Formation and hazard of ethyl carbamate and construction of genetically engineered Saccharomyces cerevisiae strains in Huangjiu (Chinese grain wine)

Huangjiu, a well-known conventional fermented Chinese grain wine, is widely consumed in Asia for its distinct flavor. Trace amounts of ethyl carbamate (EC) may be generated during the fermentation or storage process. The International Agency for Research on Cancer elevated EC to a Class 2A carcinogen, so it is necessary to regulate EC content in Huangjiu. The risk of intake of dietary EC is mainly assessed through the margin of exposure (MOE) recommended by the European Food Safety Authority, with a smaller MOE indicating a higher risk. Interventions are necessary to reduce EC formation. As urea, one of the main precursors of EC formation in Huangjiu, is primarily produced by Saccharomyces cerevisiae through the catabolism of arginine, the construction of dominant engineered fermentation strains is a favorable trend for the future production and application of Huangjiu. This review summarized the formation and carcinogenic mechanism of EC from the perspectives of precursor substances, metabolic pathways after ingestion, and risk assessment. The methods of constructing dominant S. cerevisiae strains in Huangjiu by genetic engineering technology were reviewed, which provided an important theoretical basis for reducing EC content and strengthening practical control of Huangjiu safety, and the future research direction was prospected.

Ethyl Carbamate in Fermented Food Products: Sources of Appearance, Hazards and Methods for Reducing Its Content

Ethyl carbamate, the ethyl ester of carbamic acid, has been identified in fermented foods and alcoholic beverages. Since ethyl carbamate is a probable human carcinogen, reduction of its content is important for food safety and human health. In alcoholic beverages, ethyl carbamate is mostly formed from the reaction of ethanol with urea, citrulline and carbamyl phosphate during fermentation and storage. These precursors are generated from arginine metabolism by wine yeasts and lactic acid bacteria. This review summarizes the mechanisms of ethyl carbamate formation, its impact on human health and methods used in winemaking to minimize its content. These approaches include genetic modification of Saccharomyces cerevisiae wine strains targeting pathways of arginine transport and metabolism, the use of lactic acid bacteria to consume arginine, direct degradation of ethyl carbamate by enzymes and microorganisms, and different technological methods of grape cultivation, alcoholic fermentation, wine aging, temperature and duration of storage and transportation.

The Spirit of Cachaça Production: An Umbrella Review of Processes, Flavour, Contaminants and Quality Improvement

This review provides a comprehensive analysis of the production, classification, and quality control of cachaça, a traditional Brazilian sugarcane spirit with significant cultural importance. It explores the fermentation and distillation of sugarcane juice, the ageing process in wooden containers, and the regulatory aspects of cachaça labelling. It emphasises the role of quality control in maintaining the spirit's integrity, focusing on monitoring copper levels in distillation stills. Ethyl carbamate (EC), a potential carcinogen found in cachaça, is investigated, with the study illuminating factors influencing its formation and prevalence and the importance of its vigilant monitoring for ensuring safety and quality. It also underscores the control of multiple parameters in producing high-quality cachaça, including raw material selection, yeast strains, acidity, and contaminants. Further, the impact of ageing, wood cask type, and yeast strains on cachaça quality is examined, along with potential uses of vinasse, a cachaça by-product, in yeast cell biomass production and fertigation. A deeper understanding of the (bio)chemical and microbiological reactions involved in cachaça production is essential to facilitate quality control and standardisation of sensory descriptors, promoting global acceptance of cachaça. Continued research will address safety concerns, improve quality, and support the long-term sustainability and success of the cachaça industry.

A Nationwide Survey and Risk Assessment of Ethyl Carbamate Exposure Due to Daily Intake of Alcoholic Beverages in the Chinese General Population

Ethyl carbamate (EC) is carcinogenic, and, in China, oral intake of EC mainly occurs as a result of the consumption of alcoholic beverages. To obtain the latest EC intake and risk analysis results for the general population in China, the China National Center for Food Safety Risk Assessment (CFSA) conducted the sixth total diet study (TDS) as a platform to analyze EC contents and exposure due to the intake of alcoholic beverages. A total of 100 sites in 24 provinces were involved in the collection and preparation of alcohol mixture samples for the sixth TDS. There were 261 different types of alcohol collected across the country, based on local dietary menus and consumption survey results. Ultimately, each province prepared a mixed sample by mixing their respective samples according to the percentage of local consumption. The EC levels of these twenty-four mixed samples were determined using our well-validated gas chromatography-mass spectrometry (GC-MS) method. The values ranged from 1.0 μg/kg to 33.8 μg/kg, with 10.1 μg/kg being the mean. China's EC daily intake ranged from 0.001 ng/kg bw/d to 24.56 ng/kg bw/d, with a mean of 3.23 ng/kg bw/d. According to the margin of exposure (MOE), virtually safe dose (VSD), and T25 risk assessments of the carcinogenicity of EC, the mean lifetime cancer risk for the Chinese population was 9.8 × 104, 1.5 × 10-7, and 8.6 × 10-8, respectively. These data show that the carcinogenicity of EC in the general Chinese population due to alcoholic intake is essentially minimal.

