Food Additives and Contaminants ISSN: 0265-203X (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/tfac19 Study of acrylamide in coffee using an improved liquid chromatography mass spectrometry method: Investigation of colour changes and acrylamide formation in coffee during roasting Hamide Z. Şenyuva & Vural Gökmen To cite this article: Hamide Z. Şenyuva & Vural Gökmen (2005) Study of acrylamide in coffee using an improved liquid chromatography mass spectrometry method: Investigation of colour changes and acrylamide formation in coffee during roasting, Food Additives and Contaminants, 22:3, 214-220, DOI: 10.1080/02652030500109834 To link to this article: https://doi.org/10.1080/02652030500109834 Published online: 20 Feb 2007. Submit your article to this journal Article views: 5678 View related articles Citing articles: 12 View citing articles Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=tfac19 Food Additives and Contaminants, March 2005; 22(3): 214–220 Study of acrylamide in coffee using an improved liquid chromatography mass spectrometry method: Investigation of colour changes and acrylamide formation in coffee during roasting HAMIDE Z. ŞENYUVA1, & VURAL GÖKMEN2 1 Ankara Test and Analysis Laboratory, Scientific and Technical Research Council of Turkey, Ankara 06330, Turkey, and 2Food Engineering Department, Hacettepe University, Ankara, Turkey (Received 16 January 2005; revised 25 February 2005; accepted 28 February 2005) Abstract An improved analytical method for the determination of acrylamide in coffee is described using liquid chromatography coupled to mass spectrometric detection (LC-MS). A variety of instant, ground and laboratory roasted coffee samples were analysed using this method. The sample preparation entails extraction of acrylamide with methanol, purification with Carrez I and II solutions, evaporation and solvent change to water, and clean-up with an Oasis HLB solid-phase extraction (SPE) cartridge. The chromatographic conditions allowed separation of acrylamide and the remaining matrix co-extractives with accurate and precise quantification of acrylamide during MS detection in SIM mode. Recoveries for the spiking levels of 50, 100, 250 and 500 mg/kg ranged between 99 and 100% with relative standard deviations of less than 2%. The effects of roasting on the formation of acrylamide and colour development were also investigated at 150, 200 and 225 C. Change in the CIE (Commission Internationale de l’Eclairage) a* colour value was found to show a good correlation with the change in acrylamide. CIE a* and acrylamide data was fitted to a non-linear logarithmic function for the estimation of acrylamide level in coffee. Measured acrylamide levels in commercial roasted coffees compared well with the predicted acrylamide levels from the CIE a* values. Keywords: Acrylamide, coffee, colour, roasting Introduction Since the discovery of acrylamide in foods was made public in April 2002 (Tareke et al. 2002), several research groups have been involved in developing methods to reliably quantify acrylamide at relatively low levels in a large variety of different foodstuffs. The general findings are that acrylamide will invariably be found in heated carbohydrate foods. One possible pathway to the formation of acrylamide in some foods is probably via the Maillard reaction, which involves the reaction of an amino acid with a carbonyl compound during heating (Mottram et al. 2002; Stadler et al. 2002). The high consumption of coffee in many countries makes it a potentially significant source of daily exposure to acrylamide. Due to the use of roasted coffee beans in making coffee, the probability of significant levels of acrylamide being present was considered to be high. The chemistry of coffee roasting is complex and still not completely understood. Aromatics, acids, and other flavor components are either created, balanced, or altered in a way that should augment the flavor, acidity, after taste and body of the coffee during roasting. The roasting temperature determines the specific types of chemical reactions that occur in coffee. In addition to desired characteristics, undesirable changes such as the formation of acrylamide should also be considered in this process. Coffee, as a source of