Optimisation of pressurised liquid extraction (PLE) for rapid and efficient extraction of...

Food Chemistry 157 (2014) 470–475

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Food Chemistry

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Optimisation of pressurised liquid extraction (PLE) for rapid and efficientextraction of superficial and total mineral oil contamination from dryfoods

http://dx.doi.org/10.1016/j.foodchem.2014.02.0710308-8146/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Tel.: +39 0432 558146; fax: +39 0432 558130.E-mail address: sabrina.moret@uniud.it (S. Moret).

Sabrina Moret a,⇑, Marianna Scolaro a, Laura Barp a, Giorgia Purcaro a, Maren Sander b, Lanfranco S. Conte a

a Department of Food Science, University of Udine, Via Sondrio 2A, 33100 Udine, Italyb BÜCHI Labortechnik AG, Meierseggstrasse 40, 9230 Flawil, Switzerland

a r t i c l e i n f o a b s t r a c t

Article history:Received 10 August 2013Received in revised form 17 January 2014Accepted 17 February 2014Available online 26 February 2014

Keywords:Pressurised liquid extraction (PLE)Mineral oil saturated hydrocarbons (MOSH)Mineral oil aromatic hydrocarbons (MOAH)Food contaminationOn-line LC–GC

Pressurised liquid extraction (PLE) represents a powerful technique which can be conveniently used forrapid extraction of mineral oil saturated (MOSH) and aromatic hydrocarbons (MOAH) from dry foodswith a low fat content, such as semolina pasta, rice, and other cereals. Two different PLE methods, onefor rapid determination of superficial contamination mainly from the packaging, the other for efficientextraction of total contamination from different sources, have been developed and optimised. The twomethods presented good performance characteristics in terms of repeatability (relative standard devia-tion lower than 5%) and recoveries (higher than 95%). To show their potentiality, the two methods havebeen applied in combination on semolina pasta and rice packaged in direct contact with recycled card-board. In the case of semolina pasta it was possible to discriminate between superficial contaminationcoming from the packaging, and pre-existing contamination (firmly enclosed into the matrix).

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Mineral oils are complex mixtures of hydrocarbons of petrogen-ic origin comprising saturated hydrocarbons (named MOSH) whichinclude linear, branched and cyclic compounds, as well as aromatichydrocarbons (MOAH), mainly alkylated.

Food can be contaminated with mineral oil from different sources(Biedermann & Grob, 2012a; Droz & Grob, 1997; Grob, Artho, Bieder-mann, & Egli, 1991; Grob, Huber, Boderius, & Bronz, 1997; Moret,Grob, & Conte, 1997; Moret, Populin, Conte, Grob, & Neukom,2003). Foodstuffs of vegetable origin present a background contami-nation reflecting environmental contamination (Neukom, Grob, Bie-dermann, & Noti, 2002). Processed food can be contaminated withfood grade mineral oils (treated to eliminate MOAH) largely used infood industry as lubricating, release agents, dust suppressants forgrain or animal feed, protective coatings for raw fruits and vegetablesand in some cases as ingredients (EFSA, 2012). Other importantsources of contamination are food contact materials and particularlyrecycled paperboard used as food packaging and mineral oil basedprinting inks (in these cases 15–35% of the contamination is repre-sented by MOAH) (Biedermann & Grob, 2012a).

MOSH from C16 to C35 may accumulate and cause microgran-ulomas in several tissues (lymph nodes, spleen and liver). In 2002,the Joint FAO/WHO Expert Committee on Food Additives (JECFA)set a temporary group ADI value of 0–0.01 mg kg�1 body weight(b.w.) for medium and low viscosity white mineral oils (class IIand III) in the same volatility range as those migrated from card-board (JECFA, 2002). As data supporting the establishment of a fullADI had not been made available, the previously established tem-porary group ADI has been recently withdrawn (JECFA, 2012).

