Azzarello, E.

Mancuso, S.

Marone, E.

Redwan, M.

Sabbatini, L.

Taiti, C.

English

Florence Research

149Adv. Hort. Sci., 2018 32(1): 149-153 DOI: 10.13128/ahs-22846Monitoring in real time the changes inVOCs emission in sunflower and extravirgin olive oil upon heating byPTR-ToF-MSL. Sabbatini 1, C. Taiti 1, M. Redwan 1, E. Azzarello 1, E. Marone 2 (*), S.Mancuso 11 Dipartimento di Scienze delle Produzioni Agroalimentari edell’Ambiente, Università degli Studi di Firenze, Viale delle Idee, 30,50019 Sesto Fiorentino (FI), Italy.2 Facoltà di Bioscienze e Tecnologie Agro-Alimentari e Ambientali,Università degli Studi di Teramo, Via R. Balzarini, 1, 64100 Teramo,Italy.Key words: Proton Transfer Reaction Time-of-Flight Mass Spectrometer, proto-nated masses, temperature, vegetable oils, Volatile OrganicCompounds.Abstract: In this work the emission of volatile organic compounds (VOCs) uponthe heating process of an extra virgin olive oil (EVOO) and a high oleic sun-flower oil (SFO) was evaluated in real time by spectrometry. Two tests werecarried out, in the first VOCs emitted from both kinds of oil were measured atroom temperatures (not heated, NH) and at 180°C; in the second test, VOCsemission for selected masses were monitored under increasing temperaturesover time: at room temperature not heated oils (NH), 60, 90, 120, 150, and180°C, respectively. The spectra were acquired using a Proton TransferReaction Time of Flight Mass Spectrometer (PTR-ToF-MS). The total VOCs emis-sion increased at 180°C, determined both by the rise of the amount of com-pounds present in the NH samples and by the formation of new masses gener-ated by oxidative chemical reaction from triglycerides and fatty acids. From theset of results it is evident that a good control of the temperatures can be usefulin reducing the quantities of masses potentially harmful to health in humanfood.1. IntroductionA common worldwide operation extensively used in food preparationis cooking by immersion in hot oil, as for fried and deep fried operations.Types of oils used for fried and deep frying operations vary with differentcultures and are widely used both domestically and commercially. Whenfrying and deep frying are used, fats and oils are carried at elevated tem-(*) Corresponding author: emarone@unite.itCitation:SABBATINI L., TAITI C., REDWAN M., AZZARELLOE., MARONE E., MANCUSO S., 2018 - Monitoringin real time the changes in VOCs emission in sun-flower and extra virgin olive oil upon heating byPTR-ToF-MS. - Adv. Hort. Sci., 32(1): 149-153Copyright:© 2018 Sabbatini L., Taiti C., Redwan M.,Azzarello E., Marone E., Mancuso S. This is anopen access, peer reviewed article published byFirenze University Press(http://www.fupress.net/index.php/ahs/) anddistribuited under the terms of the CreativeCommons Attribution License, which permitsunrestricted use, distribution, and reproductionin any medium, provided the original author andsource are credited.Data Availability Statement:All relevant data are within the paper and itsSupporting Information files.Competing Interests:The authors declare no competing interests.Received for publication 2 December 2017Accepted for publication 23 March 2018AHSAdvances in Horticultural Scienceshort noteAdv. Hort. Sci., 2018 32(1): 149-153150peratures often over 180°C, which in presence ofatmospheric oxygen (between 160 and 240°C) pro-duce many flavor compounds (alkanes, fatty acids,aldehydes, ketones, polycyclic aromatic hydrocar-bons), pleasant or unpleasant, and change their fla-vor stability. The flavor compounds released duringthe heating process are affected by some parameterssuch as  cooking temperature, preparation time,chemical composition of the oils, physical and physic-ochemical constants and the presence of additivesand contaminants (Fullana et al., 2004). The volatilecompounds and sensory characteristics from differ-ent edible oils (Brewer et al., 1999; Katragadda et al.,2010) were altered after intense heating and themain alterations were in the emission of volatilecompounds linked to the oxidation process, com-pounds which are negatively related with the sensoryattributes. In particular, the oxidation process in  oilsmainly lead to the formation of alkyl radicals,alkylperoxyl radicals and decomposition of hydroper-oxide and cause the decay of both their nutritionaland sensory quality (Velasco and Dobarganes, 2002;Silvagni et al., 2012). Moreover,  there are somehuman health risks both linked to oil oxidationsprocess and to many of the originated compoundsreleased by the heating process (Vaclavik et al.,2013).The PTR-ToF-MS tool represents a simple, andhigh-throughput strategy, applicable without anylaborious sample preparations and treatments, par-ticularly suited for analysis in real time of dynamicflavor release (both in vitro and in vivo) from diversefood matrices along the food-to-fork productionchain (Costa et al., 2016).The aims of this study are (1) to test the PTR-ToF-MS as a sampling system for the detection of thereleased compounds from not heated olive and sun-flower oils and to compare with heated oils at theirsmoking point (180°C); (2) to monitor