acrylamide, needs to be investigated in depth to determine the effects of roasting conditions on acrylamide levels. Analysis of acrylamide in coffee is challenging because of co-extractives and the inherent difficulties in confirming a low molecular mass (MW 71) compound in a complex matrix. Most of the methods published so far are based on either GC-MS (Castle et al. 1991, Biedermann et al. 2002, Ono et al. 2003, Nemoto et al. 2002) or LC-MS (Rosén and Hellenäs 2002; Ahn et al. 2002; Zyzak et al. 2003; Becalski et al. 2003; Roach et al. 2003; Jezussek and Schieberle 2003; Riediker and Stadler 2003) techniques, with comparable performance of two approaches. The Correspondence: Hamide Şenyuva, Email: [email protected] ISSN 0265–203X print/ISSN 1464–5122 online ß 2005 Taylor & Francis Group Ltd DOI: 10.1080/02652030500109834 Study of acrylamide in coffee results of an inter-laboratory study of the determination of acrylamide in crispbread and butter cookies have shown that only 50% of the participating laboratories reported satisfactory analytical values (Wenzl et al. 2004). Many of these methods do not perform well in difficult matrixes such as cocoa and coffee. As previously highlighted by some researchers, the selected mass transitions reveal difficulty of obtaining baseline separation in certain profiles during LCMS-MS analysis. The significant loss of the analyte throughout the sample preparation steps and ion suppression effect leading to a low response of acrylamide are common problems encountered after a two-step extract clean-up (Andrzejewski et al. 2004; Delatour et al. 2004). We previously described a sample preparation method for the determination of acrylamide in processed potato products using LC with diode array detection (Gökmen et al. 2005). Here, we also successfully applied same method for the determination of acrylamide in a variety of instant, ground and laboratory roasted coffees using LC-MS. The effects of temperature and time were also studied on the formation of acrylamide and colour in order to understand the changes and any relation in these variables during roasting process. Experimental procedures Chemicals and consumables Acrylamide (99þ%) and 13C3-labelled acrylamide (99% isotopic purity) were obtained from Sigma (Diesenhofen, Germany) and Cambridge Isotope Laboratories (Andover, MA, USA), respectively. Methanol, potassium hexacyanoferrate and zinc sulfate were analytical grade and obtained from Merck (Darmstadt, Germany). Bidistilled, deionized and 0.20 mm filtered water was used throughout the experiments. Oasis HLB (1 ml, 30 mg) SPE cartridges were supplied by Waters (Milford, MA, USA). Glass vials with septum screw caps and headspace vials seal caps were supplied by Agilent Technologies (Wilmington, DE, USA). Reference test material (FAPAS T3008 coffee) was obtained from CSL (Central Science Laboratory, UK) to verify the accuracy of method. Stock solution of acrylamide (1 mg/ml) and 13C3-labelled acrylamide (0.1 mg/ml) by dissolving in distilled water. Working standards were prepared daily by diluting the stock solution to concentrations of 0.01, 0.02, 0.05, 0.1, 0.2, 0.3, 0.5 and 1.0 mg/ml with distilled water. Carrez I solution was prepared by dissolving 15 g of potassium hexacyanoferrate in 100 ml of water, and Carrez II solution by dissolving 30 g of zinc sulfate in 100 ml of water. 215 Heat treatment (roasting) of green coffee A total of 3 g of ground green coffee was put in a headspace vial and sealed. Samples were roasted in a temperature-controlled oven (Heraeus Instruments model T 60) set to 150, 200 and 225 C for the determination of time-dependent changes in acrylamide and colour with sampling at 5, 10, 15, 20 and 30 min. Green coffee was spiked with 200 ng/g of deuterium labelled acrylamide in order to determine the rate of degradation at 225 C. Immediately after roasting for each selected time, the headspace vials were allowed to cool to room temperature prior to analyses. Measurement of acrylamide Sample preparation. A sample preparation procedure previously described by us elsewhere was used (Gökmen et al. 2005). A total of 1 g of coffee was weighed into a 10 ml centrifuge tube. The sample was spiked with acrylamide (50, 100, 250 and 500 ng/ g of acrylamide, and 50 