In 2012 the EFSA Panel on Contaminants in the Food Chain (CON-TAM) expressed a Scientific Opinion on Mineral Oil Hydrocarbons inFood, concluding that background exposure to MOSH (C16–C35) viafood in Europe is of potential concern (EFSA, 2012). Exposure toMOAH through food was also considered of concern due to the car-cinogenic risk associated with this class of hydrocarbons.

Rapid mineral oil determination can be accomplished using on-line LC–GC–FID (Biedermann, Fieseler, & Grob, 2009; Biedermann& Grob, 2012b; Purcaro, Moret, & Conte, 2012, 2013; Tranchidaet al., 2011) or off-line SPE–GC–FID (Fiselier et al., 2013; Moret,Barp, Grob, & Conte, 2011; Moret, Barp, Purcaro, & Conte, 2012).On-line methods are preferable, when available, as they allow di-rect injection of the sample extract, automating the analysis andminimizing sample manipulation.

Depending on the food composition and source of contamina-tion, a complete extraction of mineral oil from food can be

S. Moret et al. / Food Chemistry 157 (2014) 470–475 471

demanding. Extraction of mineral oil migrated from packaging intolow fat dry foods, such as pasta or grain cereals, does not representa difficult task since the contamination probably remains on thesurface. In most cases extraction was performed with hexane over-night on ground samples (Biedermann-Brem & Grob, 2011; Voll-mer et al., 2011) but it has been verified that similar results canbe obtained by extracting the unground sample (unpublisheddata).

Extraction of pre-existing contamination from different sourcesis, instead, more difficult, since the contaminants can be firmly in-cluded into the matrix. Soaking with hot water (80 �C for 1 h), fol-lowed by a two-step extraction, first with ethanol (1 h) toexchange the water in the particles by ethanol, and then with hex-ane overnight, allows to obtain complete MOSH and MOAH recov-eries (Biedermann-Brem & Grob, 2011; EFSA, 2012), but requires along time and intense sample manipulation.

Pressurised liquid extraction (PLE), sometimes referred to alsoas pressurised solvent extraction (PSE), is a well know extractiontechnique exploiting the enhanced extraction power of a solventtaken at high temperature under pressure. Compared to classicalsolvent extraction, PLE allows to perform efficient and rapidextractions at high temperature an high pressure, minimizing sol-vent consumption and sample manipulation. To obtain goodextraction efficiencies, a number of parameters such as type of sol-vent, extraction temperature, extraction time, number of cyclesand wash with solvent have to be optimised. Recently a PLE meth-od for extraction of MOSH and MOAH from cardboard and papersamples has been developed and validated (Moret et al., 2013).

The aim and the novelty of the present work was the develop-ment and optimisation of PLE for rapid monitoring of mineral oilcontamination in dry foods with a low fat content (frequentlypackaged in direct contact with cardboard packaging). In particulartwo different methods with different selectivity where optimised:one for extraction of mineral oil migrated from packaging and an-other for quantitative extraction of total contamination from dif-ferent sources. Potentialities of the proposed methods were thendemonstrated by applying them in combination on semolina pastaand rice packaged in recycled cardboard.

2. Experimental

2.1. Reagents and standards

Ethanol (HPLC grade), n-hexane and acetone were purchasedfrom Sigma–Aldrich (Milan, Italy). Hexane and acetone were dis-tilled before use. Internal standards were purchased from Supelco(Milan, Italy). The working standard solution was prepared by mix-ing 5-a-cholestane (Cho, 0.6 mg mL�1), n-C11 (0.3 mg mL�1), n-C13 (0.15 mg mL�1), cyclohexyl cyclohexane (CyCy, 0.3 mg mL�1),n-pentyl benzene (5B, 0.30 mg mL�1), 1-methyl naphthalene (1-MN, 0.30 mg mL�1), 2-methylnaphthalene (2-MN, 0.30 mg mL�1),tri-tert-butyl benzene (TBB, 0.3 mg mL�1) and perylene (Per,0.6 mg mL�1) in toluene.

