bythe Beer-Lambert law:

I

I0¼ e−αx ð1Þ

where x is pasta thickness andα is an experimental parameter.The penetration depth (δ ) was defined as the depth at whichthe light irradiance inside the material (I ) fell to 1/e of theintensity of the incident light at its surface (I0). The penetra-tion depth (δ ) was then computed as the reciprocal of theexperimental parameter α .

Temperature

Temperature of egg pasta was measured just after the treat-ment by placing the tip of a thermocouple probe (CrisonThermometer 621, Barcellona, Spain) on the sample surface.Interval time between the end of the pulsed light treatment andsample temperature measurement was less than 30 s.

Colour

Egg pasta colour was assessed by a tristimulus colorimeter(Chromameter-2 Reflectance, Minolta, Osaka, Japan)equipped with a CR-200 measuring head. The instrumentwas standardised against a white tile. Colour was expressedin L*, a* and b* Hunter parameters.

Images

Images of egg pasta were acquired by using an image acqui-sition cabinet (Immagini and Computer, Bareggio, Italy)equipped with a digital camera (EOS 550D, Canon, Milano,Italy). In particular, the digital camera was placed on anadjustable stand positioned 60 cm above a black cardboardbase where the sample was placed. Light was provided by four100W frosted photographic floodlights, in a position allowingminimum shadow and glare. Other camera settings were:shutter time, 1/125 s, F-Number F/6.0 and focal length,60 mm. Images were saved in jpeg format resulting in 3,456×2,304 pixels.

Lipid Extracts Preparation

Lipids were extracted from egg pasta following the method-ology described by Kristensen et al. (2000). About 10 g of eggpasta was transferred to a 100-mL centrifuge tube and 50 mLof methanol-isooctane-ethyl ether solution (1:2:2, v /v ; CarloErba, Milano, Italy) was added. The sample was homogenisedusing a high-speed homogeniser (Polytron, PT 3000,Cinematica, Littau, Switzerland) for 2 min at 9,000 rpm,stirred at room temperature for 20 min at 700 rpm and addedwith anhydrous sodium sulphate (Fluka, Steinheim,Germany). The supernatant was filtered through filter paper(Whatman no. 1) and evaporated at 50 °C and 120 rpm(Laborata 4001, Heidolph, Schwabach, Germany).

Aqueous Extracts Preparation

About 10 g of egg pasta was transferred to a 100-mL centri-fuge tube and 50 mL of deionised water was added. Thesample was homogenised using a high speed homogeniser(Polytron, PT 3000, Cinematica, Littau, Switzerland) for2 min at 9,000 rpm, centrifuged for 5 min at 3,000 rpm(Megafuge 1.0, Hereaus, Osterode, Germany). The

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supernatant was centrifuged for 10 min at 12,500 rpm(Beckman, Avanti J-25, Palo Alto, CA, USA) and then filtered(Econofilter 0.2 μm, Agilent Technologies, Germany).

Absorbance

The absorption spectroscopy measurements of lipid and aque-ous extracts obtained from egg pasta were performed by aUV–Vis spectrophotometer (Cary, Varian, Mulgrave,Australia) at 25 °C with a 1-cm path-length cuvette. Egg pastalipid extracts were diluted 1:500 (w /v ) with isooctane (CarloErba, Milano, Italy). Egg pasta aqueous extracts were diluted1:1 (v /v ) with deionised water.

Peroxide Value

Peroxide value of egg pasta lipids was determined followingthe method of Shanta and Decker (1994). Lipid samples(0.02 g) were weighted into a 20-mL volumetric flask, addedwith 9.8 mL of di-chloromethane/methanol (Carlo Erba,Milano, Italy) solution (7:3, v /v ) and vortexed for 5 s. Foreach sample, 0.05 mL of ferrous ion solution (preparedthrough the mixture of 0.132 M BaCl2 and 0.144 M FeSO4)and 0.05 mL of 3.95 M ammonium thyocianate solution wereadded to the flask and vortexed for 5 s. All reagents were fromCarlo Erba (Milano, Italy). After 5 min of incubation at roomtemperature, absorbance was measured at 510 nm with aspectrophotometer (Cary, Varian, Mulgrave, Australia). Thestandard curve was determined under the same conditionsusing ammonium ferric sulphate (AR grade, Carlo Erba,Milano, Italy) as a standard.