and 100 n/g of 13C3-labelled acrylamide) to determine the percentage recovery of the method at this stage. The sample was suspended in 5 ml of methanol and extracted for 2 min in a vortex mixer. The suspension was centrifuged at 5000 rpm for 10 min (Sigma model 2–16 K). The clear supernatant was transferred into a centrifuge tube and treated with Carrez I and II solutions (25 ml each) to precipitate the co-extractives. Following centrifugation at 5000 rpm for 5 min, 1.0 ml of clear supernatant (0.2 g sample) was quantitatively transferred into a conical bottom glass test tube placed in a water bath at 40 C (Zymark Turbo VapÕ LV Evaporator) and evaporated to dryness under nitrogen at 3 psig. The remaining residue was immediately redissolved in 1 ml of water by mixing in a vortex mixer for 1 min. For the SPE clean-up, Oasis HLB cartridge was preconditioned consequently with 1 ml of methanol and 1 ml of water at a rate of two drops per second using a syringe. Then, 1 ml of the extract was passed through the cartridge at a rate of one drop per second using a syringe. The first ten drops of the effluent were discarded to prevent any dilution of sample by replacing water held in the sorbent void fraction with the sample effluent. The forthcoming drops were collected and filtered through a 0.45 mm syringe filter. 20 ml of the final test solution was injected onto LC column for quantitation by LC-APCI-MS. LC-APCI-MS analysis. LC-APCI-MS analyses were performed by an Agilent 1100 HPLC system (Waldbronn, Germany) consisting of a binary pump, an autosampler and a temperature-controlled column oven, coupled to an Agilent 1100 MS 216 H. Z. Şenyuva & V. Go¨kmen detector equipped with atmospheric pressure chemical ionization (APCI) interface. The analytical separation was performed on an Inertsil ODS-3 column (250 4.6 mm, 5 mm) using the isocratic mixture of 0.01 mM acetic acid in 0.2% aqueous solution of formic acid at a flow rate of 0.6 ml/min at 25 C. The LC eluent was directed to the MS system after a delay time of 6.5 min using MSD software. Data acquisition was performed in selected ion monitoring (SIM) mode using the interface parameters: Drying gas (N2, 100 psig) flow of 4 l/min, nebulizer pressure of 60 psig, drying gas temperatures 325 C, vaporizer temperature of 425 C, capillary voltage of 4 kV, corona current of 4 mA, fragmentor voltage of 55 eV. Ions monitored were m/z 72 and 55 for acrylamide and m/z 75 and 58 for 13C3-labelled acrylamide for the quantification of acrylamide in the samples. Measurement of CIE L*a*b* colour values Colour measurements (CIE L*a*b* values) were performed using a Minolta CM-3600d model spectrophotometer. According to CIE colour space, L* indicates lightness and a* and b* indicate color directions. þa* and a* are the red and the green directions, þb* and b* are the yellow and the blue directions, respectively. The sample was transferred into a disposable cuvette to measure the reflectance at least twice from both front and rear sides of the specimen. Results and discussion Performance of method for acrylamide Sample preparation. Since acrylamide is highly soluble in water (215.5 g/100 ml), the sample preparation was usually started by extracting the food samples with water enough for a proper swelling in most of the methods based on LC coupled to tandem MS detection system (Tareke et al. 2002; Rosén and Hellenäs 2002; Becalski et al. 2003; Roach et al. 2003; Riediker and Stadler 2003). Our initial attempts of analysing coffee samples for acrylamide which started with extraction with water resulted in undesirable results during LC-MS analyses due to interfering co-extractives. These interfering co-extractives could not be eliminated completely after a single SPE clean-up in different modes including hydrophilic-lipophilic balanced copolymer sorbent packed cartridge (Oasis HLB) and cationanion exchanger based sorbent packed cartridges (Oasis MCX or MAX), and satisfactory chromatograms could not be obtained. In fact, peaks of acrylamide and interferences completely overlapped each other and co-detected during MS detection in SIM mode. Co-detection of acrylamide and interferences in coffee extract was confirmed by analysing the purity of co-eluted peaks in scan mode. The ion having