2.2. Samples

Dry food samples (pasta and rice) were purchased from themarket. Some samples were part of a project to study MOSH andMOAH migration from packaging into pasta during shelf-life, underdifferent storage conditions. Paperboard samples used for migra-tion tests were directly purchased from the producer or were fur-nished by the final user.

2.3. Extraction

PLE was carried out using a SpeedExtractor E-916 (BÜCHILabortechnik AG, Flawil, Switzerland) equipped with six 10-mLstainless steel extraction cells. Pre-washed cellulose filters wereplaced at the exit of the cells to prevent clogging of the metal frit.

2.3.1. PLE method A (for contamination coming from the packaging)The food sample (about 8 g of small size pasta or rice) was di-

rectly loaded into a 10 mL PLE cell (without using any dispersingagent). Large size pasta would need to be reduced to small pieces.Prior to extraction, 8 lL of the internal standard working solutionwas added into the extraction cell (filled with the sample) forquantification and to verify LC–GC performance and completeMOSH and MOAH separation as described by Biedermann andGrob (2012b).

PLE optimisation was carried out on pasta samples stored fordifferent time (1–9 months) in boxes of recycled cardboard atambient temperature. After packaging, the boxes were wrappedin aluminium to avoid exchange with the external environment.Before packaging, the pasta sample had no detectable contamina-tion (by applying PLE method A). Hexane was chosen as the extrac-tion solvent since it was previously used for classical solventextraction (Vollmer et al., 2011) and the extract was suitable for di-rect injection.

Different extraction temperatures (80, 100 and 120 �C), andextraction time (5 and 10 min) were tested for method optimisa-tion. A t-test was performed to compare the results obtained fromdifferent tested conditions. Final conditions are reported in Table 1together with performance characteristics.

Repeatability was assessed with 6 replicate analyses carried outon a pasta sample stored for 9 months in recycled cardboard.Recoveries were assessed in triplicate by comparing the responseobtained with an additional extraction cycle with those obtainedby applying the optimised method.

The extract, collected in a 60-mL glass vial, was left to rest for atleast 15 min or, alternatively, centrifuged to separate trace of waterextracted during PLE and directly injected into the LC–GC withoutpre-concentration.

2.3.2. PLE Method B (for total contamination from different sources)The extraction cell was filled, bottom to top, with a 5 g of fat

free quartz sand (0.3–0.9 mm) (Büchi), 2.0 g of ground sample(IKA A10 analytical mill) mixed with 6 g of sand, added with inter-nal standard (1 lL per g of sample) and sand to fill the void volume.Alternatively, the standard can be added directly in the collectingvial. Different extraction solvents such as hexane, acetone, hex-ane/acetone 1:1 (v/v), hexane/ethanol 1:1 (v/v), extraction temper-ature (100, 120 and 150 �C), extraction time (5 and 10 min),number of cycles (1–3), and wash with solvent, were tested induplicate for method optimisation. A t-test was performed to com-pare the results obtained.

At the end of the 2-cycle extraction, the extract (about 15 mL)was collected in 60-mL vial, added with water (about 30 mL) toseparate the ethanol from the hexane. To facilitate phase separa-tion avoiding formation of an emulsion, the extract was main-tained at �20 �C for about 20 min. An aliquot of the hexaneextract was used for LC–GC analysis.

Repeatability (6 replicates) was assessed on two pasta sampleswith different contamination profiles and different contaminationlevels (low and high). Recoveries were checked in duplicate onthree samples with different contamination profiles by comparingthe response obtained with an additional cycle, with those ob-tained by applying the optimised method. Optimised extractionconditions and performance characteristics are reported in Table 1.

Table 1Optimised extraction conditions and performance characteristics for PLE methods Aand B (SpeedExtractor E-916, 6 positions).

