Ethyl carbamate levels in wine and spirits from markets in Hebei Province, China

The Screening and Isolation of Ethyl-Carbamate-Degrading Strains from Fermented Grains and Their Application in the Degradation of Ethyl Carbamate in Chinese Baijiu

Ethyl carbamate (EC), a 2A carcinogen produced during the fermentation of foods and beverages, primarily occurs in distilled spirits. Currently, most studies focus on strategies for EC mitigation. In the present research, we aimed to screen strains that can degrade EC directly. Here, we report two Candida ethanolica strains (J1 and J116), isolated from fermented grains, which can reduce EC concentrations directly. These two yeasts were grown using EC as the sole carbon source, and they grew well on different carbon sources. Notably, after immobilization with chitosan, the two strains degraded EC in Chinese Baijiu by 42.27% and 27.91% in 24 h (from 253.03 ± 9.89 to 146.07 ± 1.67 and 182.42 ± 5.05 μg/L, respectively), which was better than the performance of the non-immobilized strains. Furthermore, the volatile organic compound content, investigated using gas chromatography-mass spectrometry, did not affect the main flavor substances in Chinese Baijiu. Thus, the yeasts J1 and J116 may be potentially used for the treatment and commercialization of Chinese Baijiu.

Research progress on the application of different controlling strategies to minimizing ethyl carbamate in grape wine

Ethyl carbamate (EC) is a probable carcinogenic compound commonly found in fermented foods and alcoholic beverages and has been classified as a category 2A carcinogen by the International Agency for Research on Cancer (IARC). Alcoholic beverages are one of the main sources of EC intake by humans. Therefore, many countries have introduced a standard EC limit in alcoholic beverages. Wine is the second largest alcoholic beverage in the world after beer and is loved by consumers for its rich taste. However, different survey results showed that the detection rate of EC in wine was almost 100%, while the maximum content was as high as 100 μg/L, necessitating EC content regulation in wine. The existing methods for controlling the EC level in wine mainly include optimizing raw fermentation materials and processes, using genetically engineered strains, and enzymatic methods (urease or urethanase). This review focused on introducing and comparing the advantages, disadvantages, and applicability of methods for controlling EC, and proposes two possible new techniques, that is, changing the fermentation strain and exogenously adding phenolic compounds. In the future, it is hoped that the feasibility of this prospect will be verified by pilot-scale or large-scale application to provide new insight into the regulation of EC during wine production. The formation mechanism and influencing factors of EC in wine were also introduced and the analytical methods of EC were summarized.

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

Ethyl carbamate in Chinese liquor (Baijiu): presence, analysis, formation, and control

Ethyl carbamate (EC) is a genotoxic and carcinogenic compound that is also a by-product of fermented foods (bread, sour milk, soy cheese, etc.) and alcoholic beverages (wine, sake, distilled liquor, etc.). Studies have showed that ethyl carbamate is ingested by humans primarily through the consumption of alcoholic beverages. Many countries have thus established EC limits for alcoholic beverages. Chinese liquor (Baijiu) is a traditional and unique distilled liquor, which has a huge consumption in China due to its excellent color, flavor, and taste. Therefore, the control of EC in Chinese liquor is of great significance. This review summarized for the first time the progress in presence level, analysis method, formation mechanism, and elimination strategy of EC of Chinese liquor in recent decades. KEY POINTS: • GC-MS and HPLC are the main methods to quantify EC in Chinese liquor. • EC is formed in the fermentation, distillation, and storage stage. • EC content can be reduced from raw material, microorganism, and production process.

Metabolic engineering of Saccharomyces cerevisiae using the CRISPR/Cas9 system to minimize ethyl carbamate accumulation during Chinese rice wine fermentation

Ethyl carbamate (EC) is a potential carcinogen to humans that is mainly produced through the spontaneous reaction between urea and ethanol during Chinese rice wine brewing. We metabolically engineered a strain by over-expressing the DUR3 gene in a previously modified strain using an improved CRISPR/Cas9 system to further decrease the EC level. Homologous recombination of the DUR3 over-expression cassette was performed at the HO locus by individual transformation of the constructed plasmid CRISPR-DUR3-gBlock-HO, generating the engineered strain N85^DUR1,2/DUR3-c. Consequently, the DUR3 expression level was significantly enhanced in the modified strain, resulting in increased utilization of urea. The brewing test showed that N85^DUR1,2/DUR3-c reduced urea and EC concentrations by 92.0% and 58.5%, respectively, compared with those of the original N85 strain. Moreover, the engineered strain showed good genetic stability in reducing urea content during the repeated brewing experiments. Importantly, the genetic manipulation had a negligible effect on the growth and fermentation characteristics of the yeast strain. Therefore, the constructed strain is potentially suitable for application to reduce urea and EC contents during production of Chinese rice wine. KEY POINTS: • An efficient CRISPR vector was constructed and applied for DUR3 over-expression. • Multi-modification of urea cycle had synergistic effect on reducing EC level. • Fermentation performance of engineered strain was similar with the parental strain. • No residual heterologous genes were left in the genome after genetic manipulation. • An efficient CRISPR vector was constructed and applied for DUR3 over-expression. • Multi-modification of urea cycle had synergistic effect on reducing EC level. • Fermentation performance of engineered strain was similar with the parental strain. • No residual heterologous genes were left in the genome after genetic manipulation.