m/z of 71 appeared as the major interference during the MS detection of acrylamide in SIM mode. Some researchers, therefore, used sequential SPE cartridge clean-up using Oasis HLB cartridge and then a Bond Elut-Accucat (cation and anion exchange sorbent) cartridge. However, a number of peaks were observed both before and after the acrylamide peak in the ion profiles monitored for coffee extracts during LCMS-MS analysis, despite two SPE cartridge clean-up steps (Andrzejewski et al. 2004). The significant loss of the analyte and ion suppression effect leading to a low response of acrylamide were also encountered after a two-step extract clean-up approach with Isolute Multimode and cation-exchange cartridges for coffee (Delatour et al. 2004). Recently, a singlestep clean-up procedure using Isolute multimode solid phase cartridge was described for the analysis of acrylamide in ready-to-drink coffee. However, it was noted that the loading of the SPE cartridge with the sample exceeding 0.5 ml resulted in an increased suppression of the MS response (Granby and Fagt 2004). Acrylamide is also highly soluble in methanol (155.0 g/100 ml) which can be used as an alternative extracting solvent. It was previously shown by us elsewhere that methanol as the extraction solvent was successfully applied for the analysis of acrylamide in potato chips and crisps with subsequent Carrez clarification and SPE cleanup (Gökmen et al. 2005). Here, the same approach was applied for the analysis of acrylamide in coffee. After acrylamide was extracted from coffee with methanol, the colloids (mainly proteins) which were soluble in methanol were precipitated by Carrez reagents. Carrez clarification not only purified the extract by precipitation of dissolved colloids, but also prevented the loss of acrylamide during the evaporation of methanol under a gentle stream of nitrogen. The addition of 50 ml of water added into approximately 5 ml of methanolic extract in the form of aqueous Carrez I and II solutions had a significant contribution to retain acrylamide residue on the wall of glass tube during evaporation. Following evaporation to complete dryness, the residue on the wall of glass tube was redissolved by water in a vortex mixer. By changing solvent from methanol to water, lipophilic co-extractives present in the methanolic extract of coffee were excluded leaving them as a residue on the wall of glass tube, but acrylamide was completely transferred into water. The extract was further cleaned up by using Oasis HLB cartridge. Since acrylamide does not interact with the sorbent material, the pass through strategy during the SPE Study of acrylamide in coffee Table I. Percentage recoveries of acrylamide from ground filter coffee for different spiking levels. abundance interference 1200 Spiking level, ng/g 50 100 250 500 Recovery, % 217 RSD, % (n ¼ 4) AA d3-AA AA d3-AA 98.8 100.0 100.0 101.5 100.5 101.2 – – 0.5 1.0 0.6 1.0 1.1 0.9 1.0 1.5 1100 1000 acrylamide 900 800 clean-up was applied to retain only the matrix interferences. It was determined that first ten drops (0.4 ml) should be discarded, then collecting the remaining effluents (0.6 ml) during SPE clean-up to prevent any dilution with water left in the cartridge after conditioning. Doing so, a colourless final extract could be obtained prior to LC-MS analyses for coffee samples, excepting instant coffees. The recovery of acrylamide was determined by analysing each of the spiked sample four times for levels ranging from 50–500 ng/g. Recovery samples were prepared by spiking ground filter coffee containing an acrylamide level of 49.0 1.0 ng/g. The mean percentage recoveries exceeded 99% for all spiking levels for coffee (see Table I). The accuracy of the method was further tested analysing reference material (FAPAS T3008 coffee) supplied by the CSL. The mean value of acrylamide was found to be in the satisfactory range. 