PLE method A PLE method B

Temperature 100 �C 100 �CPressure 100 bar 100 barCells (volume) 10 mL 10 mLSolvent Hexane Hexane/ethanol 1:1 (v/

v)Cycles (number) 1 2

Heat up 1 min 1 minHold time 5 min 5 minDischarge 2 min 2 min

Flush with solvent 1800 0 at 2 mL min�1 NoFlush with gas (N2) 1 min 1 minAmount of sample 8 g 2 g (ground)Total solvent

consumption13 mL 15 mL

Total extraction time <20 min (washincluded)

28 min

Limit of detection (mg/kg)*

0.1 0.2

Average recovery (%) 97 96Repeatability (RSD%;

n = 6)4.5 5.9

* 4 mL of sample extract concentrated at 1 mL; injection volume: 100 lL.

472 S. Moret et al. / Food Chemistry 157 (2014) 470–475

For comparison purposes, the same sample used for methodoptimisation (high contamination level) was extracted using themethod proposed by Biedermann-Brem and Grob (2011), as wellas using overnight extraction with hexane (Vollmer et al., 2011),and the results were compared. Briefly, the dry sample was soakedin hot water (1 h), extracted first with ethanol (1 h contact) andthen overnight with hexane (after removing the ethanol phase).The two extracts were then combined and added with water toseparate the hexane extract from the ethanol. Overnight extractionwas carried out at ambient temperature under magnetic stirring on5 g of the ground sample which was extracted with 10 mL ofhexane.

2.3.3. Combined PLE methodsTo evidence deep contamination firmly enclosed into the matrix

(also in the presence of mineral oil migrated from the packaging),the sample which underwent PLE method A, was recovered fromthe extraction cell, ground, and, an aliquot (2 g) was re-extractedby using PLE method B.

2.4. LC–GC analysis

The LC–GC instrument (LC–GC 9000, Brechbühler, Zurich, Swit-zerland) consisted of a Phoenix 40 with three syringe LC pumpsand four switching valves and an UV/VIS detector (UV-2070 Plus,Jasco, Japan). The autosampler was a PAL LHS2-xt Combi PAL(Zwingen, Switzerland). The LC column was a 25 cm � 2.1 mm i.dLichrospher Si 60, 5 lm (DGB, Schlossboeckelheim, Germany).The GC was a Trace GC Ultra from Thermo Scientific (Milan, Italy).

A gradient, starting with hexane (0.1 min) and reaching 30% ofdichloromethane (at 300 lL/min) in 0.5 min, was used to elutethe MOSH (from 2.0 to 3.5 min) and the MOAH (from 4 to5.5 min) as described by Biedermann-Brem and Grob (2011).

LC–GC transfer occurred through the Y-interface based on theretention gap technique and partially concurrent eluent evapora-tion (Biedermann et al., 2009). A 10 m � 0.53 mm i.d. uncoated,deactivated precolumn was followed by a steel T-piece union con-nected to the solvent vapor exit (SVE) and a 15 m � 0.25 mm i.d.separation column coated with a 0.15 lm film of PS-255 (1% Vinyl,99% Methyl Polysiloxane) (Mega, Italy). A rapid oven gradient(40 �C/min) starting from 55 �C up to 350 �C was used for GC

analysis (Barp, Purcaro, Moret, & Conte, 2013). The FID and theSVE were heated at 360 and 140 �C, respectively. After the transfer,the LC column was backflushed (dichloromethane) and recondi-tioned prior to the subsequent injection.

Data were acquired and processed by the Exachrom software(Brechbuhler, Switzerland). The MOSH area was determined bythe integration of the whole hump of largely unresolved peaks, de-tracted of the endogenous n-alkanes. All sharp peaks standing onthe top of the MOAH hump were subtracted from the total area.

Linearity of the analytical method was previously verified byBarp et al. (2013) at 5 levels in triplicate (in the range 1–50 lg/mL) with both paraffin oil (R2 = 0.9995) and offset printing ink(R2 = 0.9993). Limit of quantification around 0.1–0.2 mg/kg canbe easily reached by concentrating 4 mL of the sample extract to1 mL before injection.

