Determination of toxic α-dicarbonyl compounds in sesame oils using dispersive liquid-liquid microextraction coupled with gas chromatography-mass spectrometry

Abstract

Glyoxal, methylglyoxal, and diacetyl are toxic α-dicarbonyl compounds found in heat-processed foods, including edible oils. Dispersive liquid-liquid microextraction was combined with gas chromatography mass spectrometry to determine the glyoxal, methylglyoxal, and diacetyl contents in sesame oil. Chloroform and methanol were selected as the optimal extraction and dispersive solvents, respectively. The maximum derivatization efficiency was obtained using 500 µg of the derivatization agent, o-phenylenediamine. The derivatization of glyoxal was completed in 1 h, whereas those of methylglyoxal and diacetyl were completed immediately. The optimized method was validated, and was found to exhibit a good linearity, recovery, intraday repeatability, and interday reproducibility. The α-dicarbonyl compound concentrations in the oils were dependent on the roasting temperature. The sesame oil concentrates contained 0-175.4, 0-990.5, and 0-220.9 ng g^-1 of glyoxal, methylglyoxal, and diacetyl, respectively. For the perilla oils, the respective concentrations were 0-96.4, 0-410.8, and 0-197.5 ng g^-1.

Keywords: Diacetyl; Dispersive liquid–liquid microextraction; Glyoxal; Methylglyoxal; Sesame oil.

Fig. 1

Optimization of the extraction and derivatization conditions. (A, B) Optimization of the extraction and dispersive solvents. (A) Selection of the extraction solvent (aqueous phase vol. = 3 mL; compound concentration = 250 ng mL⁻¹; o-phenylenediamine dihydrochloride (oPD) = 0.5 mg; derivatization time = 2 h; dispersive solvent = methanol; dispersive solvent vol. = 0.2 mL; buffer = 0.5 M sodium phosphate buffer at pH 7.6). (B) Selection of the dispersive solvent (aqueous phase vol. = 3 mL; compound concentration = 250 ng mL⁻¹; oPD = 0.5 mg; derivatization time = 2 h; extraction solvent = chloroform; extraction solvent volume = 100 µL; buffer = 0.5 M sodium phosphate buffer at pH 7.6). Data are shown as the mean ± standard deviation (n = 3). (C, D) Optimization of the extraction and dispersive solvent volumes. (C) Optimization of the extraction solvent volume (extraction conditions: aqueous phase vol. = 3 mL; compound concentration = 250 ng mL⁻¹; oPD = 0.5 mg; derivatization time = 2 h; dispersive solvent = methanol; dispersive solvent vol. = 0.2 mL; extraction solvent = chloroform; buffer = 0.5 M sodium phosphate buffer at pH 7.6). (D) Optimization of the dispersive solvent volume (extraction conditions: aqueous phase vol. = 3 mL; compound concentration = 250 ng mL⁻¹; oPD = 0.5 mg; derivatization time = 2 h; dispersive solvent = methanol; extraction solvent = chloroform; extraction solvent vol. = 100 µL; buffer = 0.5 M sodium phosphate buffer at pH 7.6). Data are shown as the mean ± standard deviation (n = 3). (E, F) Optimization of the derivatization parameters. (E) Optimization of the amount of derivatizing agent (aqueous phase = 3 mL; compound concentration = 250 ng mL⁻¹; oPD = 0.5 mg; derivatization time = 2 h; extraction solvent = chloroform; extraction solvent volume = 100 µL; buffer = 0.5 M sodium phosphate buffer at pH 7.6). (F) Optimization of the derivatization time. Data are shown as the mean ± standard deviation (n = 3). Q, quinoxaline; 2-MQ, 2-methylquinoxaline; 2,3-DMQ, 2,3-dimethylquinoxaline.

Fig. 2

Representative chromatograms obtained in the selected ion monitoring (SIM) mode. (A) SIM chromatogram of the standard glyoxal, methylglyoxal, and diacetyl solutions (20 ng mL⁻¹ in each case). (B) SIM chromatogram of the sample (sesame oil No. 1). Q, quinoxaline; 2-MQ, 2-methylquinoxaline; 2,3-DMQ, 2,3-dimethylquinoxaline; 1-MP, 1-methylpyrazine (internal standard, ISTD). (C) Mass spectra of Q, 2-MQ, and 2,3-DMQ in the sample (sesame oil No.1) obtained in the SIM mode.

Fig. 3

Effects of the roasting temperature and time on the generation of α-dicarbonyl compounds in the oils of sesame and perilla seeds. (A) Effect of the roasting temperature and time on the α-dicarbonyl compound contents in the sesame oil. (B) Effect of the roasting temperature and time on the α-dicarbonyl compound contents in the perilla oils. Data are shown as the mean ± standard deviation (n = 3).