Furan

Furan analysis in egg pasta was carried out by combiningSPME and GC-MS analysis according to slight modificationsexecuted on the method of Bianchi et al. (2006). SPME exper-iments were performed with an 85-mm carboxen-polydimethylsiloxane fibre (Supelco, Bellfonte, PA, USA).Aliquots of 2 g of samples were added with 2 mL of 20 %(w /w) NaCl water solution of d4-furan (internal standard with aconcentration equal to 30 μg/kg) and were placed in 20-mLsealed vials. Incubation time and temperature of the fibre were5 min and 40 °C, respectively. The fibre was then exposed tothe headspace of the vial operating under the optimised extrac-tion conditions, i.e., extraction temperature equal to 40 °C andextraction time equal to 20 min. A constant magnetic stirringwas always applied. Desorption was carried out at 270 °C for2 min. Two fibre blanks were run between each sample toavoid potential “memory effects”. A ultra-Thermo TRACEGC (Thermo Scientific, Waltham, MA, USA) equipped witha DSQ II detector (Thermo Scientific, Waltham, MA, USA)was used for GC-MS analysis. Helium was used as the carrier

gas at a flow rate of 1 mL/min; the gas chromatograph wasoperated in splitless mode with the PTV injector maintained at270 °C and equipped with a PTV multi-baffled liner (i.d.1.5 mm, Thermo Scientific, Waltham, MA, USA). A Rxi-5ms (5 % diphenyl 95 % dimethylpolysiloxane; 30 m×0.25 mm, 0.5 μm) capillary column (Thermo Scientific,Waltham, MA, USA) was used. The following GC oven tem-perature program was applied: 40 °C for 5 min, 15 °C/min to300 °C. Transfer line and source were maintained at 270 and200 °C, respectively. The mass spectrometer was operated inselected-ion monitoring mode (SIM) by recording the currentof the following ions: m/z 68 and 39 for furan and m/z 72 and42 for d4-furan. The corresponding ion ratios were used toconfirm the identification of the analyte. A dwell time of50 ms was used for all the ions. Preliminarily, full-scan EI datawere acquired to determine appropriate masses for SIM underthe following conditions: ionisation energy, 70 eV; mass range,35–150 amu; scan time, 3 scan/s. All the analyses were per-formed by setting the electron multiplier voltage at 1,500 V.Signal acquisition and elaboration were performed using thesoftware Xcalibur (Thermo Scientific, Waltham, MA, USA).

Sensory Analysis

A panel of 10 assessors, equally distributed between males andfemales, of age between 25 and 48, was selected and trained.They all had a minimum of 2 years of experience in discrimi-nation and descriptive sensory methods. For sensory testing,15 g egg pasta was served in odourless plastic dishes at roomtemperature. The panel was allowed to decide through consen-sus which odour descriptor better discriminated samples ex-posed to pulsed light from the fresh one. To this purpose, apreliminary test was performed to identify the off-odour mostlikely to appear as a result of pulsed light treatment. Twosamples (untreated and exposed to 1.75 J/cm2 pulsed light)were presented to the judges, who were asked to write downthe odours which differentiated the samples. The assessorsagreed that sulphur off-odour was the descriptor that bestdiscriminated the treated sample from the fresh one. Assessorswere trained by evaluating different samples using an 8-cmunstructured scale anchored with “nil” and “high,” whichcorresponded to untreated egg pasta or egg pasta exposed to1.75 J/cm2 pulsed light respectively. Assessors were asked toevaluate the intensity of the sulphur off-odour in pulsed lighttreated egg pasta just after its preparation and after cooking for1 min in boiling water containing 0.1 % (w /v) sodium chloride.Samples were indicated by a three-digit code and served to thepanel together with the “nil” and “high” samples.