3. Results and discussion

3.1. Optimisation and performance of PLE method A

For method optimisation, different extraction conditions weretested on selected samples of small size pasta packaged in directcontact with recycled cardboard.

No significant differences on extraction efficiencies were ob-served when increasing the temperature from 80 to 120 �C andthe extraction time from 5 to 10 min (p > 0.05). Fig. 1a shows anoverlay of the MOSH and MOAH traces obtained at different tem-peratures and extraction times for 3 different aliquots of the samepasta sample stored for 3 months in recycled paperboard box (onthe left). Extraction yields with 1 cycle at 100 �C for 5 min werenot quantitative, but a washing with hexane at 2 mL/min for2.5 min (5 mL) performed at the end of the cycle, allowed to reachpractically quantitative recoveries. Fig. 1b shows the traces ob-tained with the optimised method (including a solvent wash)and with a further extraction cycle (collected separately) whichcontained less than 3% of the total contamination (average recov-ery 97%).

Repeatability was assessed with 6 replicate analyses carried outon a pasta sample stored for 9 months in recycled cardboard. A rel-ative standard deviation lower than 5% was found for both MOSHand MOAH.

3.2. Optimisation and performance of PLE method B

PLE optimisation was carried out on pasta samples naturallycontaminated with mineral oil of difficult extractability from dif-ferent sources (not from the packaging).

To obtain high extraction efficiency, samples processed withPLE have to be ground to a fine powder (the smaller the particles,the larger the relative surface area, and thus the more efficient theextraction) and mixed with a dispersive agent to increase superfi-cial area exposed to the solvent. To avoid blank problems the sandwas pre-washed with hexane before use (100 �C, 100 bar for5 min).

Different extraction solvents, namely: hexane, acetone, hexane/acetone 1:1 (v/v) and hexane/ethanol 1:1 (v/v), were tested on thesame pasta sample, contaminated with mineral oil (MOSH) proba-bly from 2 different sources (two humps, the first one centred onC21, the second one centred on C33). Fig. 2a shows the LC–GCtraces obtained performing a two-cycle extraction with the differ-ent solvents (100 �C, 5 min at 100 bar).

As visible in the figure, hexane gave the worst result, while themixture hexane/ethanol 1:1 (v/v) gave the best results. Based onthese results, the mixture hexane/ethanol 1:1 (v/v) was chosenas extraction solvent. This solvent mixture well exploits the swell-

Hexane1 cycle, 100 bar

80 °C, 5 min 100 °C, 5 min 100 °C, 10 min 120 °C, 5 min

PLE method A(1 cycleHex/EtOH +solvent wash)

a b

Additionalextraction cycle

1284 8 min

Fig. 1. Optimisation of PLE method A (contamination from packaging). LC–GC traces (MOSH) of the same pasta sample packaged for 3-months in recycled cardboard,obtained by performing (a) a one-cycle extraction with hexane (100 bar) at different extraction times and temperatures, and (b) by applying the optimised PLE method A(including a solvent wash) and an additional separate extraction cycle (100 bar, 100 �C, 5 min).

S. Moret et al. / Food Chemistry 157 (2014) 470–475 473

ing power of the ethanol towards starch (favouring the release ofphysically entrapped hydrocarbons) and its ability to denature pro-teins (which, in its folded structure, could retain some fat andhence lipophilic contaminants), as well as the extracting powerof hexane towards hydrocarbons.

To verify the number of extraction cycles needed to achieve sat-isfactory extraction recovery, the same pasta sample was pro-cessed by performing (in duplicate) 3 consecutive cycles(collected separately). Fig. 2b shows an overlay of the GC traces ob-tained. This trial demonstrated that a two-cycle extraction isneeded to obtain good recoveries.