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.

Peptide-Based Molecularly Imprinted Polymer: A Visual and Digital Platform for Specific Recognition and Detection of Ethyl Carbamate

A visual and digital platform was constructed by peptide-based molecularly imprinted polymers (PMIPs) for specific recognition and detection of ethyl carbamate (EC). Here, the optosensing core was creatively constructed by the covalent assembly of dipeptides (H-Phe-Phe-OH) and genipin biomolecules for high fluorescence quantum yield and dual-signal response capability. MIPs were wrapped in the shell of the optosensing core for selectivity of EC from actual samples of alcoholic beverages. The genipin-FF nanoparticles (GFPNs)@PMIPs exhibited dual-band red-blue fluorescence image with a low detection limit of 0.817 and 1.65 μg L^-1, respectively, in the optimal linear range of 2-240 μg L^-1. The accuracy of this method was verified by the spiked recovery experiment, and a good recovery from 83.97 to 106.75% of the proposed optosensing method was obtained. In addition, a smartphone application was coupled with GFPNs@PMIPs to realize online real-time detection of EC. With the addition of EC, the color change of G and B values was negligible compared with the R value. This work also provides a potential method for on-site visual detection of analytes.

Simulation and Control of the Formation of Ethyl Carbamate during the Fermentation and Distillation Processes of Chinese Baijiu

Baijiu is a popular alcoholic beverage with a long history in China. However, the widespread presence of the ethyl carbamate (EC) carcinogen has raised many food safety concerns. To date, the main precursors of EC and its formation process have not been determined, resulting in difficulty controlling EC in Baijiu. In this study, the main precursors of EC are identified as urea and cyanide during the process of brewing for different flavors of Baijiu, while the dominant stage in which EC formation occurs is during the process of distillation rather than fermentation. In addition, the effects of temperature, pH value, alcohol concentration and metal ions on the formation of EC are confirmed. In the following study, the main precursor of EC is identified as cyanide during the process of distillation, and a combination of optimizing the distillation device and adding copper wire is proposed. Furthermore, the effect of this novel strategy is examined in gaseous reactions between cyanide and ethanol, reducing the concentration of EC by 74.0%. Finally, the feasibility of this strategy is verified in simulated distillations of fermented grains, reducing the formation of EC by 33.7-50.2%. This strategy has great application potential in industrial production.

Reduction of Ethyl Carbamate in an Alcoholic Beverage by CRISPR/Cas9-Based Genome Editing of the Wild Yeast

Ethyl carbamate (EC) is a naturally occurring substance in alcoholic beverages from the reaction of ethanol with urea during fermentation and storage. EC can cause dizziness and vomiting when consumed in small quantities and develop kidney cancer when consumed in excess. Thus, the reduction of EC formation in alcoholic beverages is important for food safety and human health. One of the strategies for reducing EC contents in alcoholic beverages is developing a new yeast starter strain to enable less formation of EC during fermentation. In this study, we isolated a polyploid wild-type yeast Saccharomyces cerevisiae strain from the Nuruk (Korean traditional grain-based inoculum of wild yeast and mold) and developed a starter culture by genome engineering to reduce EC contents in alcoholic beverages. We deleted multiple copies of the target genes involved in the EC formation in the S. cerevisiae by a CRISPR/Cas9-based genome editing tool. First, the CAR1 gene encoding for the arginase enzyme responsible for the formation of urea was completely deleted in the genome of S. cerevisiae. Additionally, the GZF3 gene encoding the transcription factor controlling expression levels of several genes (DUR1, 2, and DUR3) related to urea absorption and degradation was deleted in S. cerevisiae to further reduce the EC formation. The effects of gene deletion were validated by RT-qPCR to confirm changes in transcriptional levels of the EC-related genes. The resulting strain of S. cerevisiae carrying a double deletion of CAR1 and GZF3 genes successfully reduced the EC contents in the fermentation medium without significant changes in alcohol contents and fermentation profiles when compared to the wild-type strain. Finally, we brewed the Korean traditional rice wine Makgeolli using the double deletion strain of S. cerevisiae dCAR1&GZF3, resulting in a significant reduction of the EC content in Makgeolli up to 41.6% when compared to the wild-type strain. This study successfully demonstrated the development of a starter culture to reduce the EC formation in an alcoholic beverage by CRISPR/Cas9 genome editing of the wild yeast.

