A Vietnam Robusta grade 2 and an unwashed Brazil Arabica were used as the starting material. Different production areas and treatments can give rise to a variation of coffee constituents and consequently also the formation of food born toxicants. This was not the subject of our study. For some experiments a Kenya Arabica speciality coffee was analyzed. The coffees were roasted on a smaller scale (1 kg and 4 kg) in two different industry plants using drum and tangential roasting or hot air roasting devices. Tangential roasts were used for short roasting times as the drum roaster was not capable to work with shorter roasting times.
This approach was to ensure the possibility of a scale-up because using roasting on the lab scale will not allow this. To understand the influence of decaffeination, the samples were also decaffeinated using dichloromethane and some samples with water in an industrial plant. Another treatment analyzed was steam treatment, which is also carried out industrially. The following parameters were employed:
The coffees were roasted according to three different profiles. Briefly, profile 1 includes a linear temperature increase, while roasting profile 2 the temperature is higher in the early phase of roast. Profile 3 is characterized by a small increase of the temperature in the beginning and a fast increase at the end. Figure 3 shows the different profiles.
The roasting profiles of the first series[].
The coffees were roasted to a light, medium and dark roast by varying the roasting time (5, 10, 15 and 20 min) within the individual profiles. The roasts were characterized by evaluating the color by measuring the light reflectance on two different devices (see below). Overall in the first roasting series, 72 samples of Brazil Arabica and 71 Vietnam Robusta samples were produced from each green coffee.
The coffees were roasted on day 1 until 150 °C according to the corresponding roasting profile and completely cooled down (ambient air). On the next day the samples were roasted to the final degree of roast according to the profiles.
Roasting with sudden temperature change
Within the capabilities of the roasters a more rapid rise of the temperature compared to the normal profiles was employed.
Both coffees were decaffeinated in an industrial plant using dichloromethane and roasted according to all three profiles. For the Robusta samples, a water decaffeination was also employed in an industrial plant .
Steam treatments are used to remove coffee wax. This treatment is believed to improve the tolerability of coffee even in sensitive subjects. The steam treatment was also carried out under typical industrial conditions (NKG Kala, Hamburg, Germany).
Color measurements of ground coffee to determine the degree of roast
The ground samples were characterized using a Colorette 4 (reflected light is measured). Data are given as Colorette scale units (0–200 / 0 = dark; 200 = light), also the L* a* b*- color data have been recorded. For some samples, the roasting loss/organic roasting loss was determined gravimetrically.
The solvents were of HPLC or MS grade, gases and all reagents used were of analytical grade. Acrylamide was obtained from VWR Int. S.A.S. (Darmstadt, Germany). Acrylamide-d3, sodium tetraborate decahydrate, sodium thiosulfate pentahydrate, triethylamine, hydrobromic acid, furan (99%), furan-d4 (≥ 99.9%), 2-methylfuran (99.1%), 3-methylfuran (99.1%), 2,5-dimethylfuran (99%) were supplied by Sigma Aldrich (Steinheim, Germany). 2,5-dimethylfuran-d3 (≥ 95%), 2-methylfuran-d3 (≥ 95%) and 3-methylfuran-d3 (≥ 95%) were supplied by Toronto Research Chemicals (Toronto, Canada). Bromine and methanol were purchased from Merck KGaA (Darmstadt, Germany). Other chemicals came from Carl Roth (Karlsruhe, Germany).
Sample preparation for acrylamide determination
The coffee samples were stored at –18 °C to avoid losses of acrylamide, furan and methylfurans as initial experiments had shown a degradation of acrylamide during storage at ambient temperature (see also below). DIN EN ISO 18862 was used for the quantification of acrylamide by GC-MS/MS after derivatization. Briefly, the coffee beans were ground in a mill with nitrogen cooling. To the homogenized sample (2 g) 100 µL acrylamid-d3 standard solution (c = 10 µg/L), 2 ml n-hexane and 20 ml deionized water was added to a 50 ml centrifuge tube and extracted in an ultrasonic bath at 40 °C for 15 min. After that, the tube was centrifuged (4,000 rpm). Ten ml of the aqueous phase was taken in a 15 ml centrifuge tube, and 1 ml carrez I and 1 ml carrez II solution were added, followed by mixing and centrifugation at 4,000 rpm for 4 min. The supernatant was purified by SPE (using a Chromabond ABC18 SPE, Machery-Nagel, Düren, Germany). The residue was washed with 3 ml deionized water, centrifuged and again purified by SPE. For quantification an external calibration plot was used with stable isotope dilution analysis (SIDA). Concentrations were 0.0025–0.1 µg/L.