Statistical Analysis

Results of microbiological analyses are averages of threereplicated samples and are reported as means±SD. Results

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of chemical and physical analyses are averages of at least threemeasurements carried out on different samples and are report-ed as means±SD. Analyses of variance (ANOVA) was per-formed with significance level set to p <0.05 (Statistica forWindows, ver. 5.1, Statsoft Inc. Tulsa, USA, 1997). TheTukey procedure was used to test for differences betweenmeans.

Results and Discussion

Table 1 shows the effect of increasing doses of pulsed light onthe count of S. enterica inoculated on the surface of egg pastaafter sheeting and in the dough before sheeting. With regard tosurface decontamination, following exposure of egg pasta to0.42 J/cm2, 1.5 log reductions of S. enterica were obtained.By increasing the pulsed light dose, S. enterica counts furtherdecreased. In particular, 2.5 Log reductions were obtained byexposing egg pasta to 0.70 and 1.75 J/cm2 pulsed light, whilea count less than the detection limit (0.7 log CFU/cm2) wasfound for doses equal or higher than 3.50 J/cm2. This result,which is consistent with the high sensitivity of S. enterica tolight radiation (Chun et al. 2009; Hierro et al. 2009;Lasagabaster et al. 2011), indicates that pulsed light treatmentsof mild intensity are sufficient to impart the desired germicidaleffect on fresh egg pasta. When S. enterica was inoculated inegg pasta dough before its sheeting, the germicidal effect ofpulsed light was considerably lower. A significant decrease(2.0 log reductions) of S. enterica values was only achieved atdoses equal or higher than 8.75 J/cm2. The exposure of eggpasta to 26.25 J/cm2 pulsed light allowed a microbial countlower than the detection limit (1.7 log CFU/g) to be obtained.The slight effect of pulsed light in decontaminating egg pastadough can be attributed to the fact that light would be able toreach only a thin surface layer of the product. Moreover, localsurface roughness of pasta is expected to shadow eventual

bacterial cells, thus impairing the germicidal effect of pulsedlight.

To estimate how deep light can penetrate into egg pastaleading to inactivation of microbial cells, penetration depth ofVis and UV radiation was evaluated. The latter were chosenbecause most of the light emitted by Xenon lamps is in thesewavelength regions. In particular, egg pasta of increasingthickness was exposed to a source of Vis or UV light andthe intensity of the light transmitted through egg pasta wasmeasured. The ratio between transmitted light (Io) and inci-dent light (I ) is shown as a function of egg pasta thickness inFig. 1. Data were well fitted (r2=0.98) by Eq. (1) with αvalues equal to 0.57 and 24.67 for Vis and UV light, respec-tively. The penetration depth of Vis light was 1.75 mm whilethat of UV light was 0.04mm. This evidence confirms that thegermicidal effect of pulsed light radiation on egg pasta, whichis mainly attributable to its UV-light component, is limited to avery thin surface layer of the product. Light can only affectviability of microbial cells located at the product surface but isineffective if they are internalised. By contrast, Vis light,which is responsible of intense thermal effects, can easily betransmitted though egg pasta potentially causing a tempera-ture increase. Circumstantial evidence of heating was also theoccurrence of moist visually detectable inside the pouches ofegg pasta exposed to the most intense treatment (26.25 J/cm2).It can be inferred that the effect of high doses of pulsed light

0

0.2

0.4

0.6

0.8

1

0 1 2 3 4

I/Io

Thickness (mm)

Vis light

UV light

Fig. 1 Ratio between transmitted (I) and incident (I0) Vis or UV lightthrough egg pasta of increasing thickness

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30

Tem

pera

ture

(°C

)

Dose (J/cm2)

Fig. 2 Temperature of egg pasta exposed to increasing doses of pulsedlight

Table 2 Lightness (L*) and colorimetric parameters a*(green to red) andb* (blue to yellow) of egg pasta exposed to increasing doses of pulsedlight

