Gas Chromatography–Mass Spectrometry Analysis of 4-Methylimidazole in Balsamic Vinegars and Processed Sauces

Multivariate optimization for extraction of 2-methylimidazole and 4-methylimidazole from açaí-based food products using polymeric ionic liquid-based sorbent coatings in solid-phase microextraction coupled to gas chromatography-mass spectrometry

In this study, polymeric ionic liquids featuring different functional moieties were applied as sorbent coatings in direct-immersion solid-phase microextraction (DI-SPME) for the extraction of 2-methylimidazole (2-MI) and 4-methylimidazole (4-MI) from açaí-based food products followed by gas chromatography-mass spectrometry (GC-MS) analysis. The analytical method was optimized using a sequential experimental design. Variables used in GC-MS such as desorption time, as well as for SPME-DI, including extraction time, extraction temperature, incubation time of extraction, amount of NaCl in the extract, and stirring rate, were optimized. The fitness-for-purpose of the method was verified by the linearity of matrix-matched calibration curves (R2 ≥ 0.9921), adequate recoveries (81.7-89.7 %), and precision (relative standard deviations ≤11.2 %). The method was applied to twenty-five samples of açaí-based food products. 4-MI was found in four samples whereas 2-MI was not detected above the limit of detection. The method was found to be suitable for quality control analysis.

4-Methylimidazole, a carcinogenic component in food, amount, methods used for measurement; a systematic review

4-methylimidazole (4-MEI) is widely used industrially. This carcinogenic component has been reported in some types of food. It is usually produced by the caramelization process in food, drinks and caramel coloring. The possible mechanism for the formation of this compound in food is the Maillard reaction. In order to estimate the amount of substance 4-MEI in food, a systematic study was conducted. The selected keywords were 4-methylimidazole, 4-MEI, beverage, drink, meat, milk, and coffee. 144 articles were obtained from the initial search. The articles were evaluated and finally, the data of 15 manuscripts were extracted. Based on the data extracted from selected articles, the highest amount is reported in caramel color, coffee, and cola drinks. In 70% of the selected studies, the analytical method was based on liquid chromatography. In this method, there is no need for derivatization. SPE columns were used to extract samples in most manuscripts. According to per capita consumption, the most exposure to 4-MEI is through coffee. In high risk food products, regular monitoring with analytical methods with high sensitivity is recommended. Furthermore, most of the selected studies were about the validation method, so few samples were selected. It is recommended to design more studies with a high sample size to accurately evaluate this carcinogenic compound in food.

Application of gas flow headspace liquid phase micro extraction coupled with gas chromatography-mass spectrometry for determination of 4-methylimidazole in food samples employing experimental design optimization

Background

4-Methylimidazole (4-MeI) or 4-methyl-1H-imidazole, a slightly yellowish solid with molecular formula C₄H₆N₂, is a heterocyclic compound which supposedly does not exist as a natural product and is formed when carbohydrates are heating with ammonium compounds. This compound is used in pharmaceuticals, agriculture and photography chemicals, dyes and pigments, and rubber manufacturing. In the present study, a simple and efficient sample preparation method designated gas flow headspace liquid phase microextraction (GF-HS-SDME) was employed for the extraction and preconcentration of 4-methylimidazole (4-MeI) from food and beverage samples, before its determination by gas chromatography-mass spectrometry.

Result

To investigate the optimal conditions for the extraction process in GF-HS-SDME method, factors affecting extraction, including selection of extraction solvent, vial volume, extraction solvent ratio, position of extracting solvent, drop volume, sample volume, stirring speed, temperature, extraction time, sample pH, ionic strength of the sample solution and gas flow rate were optimized by utilizing both one-variable-at-a-time method and Plackett–Burman design. The investigation of protocol was carried out by using a standard solution containing 100.0 μg L⁻¹ of 4-MeI in deionized water.

Conclusion

In this study, a simple and green analytical method based on GF-HS-SDME was proposed for the extraction and preconcentration of 4-MeI from foodstuffs, followed by GC–MS determination. The main advantage of this method is its high preconcentration factor and fastness due to the application of an inert gas stream during microextraction.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13065-022-00823-z.