R-SYB082 and its application in degradation of ethyl carbamate in Chinese rice wine (Huangjiu)

BACKGROUND

Ethyl carbamate (EC) is a potential carcinogen existing in fermented foods such as Chinese rice wine (Huangjiu). Since urea is an important precursor of EC, the degradation of urea could be an effective way to reduce EC in foods.

RESULTS

In this study, an Enterobacter sp. R-SYB082 with acid urea degradation characteristics was obtained through microbial screening. Further research isolated a new acid urea-degrading enzyme from R-SYB082 strain - ureidoglycolate amidohydrolase (UAH) - which could degrade EC directly. The cloning and expression of UAH in Escherichia coli BL21 (DE3) suggested that the activity of urea-degrading enzyme reached 3560 U L^-1 , while urethanase activity reached 2883 U L^-1 in the optimal fermentation condition. The enzyme had the dual ability of degrading substrate urea and product EC. The removal rate of EC in Chinese rice wine could reach 90.7%.

CONCLUSION

This study provided a new method for the integrated control of EC in Chinese rice wine and other fermented foods. © 2022 Society of Chemical Industry.

Sequence and Structure-Guided Engineering of Urethanase from Agrobacterium tumefaciens d3 for Improved Catalytic Activity

The amidase from Agrobacterium tumefaciens d3 (AmdA) degrades the carcinogenic ethyl carbamate (EC) in alcoholic beverages. However, its limited catalytic activity hinders practical applications. Here, multiple sequence alignment was first used to predict single variants with improved activity. Afterward, AlphaFold 2 was applied to predict the three-dimensional structure of AmdA and 21 amino acids near the catalytic triad were randomized by saturation mutagenesis. Each of the mutation libraries was then screened, and the improved single variants were combined to obtain the best double variant I97L/G195A that showed a 3.1-fold increase in the urethanase activity and a 1.5-fold increase in ethanol tolerance. MD simulations revealed that the mutations shortened the distance between catalytic residues and the substrate and enhanced the occurrence of a critical hydrogen bond in the catalytic pocket. This study displayed a useful strategy to engineer an amidase for the improvement of urethanase activity, and the variant obtained provided a good candidate for applications in the food industry.

Citrulline Accumulation Mechanism of Pediococcus acidilactici and Weissella confusa in Soy Sauce and the Effects of Phenolic Compound on Citrulline Accumulation

Citrulline is one of the major precursors of ethyl carbamate in soy sauce, and the accumulation of citrulline is attributed to the metabolism of arginine by bacteria with the arginine deiminase (ADI) pathway. However, key strains and factors affecting citrulline accumulation are not yet clear. In this study, two key strains of Pediococcus acidilactici and Weissella confusa were isolated from soy sauce moromi, and the regularity of citrulline formation was studied. Results showed that the conversion rates from arginine to citrulline (A/C rate) and the citrulline accumulation ability of W. confusa and P. acidilactici significantly increased in the presence of different concentrations of NaCl, indicating that salt stress was the main factor for citrulline accumulation. The inconsistent expression of arc genes by salt stress was the reason for citrulline accumulation for P. acidilactici, but for W. confusa, it may be due to the influence of arginine/citrulline on the transportation system: the intracellular citrulline could neither transport to extracellular space nor convert into ornithine. Environmental factors greatly influenced citrulline accumulation of the two key bacteria; A/C rate and citrulline formation in both strains decreased at low temperature (15°C) under high salt stress, but opposite effects were observed for the two key strains under anaerobic light condition. Moreover, quercetin and gallic acid significantly decreased the A/C rate and citrulline accumulation ability of the two key strains. The optimal quercetin and gallic acid as suggested by simulation experiment were 100 and 10 mg/l, respectively, and the lowest A/C rate of 28.4% and citrulline level of 1326.7 mg/l were achieved in the simulation system. This study explored the main factors for citrulline formation by the two key strains and proposed a targeted way to control citrulline in soy sauce.