Dose (J/cm2) L* a* b*

0 82.47±0.38 a −5.32±0.18 a 43.78±2.06 a

1.75 82.43±0.32 a −5.21±0.26 a 42.84±2.02 a

26.25 81.46±0.27 b −4.89±0.22 b 44.19±0.76 a

Means in the same column indicated by a common letter (a and b) are notsignificantly different (p >0.05)

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(>8.75 J/cm2) on S. enterica inoculated in the dough (Table 1)could be the result of pasta heating rather than of the germi-cidal effect of the UV component of pulsed light. To confirmthis hypothesis, temperature of egg pasta exposed to increas-ing doses of pulsed light was measured (Fig. 2). Sampletemperature was found to increase with the increase in thenumber of pulses, never exceeding 60 °C. However, given thelow thickness of egg pasta, temperature equilibration phenom-ena are expected to be not negligible. For this reason, higher orlower local temperatures in egg pasta cannot be excluded inprinciple. The latter could be associated with modification ofdough structure and appearance. No changes in the appear-ance of the product were visually detected when egg pasta wasexposed to 1.75 J/cm2 while at highest dose (26.25 J/cm2) wasassociated with the appearance of areas with low luminosity(images not shown). Colorimetric analysis confirmed that theuntreated control and the sample exposed to 1.75 J/cm2 pre-sented not significantly different colour (Table 2). By contrast,egg pasta submitted to the highest light dose was characterisedby lower values of lightness and a* parameter value neared to

the achromatic point, indicating an overall loss of colourintensity. Colour changes observed in Table 2 could derivefrom photo-induced oxidation of lipids and natural occurringpigments, such as egg carotenoids. To investigate this aspect,lipids were extracted from light treated egg pasta and analysedfor peroxide value and absorbance at 448 nm. The latter wastaken as an index of orange pigments. Analyses were per-formed just after the pulsed light treatment of egg pasta as wellas during its following storage at refrigerated temperature(Figs. 3 and 4). Exposure to pulsed light did not affect theinitial value of peroxides in egg pasta but decreased theirformation rate during storage. Contrarily to what generallyexpected, pulsed light seemed to protect the lipid fraction fromoxidation. It is possible that lipid stability could increase(Fig. 3) to the detriment of the naturally occurring antioxi-dants, such as carotenoids (Fig. 4). In fact, in just treatedsamples, exposure to an intense light dose (26.25 J/cm2)significantly (p <0.05) decreased orange pigments. This in-tense treatment was also associated with a slower decay oforange pigments during storage so that their absorbance wasalways higher than that observed in the untreated control andthe 1.75 J/cm2 treated sample. This evidence suggests thatfurther mechanisms, other than those related to natural

0

10

20

30

40

50

60

0 5 10 15 20 25 30

Pero

xide

val

ue (

mE

q O

/kg

fat)

Time (days)

0 J/cm

1.75 J/cm

26.25 J/cm

2

2

2

Fig. 3 Peroxide value of the lipid fraction extracted from egg pastaexposed to increasing doses of pulsed light and stored at 4 °C

0.06

0.08

0.1

0.12

0.14

0 5 10 15 20 25 30

Abs

(44

8 nm

)

Time (days)

0 J/cm

1.75 J/cm

26.25 J/cm

2

2

2

Fig. 4 Absorbance at 448 nm of the lipid fraction extracted from eggpasta exposed to increasing doses of pulsed light and stored at 4 °C

Table 3 Absorbance at 280 and 380 nm and furan concentration of eggpasta exposed to increasing doses of pulsed light

Dose (J/cm2) Absorbance Furan (μg/kg)

280 nm 380 nm

0 3.558±0.002 c 0.568±0.001 c 10±4 a

1.75 5.932±0.001 a 0.579±0.004 b 14±3 a

26.25 5.232±0.002 b 1.014±0.002 a <LOQ

Means in the same column indicated by a common letter (a–c) are notsignificantly different (p>0.05). LOQ of the validated analytical methodexploited for furan analysis equal to 9 μg kg−1

1

2

3

4

5

6

7

8

9

0 0.5 1 1.5 2

Sulf

ur o

dour

inte

nsity

Dose (J/cm2)