Different extraction temperatures (100, 120 and 150 �C) werethen tested in triplicate on the same pasta sample. Comparable re-sponses were obtained by increasing the extraction temperaturefrom 100 to 120 �C, while, even if not statistically relevant(p > 0.05), a slight decrease, was observed at 150 �C.

Good repeatability (relative standard deviation lower than 6%)was obtained with optimised conditions (Table 1) for both samplesconsidered: low (0.8 mg kg�1) and high (13.7 mg kg�1) contamina-tion level.

Extraction recoveries, assessed (in duplicate) on three differentsamples contaminated with mineral oil from different sources (dif-ferent LC–GC profiles), were higher than 95%.

hexane/aceton

acetone

hexane

hexane/ethanol (1:1)

8 12

a

Fig. 2. Optimisation of PLE method B for total contamination: (a) overlay of the LC–GC trasources (not from the packaging), obtained by performing a 2-cycle extraction (100 bar,traces (MOSH) obtained by performing three consecutives extraction cycles (100 bar, 100(not from the packaging).

3.2.1. Comparison with other extraction methodsResults obtained with the optimised method, were then com-

pared with those obtained (in duplicate) by applying overnightextraction with hexane (on ground sample) and with the methodproposed by Biedermann-Brem and Grob (2011). Fig. 3 shows anoverlay of the GC traces obtained by applying the 3 procedureson different aliquots of the same pasta sample. All sample extractswere concentrated in order to inject an amount corresponding to200 mg of sample.

It was confirmed that, in contrast to overnight extraction withhexane, the optimised PLE method allows for complete extractionof mineral oil and gives results well in agreement with those ob-tained by applying the method proposed by Biedermann-Bremand Grob (2011) (p > 0.05), which is more time- and solvent-consuming.

3.3. Examples of application to dry food samples

To show the potentiality of the two PLE methods, they were ap-plied (alone or in combination) to a semolina pasta with a pre-existing contamination of 0.8 mg kg�1, before and after a one-and a nine-month storage in recycled cardboard boxes wrappedwith aluminium. These samples are part of a project whose resultswill be published in a forthcoming publication. Before injection,

e (1:1)

hexane/ethanol (1:1)

3° cycle

1° cycle

2° cycle

8 12 min

b

ces (MOSH) of the same pasta sample contaminated with mineral oil from different100 �C, 5 min) with different extraction solvents or mixtures; (b) overlay of LC–GC�C, 5 min) on a pasta sample contaminated with mineral oil from different sources

soaking with hot water + ethanol extraction (1h) hexane extraction overnight

hexane extraction overnight

4 8 12 16 min

PLE method Bhexane/ethanol 1:1

4 84 1284

Fig. 3. Comparison with methods based on classical solvent extraction. Overlay ofLC–GC traces (MOSH) obtained by extracting the same sample contaminated withmineral oil from different sources with the optimised PLE method B, with overnightextraction with hexane (under magnetic stirring) and with the method proposed byBiedermann-Brem and Grob (2011).

474 S. Moret et al. / Food Chemistry 157 (2014) 470–475

the volume of the extracts obtained with the two methods wereadjusted in order to inject a volume corresponding to the samesample amount (200 mg). Fig. 4a and b shows respectively an over-lay of the MOSH and MOAH traces obtained with PLE method A.The pasta sample before packaging (T0) showed no detectable con-tamination when applying method A. Most of the contaminationfrom the packaging migrated after the first month of contact (T1had 3.4 and 0.5 mg kg�1 of MOSH and MOAH, respectively), andreached higher level after 9 months (T9 had 4.6 and 0.7 mg kg�1

of MOSH and MOAH, respectively). Fig. 4c shows an overlay ob-tained with PLE method B (total contamination). The presence ofa pre-existing contamination (not extracted with PLE method A)is well evident in sample T0 (0.8 mg kg�1 of MOSH), but also in