700 600 6.5 6 7 7.5 min Figure 1. Chromatogram of coffee showing the co-elution of acrylamide and interfering co-extractive in the presence of acetonitrile in the mobile phase mixture. abundance spiked coffee (+50 ng/g acrylamide) 800 750 blank coffee (~50 ng/g acrylamide) 700 10 ng/ml acrylamide standard 650 600 Chromatographic separation The chromatographic separation of acrylamide was performed on an Inertsil ODS-3 analytical column. Initially, the isocratic mixture of 0.01 mM acetic acid in 0.2% aqueous solution of formic acid and 0.2% acetic acid in acetonitrile (98:2, v/v) as the mobile phase at a flow rate of 0.6 ml/min was used to separate acrylamide from the matrix co-extractives of coffee samples. As reported by us elsewhere, acrylamide could be successfully resolved from the matrix co-extractives using these chromatographic conditions during the analysis of acrylamide in potato and cereal based foods using LC-MS with APCI (Şenyuva and Gökmen 2005). However, co-eluting compounds from the coffee extract interfered with acrylamide during MS detection in SIM mode as illustrated in Figure 1. In order to improve chromatographic separation, acetonitrile was excluded from the mobile phase mixture. Doing so, acrylamide and interfering co-extractive was completely resolved using the isocratic mixture of 0.01 mM acetic acid in 0.2% aqueous solution of formic acid at a flow rate of 0.6 ml/min (Figure 2). 550 8.5 9.0 min Figure 2. Chromatograms of coffee blank, coffee spiked with 50 ng/g of acrylamide, and acrylamide standard 10 ng/ml. Detection sensitivity and linearity LC-MS with APCI allowed us to determine acrylamide sensitively and precisely. Under the positive APCI conditions applied here, scan MS analysis of acrylamide and 13C3-labelled acrylamide showed both [MþH]þ ions with compoundspecific product ions due to loss of NH3 from the protonated molecule. The acrylamide response was linear over a concentration range of 1–1000 ng/ml with correlation coefficients of higher than 0.999. Based on a signal to noise ratio of 3, limit of detection (LOD) and limit of quantitation (LOQ) was found to be ca. 2.0 ng/g and 10.0 ng/g acrylamide in coffee. H. Z. Şenyuva & V. Go¨kmen 350 Table II. Acrylamide level of commercial coffee samples. 300 29–75 50 42–338 250 150 100 0 0 5 10 15 20 25 30 time, min Figure 3. Acrylamide formation during roasting of green coffee at different temperatures. 350 7 (a) acrylamide, ng/g 300 250 6 5 Acrylamide Color 200 4 150 3 100 2 50 1 0 0 0 5 10 15 20 25 30 time, min 350 7 (b) acrylamide, ng/g 300 6 Acrylamide 250 5 Color 200 4 150 3 100 2 50 1 0 Effect of heat treatment (roasting) on acrylamide and colour 0 0 5 10 15 20 25 30 time, min 7 350 (c) 300 acrylamide, ng/g In order to determine the effects of heating on the amounts of acrylamide in relation to colour, green coffee was roasted at three temperatures of 150, 200 and 225 C for up to 30 min. The amount of acrylamide measured increased rapidly at the onset of roasting, reaching an apparent maximum, and then decreasing exponentially as the rate of degradation exceeded the rate of formation at 200 and 225 C. However, the amount of acrylamide measured continued to increase during roasting at 150 C. As illustrated in Figure 3, experiments with deuterium labelled acrylamide spiked to green coffee prior to roasting confirmed the exponential degradation during heating at 225 C. The acrylamide level 200 50 Survey of acrylamide in commercial coffee samples In this study, a total of 20 coffee samples from four groups were analysed for their acrylamide contents. Samples were randomly selected from coffee shops and supermarkets in Ankara in December 2004, therefore, may not representative of coffee supply. We would like to stress that results cannot provide guidance in consumers’ choice between different products and brands within certain Turkish coffee types. However, the results are a general guide to acrylamide concentrations in a selected segment of coffee supply. According to our results, acrylamide levels averaged as 19 ng/g in roasted ground coffees from different origins. The acrylamide levels of Turkish type coffee was slightly higher and averaged as 46 ng/g. Gold type instant coffees were found to contain significantly higher amounts of acrylamide (see Table II). Andrzejewski et al (2004) have reported the average acrylamide levels ranging from 45 ng/g to 374 ng/g in 31 ground coffees. 