Fresh

Cooked

Fig. 5 Intensity of sulphur off-odour in egg pasta exposed to increasingdoses of pulsed light (fresh) and cooked in boiling water after exposure toincreasing doses of pulsed light (cooked)

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occurring antioxidants, could be involved in the increasedstability of the lipid fraction upon light exposure. The lattercould include the photo-induced development of non-enzymatic browning products with antioxidant activity.Literature evidences actually indicate that this reaction canoccur in egg white upon exposure to both UVand pulsed light(Manzocco et al. 2012, 2013). To verify this hypothesis, theabsorbance at 280 and 380 nm of the aqueous fraction ex-tracted from egg pasta exposed to pulsed light was measured(Table 3). Sample absorbance at these wavelengths wasstrongly affected by the dose of pulsed light. The increase inabsorbance at 280 nm in the sample exposed to 1.75 J/cm2

pulsed light was attributed to the formation of early non-enzymatic browning reaction products. The latter decreasedon further pulsing to produce brown melanoidins absorbing at380 nm. Table 3 also shows that no furan was formed in eggpasta subjected to increasing doses of pulsed light. Althoughno literature is available on the effect of pulsed light on theformation of furan in food, data reported in Table 3 are inagreement with literature results (Fan and Geveke 2007; Buleet al. 2010), where no furan was detected in apple cidersubjected to UV-C light at doses up to 5.76 J/cm2. However,very high furan concentration (1,648 μg/kg) was found inapple juice exposed to 5.76 J/cm2 UV-C (Bule et al. 2010).

The changes in egg pasta absorbance at 280 nm (Table 3)could also be explained based on oxidation of Trp chromo-phores of proteins (Wu et al. 2008). According to the literature(Wu et al. 2008; Manzocco et al. 2012), light would affect thestructure of proteins, inducing disulfide rearrangement andformation of protein radicals. The increased lipid stability ofegg pasta exposed to pulsed light (Fig. 3) could thus beattributed to the interactions between lipid and protein oxida-tion pathways. It can be inferred that, in the presence of a lipidfraction, protein radicals could enter the lipid oxidation path-way, leading to radical termination reactions.

Photo-induced protein modification was also confirmed bythe development of an intense sulphur off-odour in egg pastaexposed to 26.25 J/cm2 pulsed light. To evaluate if the occur-rence of this defect could hinder possible application of pulsedlight to decontaminate egg pasta surface, samples were sub-mitted to sensory analysis. Assessors were asked to evaluatethe intensity of the sulphur odour in egg pasta exposed toincreasing intensity pulsed light. The analyses were performedon just treated sample as well as after cooking in boiling water(Fig. 5). Since the off-odour was clearly evident in the sampleexposed to 26.25 J/cm2, the attention was focused on thesamples exposed to lower doses of light, which howeverresulted effective in decontaminate egg pasta surface(Table 1). It can be observed that the intensity of theoff-odour increased when the sample was exposed to1.75 J/cm2 pulsed light. However, after pasta cooking,the perception of the defect decreased even in the sam-ple exposed to this dose.

Conclusions

Results obtained demonstrate that pulsed light may be suc-cessfully applied to guarantee rapid S. enterica decontamina-tion of egg pasta. However, the germicidal effects strictlydepend on the nature of the contamination. If contaminationoccurs after egg pasta preparation and is mainly located at theproduct surface, microbial inactivation can be achieved byexposure to mild pulsed light treatments (0.70 J/cm2) whichdo not impair product sensory properties. By contrast, higherdoses (>1.75 J/cm2) of pulsed light, required for inactivationof S. enterica contaminating egg pasta ingredients, can jeop-ardise the fresh-like appearance of the product. Doses higherthan 1.75 J/cm2 were not associated with the development of apotentially toxic compound, such as furan, but promoted theformation of non-enzymatic browning products. Based ontheir well-known antioxidant activity, these compounds couldaccount for the increase in the oxidative stability of egg pastalipid fraction.

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