SIMULTANEOUS DETECTION OF ETHYL CARBAMATE AND UREA IN CHINESE YELLOW RICE WINE BY HPLC-FLD

Occurrence of Ethyl Carbamate in Foods and Beverages: Review of the Formation Mechanisms, Advances in Analytical Methods, and Mitigation Strategies

ABSTRACT

Ethyl carbamate (EC) is a process contaminant that can be formed as a by-product during fermentation and processing of foods and beverages. Elevated EC concentrations are primarily associated with distilled spirits, but this compound has also been found at lower concentrations in foods and beverages, including breads, soy sauce, and wine. Evidence from animal studies suggests that EC is a probable human carcinogen. Consequently, several governmental institutions have established allowable limits for EC in the food supply. This review includes EC formation mechanisms, occurrence of EC in the food supply, and EC dietary exposure assessments. Current analytical methods used to detect EC will be covered, in addition to emerging technologies, such as nanosensors and surface-enhanced Raman spectroscopy. Various mitigation methods have been used to maintain EC concentrations below allowable limits, including distillation, enzymatic treatments, and genetic engineering of yeast. More research in this field is needed to refine mitigation strategies and develop methods to rapidly detect EC in the food supply.

HIGHLIGHTS

Biodegradation of Ethyl Carbamate and Urea with Lysinibacillus sphaericus MT33 in Chinese Liquor Fermentation

It is important to reduce the concentration of ethyl carbamate (EC) in fermented foods. However, controlling the formation of EC and its precursor urea is difficult in spontaneous food fermentation because urea is a natural product of nitrogen metabolism. Biodegradation is a better solution to reduce the concentration of EC. This study aimed to reduce the concentration of EC in Chinese liquor via an indigenous strain Lysinibacillus sphaericus MT33. This strain produced urethanase (940 U/L) and urease (1580 U/L) and degraded 76.52% of EC and 56.48% of urea. After inoculation in liquor fermentation, the maximal relative abundance of Lysinibacillus increased from 0.02% to 8.46%, the final EC and urea contents decreased by 41.77% and 28.15%. Moreover, the concentration of EC decreased by 63.32% in liquor. The negative correlation between abundance of Lysinibacillus and contents of EC and urea indicated the effect of L. sphaericus on EC and urea degradation.

Urea production by yeasts other than Saccharomyces in food fermentation

Urea is an important intermediate in the synthesis of carcinogenic ethyl carbamate in various food fermentations. Identifying urea-producing microorganisms can help control or reduce ethyl carbamate production. Using Chinese liquor fermentation as a model system, we identified the yeasts responsible for urea production. Urea production was positively correlated to the yeast population (R = 0.523, P = 0.045), and using high-throughput sequencing, we identified 26 yeast species. Partial least squares regression and correlation analysis indicated that Wickerhamomyces anomalus was the most important yeast to produce urea (variable importance plot = 1.927; R = 0.719, P = 0.002). Besides, we found that in W. anomalus the CAR1 gene (responsible for urea production) was 67% identical to that of Saccharomyces cerevisiae. Wickerhamomyces anomalus produced more urea (910.0 μg L-1) than S. cerevisiae (300.1 μg L-1). Moreover, urea production increased to 1261.2 μg L-1 when the two yeasts were co-cultured in a simulated fermentation, where the transcription activity of the CAR1 gene increased by 140% in W. anomalus and decreased by 40% in S. cerevisiae. Our findings confirm that a yeast other than Saccharomyces, namely W. anomalus, contributes more to urea formation in a simulated sorghum fermentation. These findings provide the basis for strategies to control or reduce ethyl carbamate formation.

Simultaneous determination of ethyl carbamate and urea in Korean rice wine by ultra-performance liquid chromatography coupled with mass spectrometric detection

In this study, a rapid method for simultaneous detection of ethyl carbamate (EC) and urea in Korean rice wine was developed. To achieve quantitative analysis of EC and urea, the conditions for Ultra-performance liquid chromatography (UPLC) separation and atmospheric-pressure chemical ionization tandem mass spectrometry (APCI-MS/MS) detection were first optimized. Under the established conditions, the detection limit, relative standard deviation and linear range were 2.83μg/L, 3.75-5.96%, and 0.01-10.0mg/L, respectively, for urea; the corresponding values were 0.17μg/L, 1.06-4.01%, and 1.0-50.0μg/L, respectively, for EC. The correlation between the contents of EC and its precursor urea was determined under specific pH (3.5 and 4.5) and temperature (4, 25, and 50°C) conditions using the developed method. As a result, EC content was increased with greater temperature and lower pH. In Korean rice wine, urea was detected 0.19-1.37mg/L and EC was detected 2.0-7.7μg/L. The method developed in this study, which has the advantages of simplified sample preparation, low detection limits, and good selectivity, was successfully applied for the rapid analysis of EC and urea.

Simultaneous determination of ethyl carbamate and urea in alcoholic beverages by high-performance liquid chromatography coupled with fluorescence detection

On the basis of the similar fluorescence of ethyl carbamate (EC) and urea derivatives, a high-performance liquid chromatography method coupled with fluorescence detection was developed for the simultaneous determination of EC and urea in alcoholic beverages. The chromatographic separation and derivatization conditions of EC and urea were optimized. Under the established conditions, the detection limit, relative standard deviation, linear range, and recovery were 4.8 μg/L, 1.0-4.2%, 10-500 μg/L, and 93.8-104.6%, respectively, for EC; the corresponding values were 0.003 mg/L, 1.2-4.8%, 0.01-100 mg/L, and 90.7-104.8%, respectively, for urea. The method showed satisfactory values for precision, recovery, and sensitivity for both analytes and is well-suited for routine analysis and kinetic studies of the formation of EC from urea alcoholysis in alcoholic beverages.