Evaluation of Nitrite, Ethyl Carbamate, and Biogenic Amines in Four Types of Fermented Vegetables

Nitrite, ethyl carbamate, and biogenic amines in fermented vegetables are considered harmful compounds. In this study, the concentration of the nitrite, ethyl carbamate, and biogenic amines in four different varieties of fermented vegetables in China was determined. The results show that the nitrite concentration in the fermented cabbage was the highest, followed by fermented mustard, fermented bamboo, and fermented radish. Additionally, nitrite concentration in two fermented cabbage samples and one fermented mustard sample exceeded the maximum allowed residue limit (20 mg/kg) suggested by China’s National Food Safety Standards. However, only one fermented cabbage sample had a very low level of ethyl carbamate (<10 μg/kg). Otherwise, higher biogenic amines were found in the samples of fermented cabbage, fermented bamboo, and fermented mustard. Additionally, the concentration of biogenic amines in some samples exceeded the recommended limit. On the contrary, biogenic amines in fermented radish samples were relatively low. Therefore, the concentration of nitrite and biogenic amine should be closely monitored and controlled during the vegetable fermentation processes, especially for the fermentation processes of bamboo, cabbage, and mustard.

Fluorescent sensor based on quantum dots and nano-porphyrin for highly sensitive and specific determination of ethyl carbamate in fermented food

BACKGROUND

Ethyl carbamate (EC) is a potentially toxic carcinogen produced during fermentation and storage of fermented foods, and many countries have set thresholds for its content in food. Therefore, sensitive, rapid and accurate detection of EC is meaningful to ensure the quality of fermented food.

RESULTS

This study introduces a CdTe quantum dots/nano-5,10,15,20-tetrakis (4-methoxyphenyl)-porphyrin (nano TPP-OCH₃ ) fluorescence sensor system detection of EC. The specificity of this sensing mainly relies on a photo-induced electron transfer and electrostatic force interaction between EC and nano TPP-OCH₃ . This sensor presented a linear range of 10 to 1000 μg L^-1 (R²  = 0.9903) with a low detection limit of 7.14 μg L^-1 . Meanwhile, the recovery (91.19-101.09%) and precision [relative standard deviation (RSD) = 0.64-3.05%] of the sensor for the analysis of fermented food (yellow rice wine, soy sauce, Chinese spirits, Pu-erh tea) samples were good and could meet the requirements of practical detection. Moreover, the detection results of fermented food (yellow rice wine, soy sauce, Chinese spirits, Pu-erh tea) samples by this sensor are basically consistent with those of high-performance liquid chromatography with fluorescence detector (HPLC-FLD).

CONCLUSION

This method was expected to provide a potential platform for sensitive and accurate detection of EC in food safety monitoring, which would provide knowledge of the flavor and quality related to fermented food. © 2021 Society of Chemical Industry.

Ethyl carbamate in retail market condiments and risk assessment of its dietary exposure for the Korean population

Ethyl carbamate (EC), a potential human dietary carcinogen, is found in fermented foods including the fermented soybean-based condiments, the major part of the Korean diet. Therefore, it is expected that their EC contents might pose health risks. Herein, we collected 111 condiments and estimated their EC contents via gas chromatography-mass spectrometry. Further, dietary intake of EC was evaluated, and the risk levels were assessed via the margin of exposure (MOE) approach and excess cancer risk assessment. EC contents of the condiments ranged from not detectable to 39.47 μg/kg, and the daily EC exposure ranged from 1.4 to 2.0 ng/kg BW per day, depending on gender and age groups in Korea. Of the condiments, soy sauce was the largest contributor to EC exposure. MOE and excess cancer risks for the average consumer were 166,300 and 9.0 × 10^-8, respectively, and those for the consumers in the 95^th percentiles (P95) were 53,504 and 2.8 × 10^-7, respectively, indicating that the risk of exposure to EC is of lower concern in average consumers than heavy consumers. However, the EC exposure from condiments was higher than that in other Asian countries.Abbreviations: EC: ethyl carbamate; GC-MS: gas chromatography-mass spectrometry; MOE: margin of exposure; MRL: maximum residue level; IDL: instrumental detection level; IQL: instrumental quantification level; MDL: method detection level; MQL: method quantification level; EDI: estimated daily intakes; BMDL₁₀: benchmark dose lower confidence limit.

Origin, Succession, and Control of Biotoxin in Wine

Wine is a worldwide alcoholic beverage with antioxidant active substances and complex flavors. Moderate drinking of wine has been proven to be beneficial to health. However, wine has some negative components, such as residual pesticides, heavy metals, and biotoxins. Of these, biotoxins from microorganisms were characterized as the most important toxins in wine. Wine fermentation mainly involves alcoholic fermentation, malolactic fermentation, and aging, which endue wine with complex flavors and even produce some undesirable metabolites. These metabolites cause potential safety risks that are not thoroughly understood. This review aimed to investigate the origin, evolution, and control technology of undesirable metabolites (e.g., ochratoxin A, ethyl carbamate, and biogenic amines) in wine. It also highlighted current wine industry practices of minimizing the number of biotoxins in wine.