and evaluate inreal-time the VOCs emitted from different oils, uponthe heating from 25°C to 180°C, to understand thedynamic of oxidation phenomena.2. Materials and MethodsVegetable oil materialTwo different types of commercial oils were usedfor this experiment, extra virgin olive oil (EVOO) anda high oleic sunflower oil (SFO). They have differentheating temperatures, this latter (SFO) consideredmore resistant to thermal increases (Smith et al.,2007). Both oils were acquired at the local supermar-ket in Florence city (Italy). The analysis of volatileorganic compounds (VOCs) emitted from both oilsvirgin has been obtained through a PTR-ToF-MS(Ionicon Analytik GmbH, Innsbruck, Austria), which  isan instrument with high resolution mass and sensibil-ity (5-10 ppt) and makes analysis possible withoutany pretreatment of samples. H3O+ was used as areagent ion for the proton transfer reaction.Sample preparation and analysisFirst experiment. For this experiment, 100 ml ofeach type of oil was placed inside a 250 ml Pyrexglass jar, hermetically sealed; the jar’s lid wasequipped with two holes that permitted the insertionof Teflon tubes, which were respectively connectedto a zero-air generator (Peak Scientific instruments,USA) and to the PTR-ToF-MS system. It was essentialto avoid the entry of foreign substances inside thejar, and that was obtained by means of a sealingpaste placed around the lid and the two entry holes.Oil samples were analyzed at two points: Room tem-perature (25°C) and at 180°C.Second experiment. The same steps of the firstexperiment was followed, in addition each oil samplewas heated by using a round electric heating plateand analyzed in real time to verify the VOCs emittedfrom both types of oil at different temperatures:room temperature (25°C), 60, 90, 120, 150, 180°C.Once reached each of the five thermal steps, thetemperature was kept constant for 5 minutes andthen passed to the subsequent thermal step. Theevaluation of the aromatic profile of each oil exam-ined was carried out in real time in order to monitorthe behavior of the various volatile substances duringthe heating process. For each sample the analysislasted for a period of about 50 minutes, recording aspectrum per second for a total of 60 spectra perminute. To determine the achievement of the select-ed temperatures, a trial was performed in parallel; indetails, a thermometer was placed into the jar con-tained 100 ml of different kinds of oil and the timesrequired to reach each temperature, for both sam-ples, were measured as well. The whole analyseswere carried out inside a conditioned room, with aninternal temperature of 25°C in order not to condi-tion the chemical reactions, as they are strongly sen-sitive to variations in temperature and humidity. Thevalue of the white (control) represented by an emptysealant jar was recorded before starting with samplesanalysis, and the volatile profile of the white (control)has always been subtracted from the final value ofSabbatini et al. - VOCs emission in sunflower and extra virgin olive oil upon heating by PTR-TOF-MS151each sample.The VOCs in the headspace were observed bydirect injection into the PTR-ToF-MS and separationof single ions happened accordingly to their mass tocharge (m/z) ratio. All the instrumental parameterswere settled in the following way as in Taiti et al.(2017): drift tube ionization condition at 600 V and acontinuous pressure of 2.20±0.02 mbar; while instru-ment internal calibration was based on: m/z = 29.997(NO+); m/z = 59.049 (C3H7O+) and m/z = 21.022 (H3O+)and was performed off-line. The experiment datawas acquired through the TofDaq software (TofwerkAG, Switzerland) and all spectra were analyzed andacquired using a dead time of 20 ns for the Poissoncorrection and peak extraction following themethodology described in Cappellin et al. (2011),using a modified Gaussian peak shape.3. ResultsThe signal intensity (ncps) generally vary amongdifferent oils. In figure 1 the signal intensity (ncps) ofprotonated m/z detected at 25°C and 180°C in sun-flower oil (SFO) and extra virgin olive oil (EVOO) areclearly indicated. As a general consideration, theintensity of the signals is always higher in EVOO thanin the SFO at the same temperature. At room tem-perature (25°C) the SFO spectrum is smoother, char-acterized by only 16 signals, being a very refined oilcompared to EVOO. The EVOO presents instead 33signals at room temperature when not heated, whichare characteristics of the extra virgin olive oil in gen-eral, even if among them there are some masses thatcould generate off-flavor (m/z = 47.049, m/z =61.028, m/z = 89.060) (Marone et al., 2017; Taiti andMarone, 2017). At temperatures of 180°C, 43 m/zwere measured in EVOO and 39 m/z in SFO, with theformation of 23 new masses generated as a result ofthe high temperature in SFO and 11 new m/z inEVOO, of which only 7 common to both matrices.To better verify the intensity of the signals at tem-peratures below 180°C, some masses of particularrelevance have been selected in SFO and EVOO,found in the most recent literature (Klein et al.,2016). In particular, in the SFO emerge the massesm/z = 