225 deg C 225 deg C (d3-acrylamide) CIE a* value 14 18 29 15 22 15 18 12 28 21 18 200 deg C CIE a* value Turkish coffees (n ¼ 5) Filter coffee (n ¼ 1) Instant coffees (n ¼ 3) Roasted ground coffees (n ¼ 11) Irish coffee Mexico Costa Rica S.H.B. Tanzanian peaberry Colombian supremo Colombian decaffeinated Guatemala Yemen mocha Indonesian sumatra Ethiopian mocha Kenya 150 deg C Acrylamide, ng/g acrylamide,ng/g Coffee sample 6 Acrylamide 250 5 Color 200 4 150 3 100 2 50 1 CIE a* value 218 0 0 0 5 10 15 time, min 20 25 30 Figure 4. Changes in the amount of acrylamide and CIE a* value in coffee during heating at (a) 150 C, (b) 200 C, (c) 225 C. Study of acrylamide in coffee was reduced by a factor of approximately 20 at the end of 30 min of roasting at 200 and 225 C, compared to the highest level recorded. As noted by other researchers (Taeymans et al. 2004), the results obtained in this study also revealed that the darker coloured coffee may contain much lower amounts of acrylamide than light coloured coffee. Changes in the CIE L*a*b* colour values of coffee were also monitored during roasting. Although CIE L* and b* values decreased exponentially with time, CIE a* values measured increased rapidly at the onset of roasting, reaching an apparent maximum, and then decreasing exponentially at 200 and 225 C, but reached to a maximum with continuous increase at 150 C. It was interesting to see that changes in the amounts of acrylamide and CIE a* values followed almost the same pattern, as shown in Figure 4. These results recommend that there is a significant correlation between the amount of acrylamide and the CIE a* value of roasted coffee. Since similar correlations were obtained between the amount of acrylamide and CIE a* value during roasting at all temperatures studied, it was concluded that the 7 6 CIE a* value 5 4 y = 1.4364Ln(x) - 2.3366 3 2 r = 0.9286 2 1 0 0 50 100 150 200 250 300 350 acrylamide, ng/g Figure 5. Non-linear function for the correlation between acrylamide concentration and CIE a* value for roasted coffee. correlation between acrylamide and CIE a* value is independent of temperature. Therefore, the acrylamide level of coffee can be estimated roughly from the measured CIE a* value by knowing a reasonable regression equation. Here, randomly selected data points (measured acrylamide concentrations versus CIE a* values) for roasted green coffee were used to perform non-linear regression analysis. A logarithmic function was fitted well to the experimental data as shown in Figure 5. Acrylamide concentrations of a variety of roasted coffee samples were determined roughly using this function. As seen in Table III, the difference between the predicted and measured acrylamide concentrations was ranged from 1–59% for roasted coffees of different origin, as well as for a commercial gold type instant coffee. Conclusions Coffee was studied in a time-dependent manner to determine the effects of roasting temperature in the amounts of acrylamide in relation with colour. A significant correlation was found between the acrylamide level and colour measured as CIE a* value. This correlation was fitted to a non-linear logarithmic function and successfully used to predict acrylamide concentration from the measured CIE a* value in a variety of commercial coffee samples. The preliminary results show that the acrylamide level in roasted coffee may be estimated approximately from the CIE a* value. However, further investigation is required to establish a more useful relation based on a statistical database for roasted coffees taking the variations in raw material origin into account for an accurate prediction of acrylamide levels in roasted coffee. The method used to analyse acrylamide in coffee was rapid, rugged and accurate, utilizing methanol extraction and clean-up steps prior to LC-MS analysis. Since the sample preparation method presented here can be applied to basically all foods Table III. Measured and predicted AA levels of ground roasted coffee samples using the logarithmic correlation model. Measured Roasted coffee Mexico Irish coffee Tanzanian peaberry Colombian supremo Guatemala Colombian decaf Indonesian sumatra Ethiopian mocha Jacobs monarch 219 Predicted Acrylamide, ng/g CIE a* colour Acrylamide, ng/g Difference, % 18 14 15 22 18 15 28 21 338 2.22 2.20 2.17 2.11 2.30 2.14 2.59 2.48 5.94 24 22 23 22 25 22 31 29 318 33 59 54 1 40 50 10 36 6 220 H. Z. Şenyuva & V. 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