New function of polysaccharide from Rubus chingii Hu: protective effect against ethyl carbamate induced cytotoxicity

BACKGROUND

Rubus chingii Hu is a widely cultivated fruit in China and has declared multiple bioactivities including antioxidative activity. Ethyl carbamate (EC), mostly found in fermented food and alcoholic beverages, is a recognized human carcinogen, and researchers have proposed the correlation between oxidative stress and its toxicity. This study acquired the polysaccharide from R. chingii (RP) and explored its effect on EC-induced cytotoxicity using Caco-2 cells as the cell model.

RESULTS

Results showed that RP exhibited protection against EC-induced toxicity by repairing redox imbalance as indicative of mitigated mitochondrial membrane potential collapse, attenuated reactive oxygen species overproduction, and impeded glutathione depletion. Moreover, the structural features of RP were characterized and revealed that it was mainly constituted by galacturonic acid and arabinose, with an average molecular weight of 7.039 × 10⁵  g mol^-1 .

CONCLUSION

Overall, our results provided a new approach dealing with the toxicity caused by EC from the perspective of oxidative stress and described a new potential healthy value of R. chingii Hu, which could contribute to the development of a promising dietary supplement and functional food. © 2020 Society of Chemical Industry.

Effect of Fermentation on Cyanide and Ethyl Carbamate Contents in Cassava Flour and Evaluation of Their Mass Balance during Lab-Scale Continuous Distillation

When cassava is used for the production of distilled spirits through fermentation and distillation, toxic hydrogen cyanide (HCN) is released from linamarin and carcinogenic ethyl carbamate is produced. Herein, cyanide and ethyl carbamate contents were monitored during the fermentation and lab-scale continuous distillation processes. Thereafter, mass balance and the influence of copper chips were evaluated. Results showed that 81.5% of cyanide was removed after fermentation. Use of copper chips completely prevented the migration of cyanide into the distilled spirits, while 88.3% of cyanide migrated from the fermented liquid in the absence of copper chips. Formation of ethyl carbamate was significantly promoted during distillation. Most of the produced ethyl carbamate (73.2%) was transferred into the distilled spirits in the absence of copper chips, only 9.6% of the ethyl carbamate was transferred when copper chips were used. Thus, copper chips effectively prevented the migration of cyanide and ethyl carbamate into the distilled spirts during continuous distillation.

Renal Transcriptomics Reveals the Carcinogenic Mechanism of Ethyl Carbamate in Musalais

INTRODUCTION

Musalais is a traditional fermented wine produced in southern Xinjiang (a province of China) and is protected as a form of national intangible cultural heritage. However, ethyl carbamate (EC), which is naturally produced during the fermentation process, has been shown to induce carcinogenesis and was classified as a group 2A carcinogen by The World Health Organization's International Agency for Research on Cancer.

METHODS

In this work, rats were treated with musalais containing EC at varying contents (0.1, 1, or 10 mg/kg). To evaluate the toxicity of EC in musalais, the liver and kidney of the rats were subjected to transcriptomics sequencing. Differentially expressed genes (DEGs) between treated and untreated rats were identified, and Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analysis were performed on these genes to investigate the biological functions affected by EC in musalais.

RESULTS

The results demonstrated that high EC content in musalais is possibly involved in the regulation of cytochrome P450 metabolism, chemical carcinogenesis, metabolism of xenobiotics by cytochrome P450, Wnt signaling, and p53 signaling by targeting Mgst1, Gstp1, Gsta5, Gsta1, Adh1, Gsta2, and Ccnd1, thereby inducing cancer.

CONCLUSION

The present work predicted the potential carcinogenic mechanism of high EC content in musalais, providing a reference for its safety evaluation.

Effects of the pre-fermentative addition of chitosan on the nitrogenous fraction and the secondary fermentation products of SO2 -free red wines

BACKGROUND

Different red winemaking were carried out to evaluate the effects of the prefermentative addition of chitosan, as an alternative to the use of SO₂ , on the secondary products of alcoholic fermentation, yeast available nitrogen (YAN), biogenic amines and ethyl carbamate.