A Comprehensive Review of Spirit Drink Safety Standards and Regulations from an International Perspective

Standards and regulations related to spirit drinks have been established by different countries and international organizations to ensure the safety and quality of spirits. Here, we introduce the principles of food safety and quality standards for alcoholic beverages and then compare the key indicators used in the distinct standards of the Codex Alimentarius Commission, the European Union, the People's Republic of China, the United States, Canada, and Australia. We also discuss in detail the "maximum level" of the following main contaminants of spirit drinks: methanol, higher alcohols, ethyl carbamate, hydrocyanic acid, heavy metals, mycotoxins, phthalates, and aldehydes. Furthermore, the control measures used for potential hazards are introduced. Harmonization of the current requirements based on comprehensive scope analysis and the risk assessment approach will enhance both the trade and quality of distilled spirits. This review article provides valuable information that will enable producers, traders, governments, and researchers to increase their knowledge of spirit drink safety requirements, control measures, and research trends.

Exposure assessment and risk characterisation of ethyl carbamate from Korean traditional fermented rice wine, Takju and Yakju

Ethyl carbamate is one of the most hazardous chemicals naturally occurring in food, and is present in alcoholic beverages. Korean traditional rice wine, Takju and Yakju, is frequently consumed in Korea, but there have been no studies characterising the risks of ethyl carbamate in these products. In order to assess and characterise the exposure risk of ethyl carbamate in Korean traditional rice wines, ethyl carbamate was investigated by means of GC-MS. The analytical methods were optimised and validated through determining linearity, detection limit, quantification limit, recovery and precision. A total of 283 traditional Korean rice wines, including 175 Takju and 108 Yakju samples, were analysed. Exposure assessment was performed by factoring in ethyl carbamate content, daily consumption and body weight. Daily exposures of ethyl carbamate were estimated for adults in four age groups, and risks of ethyl carbamate were characterised by the margin of exposure, which is more than 10 000. Based on this study, the risks of ethyl carbamate in Korean traditional rice wine were shown to be of low concern.

Formation of ethyl carbamate and changes during fermentation and storage of yellow rice wine

Ethyl carbamate (EC) was analyzed during yellow rice wine production and storage. EC increased slowly during fermentation and rapidly after frying and sterilization. Less amount of EC was formed when cooled rapidly to 30 °C than when cooled naturally. High temperature and long storage time increased EC formation. After 400 days storage, EC increased from 74.0 to 84.2, 131.8 and 509.4 μg/kg at 4 °C, room temperature and 37 °C, respectively, and there was significantly difference between the fried wine and the wine on sale from 2011 (p<0.01). Urea increased during yellow rice wine fermentation and was above 20 mg/kg after the wine was fried; urea contributed to EC formation when the fried wine was cooled slowly. These results indicate that it is necessary for industry to optimize the wine frying conditions, such as temperature, time and cooling process in order to decrease EC formation.

A survey of levels of ethyl carbamate in alcoholic beverages in 2009-2012, Hebei Province, China

Results of a survey of levels of ethyl carbamate (EC) (urethane) in alcoholic beverages carried out in four successive years from 2009 to 2012 by gas chromatography-mass spectrometry (GC/MS) are presented. The beverages were purchased for sampling from Hebei Province of China, including eight main areas of production. The samples comprised wines (n = 212), grain spirits (n = 143) and wine sauces (n = 164). The data show that the average EC content in these kinds of alcoholic beverages remains nearly constant over the years. The results provide valuable data for food authorities to establish maximum limits for EC in China.

Rapid Quantification of Ethyl Carbamate in Spirits Using NMR Spectroscopy and Chemometrics

Ethyl carbamate (EC, urethane, C2H5OCONH2) is a genotoxic carcinogen and is regularly found in fermented food products including alcoholic beverages. In this study, the rapid method of nuclear magnetic resonance (NMR) spectroscopy in combination with partial least squares (PLS) regression is applied for the first time to the analysis of ethyl carbamate in stone fruit spirits () and unrecorded alcohols () (analysis time only 15 min per sample). The PLS procedure was validated using an independent set of samples (, ,  mg/L) in comparison to reference GC/MS/MS results. The NMR method was found to outperform other screening techniques based on NIR or FTIR regarding sensitivity and selectivity. The major advantage over GC/MS/MS, besides the reduced time of instrumental analysis, is that no sample preparation besides addition of buffer with internal standard is required, while for GC/MS/MS labour-intensive sample extraction is necessary prior to measurement.