57, m/z = 101, and m/z = 113 (Fig. 2); thesemasses are also reported in Klein et al. (2016) as par-ticularly relevant emissions by SFO. For olive oilemerge the masses m/z = 57, m/z = 101, m/z = 115,m/z = 143, also reported in Klein et al. (2016).Moreover, as its peculiar trend, it should be notedthe mass m/z = 45 (Fig. 2), that sharply increases inEVOO starting from 150°C.The emission assessment of the selected massesby PTR-ToF-MS allows to directly examine in realtime the trend of their quantities in SFO and EVOO inrelation to the heating temperatures, avoiding alter-ations due to foods present together with the cook-ing oil, as generally found in the current scientific lit-erature (Ontanón et al., 2013; Klein et al., 2016). Theincreasing temperature determines the increase ofthe emission of the total VOCs produced at eachtemperature point for both SFO and EVOO. Theintensity of VOCs emission by the refined SFO, alwaysappears lower than that of the EVOO. In both oils theincreases are progressive, and related to the increas-ing temperature, in agreement with Katragadda et al.(2010). Both in SFO and EVOO the mass m/z = 57, stillabsent at 90°C, present at 120°C, showed a dramaticincrease at 150°C according to Katragadda et al.(2010), and subsequently restart a trend proportionalto the increase in temperatures. For each matrix allthe other selected masses showed a common trend;Fig. 1 - Signal intensity (ncps) of VOCs compounds in sunfloweroil (SFO) and extra virgin olive oil (EVOO) at 25°C and180°C. Bars represent standard deviations (n = 3).Adv. Hort. Sci., 2018 32(1): 149-153152while they were absent, or present in small quanti-ties, up to a temperature of 90°C, they have a rela-tively modest rise to 120°C, and showed a dramaticincrease from 150°C, according to Nunes et al.(2013). The mass m/z = 57, always absent in theunheated oils, would derive from the dehydration ofglycerol subjected to high temperatures (Klein et al.,2016), and this would be a phenomenon common toall vegetable oils: the aldehydes that may be presentin virgin olive oils as a result of a natural enzymaticoxidation of polyunsaturated fatty acids(LypOXigenase cascade, LOX) increase due to thetemperature through a chemical oxidative reaction ofthe same polyunsaturated fatty acids (Muik et al.,2005).4. Discussion and ConclusionsThe PTR-ToF-MS tool represents a simple, andhigh-throughput strategy, applicable without anylaborious sample preparations and treatments, forthe real-time detection of oxidative changes occurredduring the heating process of both vegetable oils.There are numerous studies that examine the qualityof the oil, as well as its composition and characteris-tics during the heating or frying process; neverthe-less, a fewer number of studies examine the compo-sition of the fumes generated during this process.In this work, it is pointed out that EVOO emissionsare always higher than those of the SFO; the effect ofthe heating causes an increase in the emission of themasses present at the origin and the generation ofnew compounds, deriving from transformations oftriglycerides and above all of the polyunsaturatedfatty acids (Moreno et al., 1999). In particular, thetrend of emissions in relation to the temperature hasbeen highlighted for some selected masses, and it isclear that change due to chemical oxidation occurbetween 120 and 150°C, temperatures above whichthe production of volatiles increases enormously forall the examined masses. Since the increase in oiltemperature proportionally increases the emission ofVOCs, including some compounds that could be con-sidered as pollutants, it is clear that an accurate con-trol of the temperatures of  oils used for frying foodis important for the industry and for the home cook-ing. Many VOCs depend on the temperature, emis-sions at temperatures below the smoke point will beactually reduced. Some compounds, such as massm/z = 57, start to form consistently already at rela-tively low temperatures (150°C). It should be notedthat in the case of EVOO, masses of naturally occur-ring compounds are also very high, as they arederived from an oxidative process linked to enzymat-ic reactions of the polyunsaturated fatty acids(LipOXygenase pathway, LOX) (Campestre et al.,2017). The increase determined by high tempera-tures is no longer enzymatic but chemical oxidative.Further studies are needed to deepen the knowledgeon the effect of heating temperature in the forma-tion of compounds potentially harmful to humanhealth, in order to reduce the effect of pollution notonly at commercial but also at the domestic level, forthe daily use of fried oils.ReferencesBREWER M.S., VEGA J.D., PERKINS E.G., 1999 - Volatilecompounds and sensory characteristics of frying fats. -J. 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Monitoring in real time the changes in VOCs emission in sunflower and extra virgin olive oil upon heating by PTR-ToF-MS

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Monitoring in real time the changes in VOCs emission in sunflower and extra virgin olive oil upon heating by PTR-ToF-MS

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