Sample preparation for the determination of furan and methylfurans
The method is based on a German standard method for furan and a thesis on the determination of methylfurans. Briefly, the samples were ground in a mill with nitrogen cooling and 1 g of the homogenized sample was added to a 20 ml headspace vial (baked out before use) and overlaid with 9 ml of water. Under the surface, 40 µl of the deuterated standards solution was added using a syringe. After that the headspace vial was sealed with a gastight cap and measured by HS-GC-MS. The concentrations used were as follows:
Furan 50–2,000 µg/L; furan-d4 400 µg/L; 2-methylfuran 100–4,000 µg/L, 2-methylfuran-d3 500 µg/L; 3-methylfuran 10–400 µg/L, 3-methylfuran-d3 80 µg/L; 2,5-dimethylfuran 10–400 µg/L, 2,5-dimethylfuran 80 µg/L.
GC-MS: (used for both acrylamide and furans determination) (Table 1) :
Table 1. GC-MS settings for both acrylamide and furans determination.
GC Trace 1300 GC (Thermo Fisher Scientific, Dreieich, Germany) PTV mode CT split Inlet temperature 240 °C Column VF-WAXms, 30 m, ID 0.25 mm, 0.25 μm (Agilent J & W Columns, Waldbronn, Germany) Carrier Helium 5.0 Mass spectrometer TSQ DUO (Thermo Fisher Scientific, Dreieich, Germany) Data processing Thermo TraceFinder GC 3.2, Thermo Xcalibur 3.0 (Thermo Fisher Scientific, Dreieich, Germany) Ionisation mode EI+, 70 eV MS transfer line/ion source temperature 250 °C Collision gas Argon Mode SRM (acrylamide) and SIM (furans) Autosampler Acrylamide: TRIPLUS RSH with 10 μl Syringe,
57 mm (Thermo Fisher Scientific, Dreieich, Germany) Furans: TRIPLUS RSH, Temperature
70 °C, with 5 mL syringe, 65 mm; (Thermo Fisher Scientific, Dreieich, Germany)
Split flow 12.0 ml/min (acrylamide) and splitless (furans) Flow 1.2 ml/min (acrylamide) and 1.0 mL/min (furans) Carrier mode Constant flow
Table 2. Ions used for the identification and quantification of acrylamide.
2-Bromopropenamide Identification + quantification: m/z 149 [C3H479BrON]+→ 106 [C2H379Br]+ (identification) D2-Bromopropenamide Identification and quantification: m/z 153 [C32H21H381BrON]+→ 110 [C22H21H181Br]+ (identification)
Table 3. Ions used for the identification and quantification of furans.
Analyte Ions [m/z] Furan 68 [C4H4O]+ (identification and quantification) 2-methylfuran/3-methylfuran 82 [C5H6O]+ (identification and quantification) 81 (identification) 2,5-dimethylfuran 95 [C6H7O]+ (identification and quantification) 96 (identification) D4-furan 72 [C4D4O]+ (identification and quantification) D3-2-methylfuran/D3-3-methylfuran 85 [C5H3D3O]+ (identification and quantification)84 (identification) D3-2,5-dimethylfuran 98 [C6H4D3O]+ (identification and quantification)99 (identification)
Principal Component Analysis was used to evaluate the possible correlations between the concentrations of process contaminants and roasting parameters. The results are not presented in detail here but can be withdrawn from Bahar and Delker[24, 25].
All samples were evaluated by a sensory panel (in-house, 10 panelists) to check whether or not the samples are within consumer's expectation. As there were no deviations the results are not given here[24, 25].
It can be finally concluded that Arabica and Robusta samples behaved similar to each other. The acrylamide content was negligible in green coffee and increased rapidly in the early stage with a maximum in light roast. After that, the acrylamide content decreased with increasing degree of roast. Furan and methylfurans content increased during roasting and was highest in dark roasted coffees.
It can be concluded that mitigation options are available for acrylamide or furan/methylfurans, however, a simultaneous mitigation seems to not be possible. This has to be taken in account if limits or guiding values are be set in the future.
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Engelhardt UH, Bahar I, Delker U. 2023. Food borne toxicants in coffee: Acrylamide and furan derivative content in Arabica and Robusta coffees with different roasting profiles and varying degrees of roast. Beverage Plant Research 3:8 doi: 10.48130/BPR-2023-0008
Food borne toxicants in coffee: Acrylamide and furan derivative content in Arabica and Robusta coffees with different roasting profiles and varying degrees of roast
- Received Date: 08 January 2023
- Revised Date: 05 February 2023
- Accepted Date: 09 February 2023
- Published Online: 03 April 2023