A Review of the Analytical Methods for the Determination of 4(5)-Methylimidazole in Food Matrices

4(5)-Methylimidazole (4(5)MEI) is a product of the Maillard reaction between sugars and amino acids, which occurs during the thermal processing of foods. This compound is also found in foods with caramel colorants additives. Due to its prevalence in foods and beverages and its potent carcinogenicity, 4(5)MEI has received federal and state regulatory agency attention. The aim of this review is to present the extraction procedures of 4(5)MEI from food matrices and the analytical methods for its determination. Liquid and gas chromatography coupled with mass spectrometry are the techniques most commonly employed to detect 4(5)MEI in food matrices. However, the analysis of 4(5)MEI is challenging due to the high polarity, water solubility, and the absence of chromophores. To overcome this, specialized sample pretreatment and extraction methods have been developed, such as solid-phase extraction and derivatization procedures, increasing the cost and the preparation time of samples. Other analytical methods for the determination of 4(5)MEI, include capillary electrophoresis, paper spray mass spectrometry, micellar electrokinetic chromatography, high-performance cation exchange chromatography, fluorescence-based immunochromatographic assay, and a fluorescent probe.

Dispersive liquid-liquid microextraction with in situ derivatization coupled with gas chromatography and mass spectrometry for the determination of 4-methylimidazole in red ginseng products containing caramel colors

A rapid analytical method was developed for the determination of 4-methylimidazole from red ginseng products containing caramel colors by using dispersive liquid-liquid microextraction with in situ derivatization followed by gas chromatography with mass spectrometry. Chloroform and acetonitrile were selected as the extraction and dispersive solvents, and based on the extraction efficiency, their optimum volumes were 200 and 100 μL, respectively. The optimum volumes of the derivatizing agent (isobutyl chloroformate) and catalyst (pyridine), pH, and concentration of NaCl in the sample solution were determined to be 25 and 100 μL, pH 7.6, and 0% w/v, respectively. Validation of the optimized method showed good linearity (R²  > 0.999), accuracy (≥89.86%), intra- (≤6.70%) and interday (≤4.17%) repeatability, limit of detection (0.96 μg/L), and limit of quantification (5.79 μg/L). The validated method was applied to quantify 4-methylimidazole in red ginseng juices and concentrates, 4-methylimidazole was only found in red ginseng juices containing caramel colorant (42.91-2863.4 μg/L) and detected in red ginseng concentrates containing >1% caramel colorant.

Determination of 4-Methylimidazole in Ammonia Caramel Using Gas Chromatography–Tandem Mass Spectrometry (GC-MS/MS)

One of Maillard reaction products formed in the production of ammonia caramel is 4(5)-methylimidazole (4-MeI) classified as carcinogen. A method of 4-MeI determination based on ion-pair extraction and derivatisation with isobutyl chloroformate with subsequent gas chromatography-tandem mass spectrometry analysis was proposed. Tandem mass spectrometry was applied to reduce the influence of matrix and increase the selectivity and sensitivity of the method. Triple quadrupole GC-MS system was used for this study. The collision energies were optimized for MRM mode. The detection (LOD) and quantification limits (LOQ) of the elaborated method were 17 and 37.8 μg kg−1, respectively, repeatability was <15% RSD for analyzed caramel samples, and the recovery for 4-MeI was 101%. Comparison of MS/MS with SIM detection on the same instrument proved almost 30 times lower LODs achieved by tandem mass spectrometry compared to SIM. Described method can be routinely used for monitoring 4-MeI as a quality and safety marker in the production of ammonia caramel.

Reduction of 4(5)-Methylimidazole Using Cookie Model Systems

The objective of this study was to determine the reduction of 4(5)-methylimidazole (4-MI) under various baking conditions. For 4-MI analysis, an analytical method using gas chromatography-mass spectrometry was developed. The developed method was validated with linearity (r² > 0.999), recovery (101% to 103%, 3 levels), and precision (1.5% to 4.3%, 3 levels). Limits of detection and quantification were 18.5 and 56.0 μg/kg, respectively. This method was used to monitor the level of 4-MI in 11 commercial cookies, which ranged from 71.5 to 1254.8 μg/kg. Time and temperature were modified in the cookie model system to reduce 4-MI. The largest reduction in 4-MI (56%) was achieved by baking at 140 °C for 8 min; however the cookies baked at this condition were not well accepted by consumers. With combination of consumer liking test result, baking cookies at 140 °C for 16 min is optimal for 4-MI reduction (28% reduction), while it has minimal impact on consumer acceptance. A strong correlation (r² = 0.9981) was found between caramel colorant and 4-MI in the cookie model system.

PRACTICAL APPLICATION

A consumer awareness toward toxicity of 4-MI has been arising, and method to reduce the levels of 4-MI in food products are being developed in many studies. Yet, these reduction studies in food model systems only focused on use of food additives for 4-MI reduction. Current study investigated the use of process modification on 4-MI reduction in cookie, and suggested that baking cookies longer at lower temperature, in turn, reduces the levels of 4-MI in cookies without compromising consumer acceptance. Finding from current study can practically aid bakery industry to ensure safety of bakery products without affecting consumer likings.