RESULTS

The wines made with chitosan presented higher total acidity and higher content of tartaric and succinic acids than those made only with SO₂ . The use of chitosan in winemaking resulted in wines with higher glycerol and diacetyl content without increasing the concentration of ethanol, acetic acid, acetaldehyde or butanediol. YAN was lower in wines made with chitosan, which may mean an advantage for the microbial stability of the wines. Furthermore, the use of chitosan at the beginning of alcoholic fermentation did not increase the concentration of biogenic amines or the formation of ethyl carbamate in SO₂ -free red wines.

CONCLUSION

The total or partial substitution of SO₂ for chitosan at the beginning of the alcoholic fermentation gives rise to quality red wines without negatively affecting their nitrogen fraction or their very important secondary fermentation products such as acetic acid or acetaldehyde. © 2020 Society of Chemical Industry.

Quantitative Analysis of Ethyl Carbamate in Distillers Grains Co-products and Bovine Plasma by Gas Chromatography-Mass Spectrometry

Ethyl carbamate (EC) is a fermentation byproduct in foods and beverages and classified as a Group 2A probable human carcinogen. Each year, greater than 40 million metric tons of fermentation co-products from the U.S. ethanol industry are fed to food animals. A gas chromatography-mass spectrometry assay was developed to quantify EC extracted from various distillers grains co-products with a limit of detection at 0.7 ng/g (on an as-fed basis). EC was detected in all the distillers grains co-products surveyed in this study. Corn condensed distillers solubles contained the highest concentration of EC, ranging from 1618 to 2956 ng/g. Concentrations of EC in other types of distillers grains co-products varied from 17 to 917 ng/g. Cattle fed distillers grains co-products that constituted 19-38% of the total feed (as-fed) were found to contain 2-3 ng/mL of EC in blood plasma. No EC was detected in blood plasma from grass-fed control cattle.

[Improving applicability of urease from Bacillus amyloliquefaciens JP-21 by site-directed mutagenesis]

Ethyl carbamate (EC) is a carcinogen detected in fermented foods and alcohol beverages. Excessive intake of EC is possibly harmful to health. Enzymatic degradation is one of the most effective approaches for reducing EC in fermented foods. Urease catalyzes the hydrolysis of both EC and urea. This confers urease a good application prospect in reducing EC and its precursor urea in fermented foods. Currently, degradation of EC in alcohol beverages by urease is inefficient due to its low urethanase activity and poor affinity to EC. Urease from Bacillus amyloliquefaciens JP-21 was successfully expressed in Escherichia coli at the level of 3 292 U/L urease and 227.3 U/L urethanase. Two key residues M326 and M374 were characterized that might block the binding of enzyme to EC, through simulating docking the structure of catalytic subunit UreC of urease with EC. Three mutants (M374A, M374T and M326V) of urease with improved urethanase activity were obtained by performing point saturated mutagenesis approach. Using EC as the substrate, Km values of M374A, M374T and M326V were detected to be 101.8 mmol/L, 129.5 mmol/L and 121.7 mmol/L, respectively, which were decreased by 37.47%-50.82% compared with that of the wild type urease. These mutants can degrade more than 97% of urea in rice wine and mutant M374T shows the highest degradation of EC in rice wine. EC content in rice wine was reduced from 525 μg/L to 393 μg/L by using M374T, and the EC degradation rate of it is 0.97 folds higher than that of the wild type urease. The results are of great significance for engineering the catalytic properties of urease and improving its industrial properties, and lays a good foundation for developing strategies to reducing microbial metabolic ammonia (amine) hazards in fermented foods.

Chinese Yellow Rice Wine Processing with Reduced Ethyl Carbamate Formation by Deleting Transcriptional Regulator Dal80p in Saccharomyces cerevisiae

Ethyl carbamate (EC) is a potential carcinogen that forms spontaneously during Chinese rice wine fermentation. The primary precursor for EC formation is urea, which originates from both external sources and arginine degradation. Urea degradation is suppressed by nitrogen catabolite repression (NCR) in Saccharomyces cerevisiae. The regulation of NCR is mediated by two positive regulators (Gln3p, Gat1p/Nil1p) and two negative regulators (Dal80p/Uga43p, Deh1p/Nil2p/GZF3p). DAL80 revealed higher transcriptional level when yeast cells were cultivated under nitrogen-limited conditions. In this study, when DAL80-deleted yeast cells were compared to wild-type BY4741 cells, less urea was accumulated, and genes involved in urea utilization were up-regulated. Furthermore, Chinese rice wine fermentation was conducted using dal80Δ cells; the concentrations of urea and EC were both reduced when compared to the BY4741 and traditional fermentation starter. The findings of this work indicated Dal80p is involved in EC formation possibly through regulating urea metabolism and may be used as the potential target for EC reduction.