4 8

T9

T0

T1

T0

T1

T9

PLE A

PLE B (total contaminatio

MOS

MOS

a

c

Fig. 4. Application of optimised PLE methods to semolina pasta before packaging (T0) atraces obtained with optimised PLE method A for selective determination of mineral oil mtraces obtained with optimised PLE method B for total contamination, and (d) MOSH tramethod PLE B after PLE A (d).

sample T1 (4.2 mg kg�1 of MOSH) and T9 (5.3 mg kg�1 of MOSH).These results show as, in this case, PLE method A was selective onlytowards mineral oil migrated from the packaging which remainedon the surface of the product, while PLE method B allowed forextracting total contamination from different sources (pre-existingcontamination as well as contamination from the packaging). Byapplying PLE method B on residual pasta which already underwentPLE method A, it was possible to eliminate the contribution of min-eral hydrocarbons migrated from the packaging quantifying thepre-existing contamination (see Fig. 4d). This could be not possiblein the presence of superficial contamination from different sources,or when part of the pre-existing contamination is not firmly in-cluded into the matrix.

Furthermore, it was found that a small amount of the contam-ination from the packaging remained in the sample after applyingPLE method A. This amount slowly increased with storage time,indicating that only a negligible part of the contamination fromthe packaging penetrated deeply into the sample and/or interactedwith sample components, becoming less available to extractionwith PLE method A.

As an additional example, two rice samples (one of which par-boiled), with no detectable contamination (no pre-existing con-tamination), were contaminated by a 10-day contact withprinted recycled cardboard at 40 �C, then separated from the card-board, wrapped in aluminium, and analysed with both PLE meth-ods after a 6-month storage at ambient temperature. Also in thiscase the samples which underwent PLE method A were groundand re-extracted with PLE method B.

Fig. 5 shows an overlay of the MOSH traces obtained for the par-boiled rice by applying on three different aliquots of the same sam-ple: PLE method A, PLE method B, as well as both PLE methods (Bafter A). Results again demonstrated that, also after a prolongedstorage at ambient temperature, PLE method A allows for a total

12 8 12 min

T0

T1T9

T0T1T9

n) PLE B after PLE A

MOAH

H MOSH

HPLE A

Pre-existingcontamination

Migrated frompackaging

d

b

nd after one (T1) and nine (T9) months of storage in recycled cardboard: (a) MOSHigrated from the packaging, (b) MOAH traces obtained with PLE method A, (c) MOSHces obtained for selective determination of pre-existing contamination by applying

4 8 12 min

PLE method A

PLE method B(shifted trace)

PLE method Bafter PLE A

Fig. 5. Application of optimised PLE methods to a rice sample with no pre-existingcontamination, maintained for 10 day at 40 �C in contact with recycled paperboardand then stored without the packaging at ambient temperature for 6 months.

S. Moret et al. / Food Chemistry 157 (2014) 470–475 475

extraction of mineral oil migrated from the packaging (less than 3%of the total contamination remained in the product after extractionwith PLE method A). Similar results were found with the other ricesample.

4. Conclusions

Efficient and rapid extraction of mineral oil from dry food rep-resents an important goal for control laboratories as well as re-search purposes.

Two PLE methods, one for selective extraction of superficialcontamination (mainly migrated from the packaging), and theother for total contamination from different sources have beendeveloped and optimised.

Some examples shows that, when used in combination on cer-tain pasta samples, the two methods may be helpful to understandhow the contamination is distributed in the product, and, in somecases, allow to discriminate between pre-existing contaminationand contamination migrated from the packaging. Compared toclassical solvent extraction previously described, the PLE approachrequires less sample manipulation and is less time- and solvent-consuming.

Acknowledgements

This work was made possible also thanks to the contribution ofthe Italian Ministry for the University and Research (MIUR) with aFIRB ‘‘Futuro in Ricerca’’ Project n. RBFR10GSJK ‘‘Tecniche Anali-tiche Avanzate per l’Analisi dei Contaminanti negli Alimenti’’.

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