Transposition of IS4 Family Insertion Sequences ISTeha3, ISTeha4, and ISTeha5 into the arc Operon Disrupts Arginine Deiminase System in Tetragenococcus halophilus

Tetragenococcus halophilus, a halophilic lactic acid bacterium, is often used as a starter culture in the manufacturing of soy sauce. T. halophilus possesses an arginine deiminase system, which is responsible for the accumulation of citrulline, the main precursor of the potential carcinogen ethyl carbamate. In this study, we generated five derivatives lacking arginine deiminase activity from T. halophilus NBRC 12172 by UV irradiation. Using these derivatives as a fermentation starter prevented arginine deimination in soy sauce. DNA sequence analysis of the derivatives revealed that novel IS4 family insertion sequences, designated ISTeha3, ISTeha4, and ISTeha5, were transposed into the region around the arginine deiminase (arc) operon in the mutants. These insertion sequences contain a single open reading frame encoding a putative transposase and 13- to 15-bp inverted repeats at both termini, which are adjacent to 7- to 9-bp duplications of the target sequence. Investigation of wild strains isolated from soy sauce mash incapable of arginine deimination also indicated that insertion sequences are involved in the disruption of the arginine deiminase system in T. halophilus IMPORTANCE Insertion sequences play important roles in bacterial evolution and are frequently utilized in mutagenesis systems. However, the intrinsic insertion sequences of tetragenococci are not well characterized. Here, we identified three active insertion sequences of T. halophilus by transposition into the region around the arc operon. This report provides an example of insertion sequence-mediated generation and evolution of T. halophilus and primary information about their characteristics.

[Advances in microbial enzymatic elimination of ethyl carbamate in Chinese rice wine]

Ethyl carbamate (EC), a carcinogenic and teratogenic chemical that is widely distributed in various alcoholic beverages, has attracted much attention. Microbial enzymatic degradation of EC in rice wine is always efficient and attractive. In this review, we summarize the research progress and problems of microbial enzymatic elimination of EC in rice wine from three aspects: the mechanisms of EC formation in rice wine, the research progress of acid urease, and the research progress of urethanase. Then, we propose the corresponding strategies to solve the problems: screening new urethanase with satisfied enzyme properties, food-grade expression and directed evolution of the bifunctional Fe³⁺-dependent acid urease and acid urease used in combination with urethanase to eliminate both urea and EC in rice wine.

Formation of Ethyl Carbamate during the Production Process of Cantonese Soy Sauce

The aim of this work was to clarify the formation of ethyl carbamate (EC) and its influence factors throughout the production process of Cantonese soy sauce. The results showed that EC was not detected in the koji-making and early moromi fermentation stages, but started to be generated when pH of the moromi decreased to about 4.9—at the same time, the levels of ethanol, urea and citrulline increased significantly. Most EC was formed during raw soy sauce hot extraction (40.6%) and sterilization (42.9%) stages. The EC content exhibited the highest correlation with ethanol throughout the whole production process (R = 0.97). The simulation soy sauce produced in laboratory led the same conclusion—moreover, the contents of EC, ethanol and citrulline were higher in soy sauce fermented at 30 °C than in soy sauce fermented at 15 °C. Extraction of raw soy sauce by squeezing contributed little to EC formation. Further research showed that citrulline and ethanol led to significant increases in EC levels in raw soy sauce upon heating. These results indicate that ethanol and citrulline are two critical precursors of EC and that EC is mainly formed during the heat treatment stage of soy sauce.

Assessment of the Pig-a, micronucleus, and comet assay endpoints in rats treated by acute or repeated dosing protocols with procarbazine hydrochloride and ethyl carbamate

The utility and sensitivity of the newly developed flow cytometric Pig-a gene mutation assay have become a great concern recently. In this study, we have examined the feasibility of integrating the Pig-a assay as well as micronucleus and Comet endpoints into acute and subchronic general toxicology studies. Male Sprague-Dawley rats were treated for 3 or 28 consecutive days by oral gavage with procarbazine hydrochloride (PCZ) or ethyl carbamate (EC) up to the maximum tolerated dose. The induction of CD59-negative reticulocytes and erythrocytes, micronucleated reticulocytes in peripheral blood, micronucleated polychromatic erythrocytes in bone marrow, and Comet responses in peripheral blood, liver, kidney, and lung were evaluated at one, two, or more timepoints. Both PCZ and EC produced positive responses at most analyzed timepoints in all tissue types, both with the 3-day and 28-day treatment regimens. Furthermore, comparison of the magnitude of the genotoxicity responses indicated that the micronucleus and Comet endpoints generally produced greater responses with the higher dose, short-term treatments in the 3-day study, while the Pig-a assay responded better to the cumulative effects of the lower dose, but repeated subchronic dosing in the 28-day study. Collectively, these results indicate that integration of several in vivo genotoxicity endpoints into a single routine toxicology study is feasible and that the Pig-a assay may be particularly suitable for integration into subchronic dose studies based on its ability to accumulate the mutations that result from repeated treatments. This characteristic may be especially important for assaying lower doses of relatively weak genotoxicants. Environ. Mol. Mutagen. 60:56-71, 2019. © 2018 Wiley Periodicals, Inc.

Molecular Engineering of Bacillus paralicheniformis Acid Urease To Degrade Urea and Ethyl Carbamate in Model Chinese Rice Wine

Bacillus paralicheniformis urease (BpUrease) has been shown to be a promising biocatalyst for degrading the carcinogenic chemical ethyl carbamate (EC or urethane) in rice wine. However, low EC affinity and catalytic efficiency limit the practical application of BpUrease. In this study, we improved the EC degradation capability of BpUrease by site-saturation mutagenesis (SSM). The best variant L253P/L287N showed a 49% increase in EC affinity, 1027% increase in catalytic efficiency ( k_cat/ K_m), and 583% increase in half-life ( t_1/2) at 70 °C. Homology modeling analysis suggest that mutation of Leu253 to Pro increased the BpUrease EC specificity by affecting the interaction between Arg339 with the catalytic residue His323, while Leu287Asn mutation benefits EC specificity and affinity by changing the interaction networks among the residues in the catalytic pocket. Our results show that the L253P/L287N variant efficiently degraded urea and EC in a model rice wine, making it a good candidate for practical application in the food industry.

Detection of ethyl carbamate in liquors using surface-enhanced Raman spectroscopy

Ethyl carbamate (EC), a potential carcinogen, can be formed during the fermentation and storage of alcoholic beverages. In this work, quantitative detection of EC in alcoholic beverages by using surface-enhanced Raman spectroscopy (SERS) is reported. Flower-shaped silver nanostructure substrates and silver nanocube substrates were prepared and employed as SERS platform. Flower-like silver substrates had better Raman enhancement effect on EC and were selected for further EC detection. In EC SERS spectra based on flower-shaped silver substrates, the strongest and reproducible characteristic band at 857 cm^-1 was chosen for establishing a linear regression model in the concentrations ranging from 10^-5 to 10^-9 M, which effectively extended the application scope of the quantitative model for determination EC. Furthermore, a real alcoholic beverage was tested to verify the feasibility and reliability of the method.

Metabolic Engineering of Four GATA Factors to Reduce Urea and Ethyl Carbamate Formation in a Model Rice Wine System

Urea is the most important precursor of ethyl carbamate (EC), a harmful carcinogenic product, in fermented wines. In this study, the effects of four GATA transcriptional factors (Gln3p, Gat1p, Dal80p ,and Gzf3p) on extracellular urea and EC formation and transcriptional changes in urea degradation related genes ( DUR1,2 and DUR3) were examined. Compared to the WT strain, the Δ gzf3 mutant showed 18.7% urea reduction and exhibited synergistic effects with overexpressed Gln3p_1-653 and Gat1p_1-375 on extracellular urea reduction. Moreover, Δ gzf3+Gln3p_1-653 and Δ gzf3+Gat1p_1-375 showed significant 38.7% and 43.7% decreases in urea concentration and 41.7% and 48.5% decreases in EC concentration, respectively, in a model rice wine system. These results provide a promising way to reduce urea and EC formation during wine fermentation and raise some cues for the regulations of the four GATA transcriptional factors on the expression of individual nitrogen catabolite repression sensitive genes and their related metabolism pathway.

Arginine and Citrulline Catabolic Pathways Encoded by the arc Gene Cluster of Lactobacillus brevis ATCC 367

High concentrations of l-arginine or l-citrulline in the growth medium provided the wine bacterium Lactobacillus brevis with a significant growth advantage. The arginine deiminase pathway (ADI) arc gene cluster of Lactobacillus brevis contains three genes-arcD, arcE1, and arcE2-encoding putative l-arginine/l-ornithine exchangers. Uptake experiments with Lactococcus lactis cells expressing the genes showed that all three transported l-ornithine with affinities in the micromolar range. Similarly, ArcD and ArcE2 transported l-arginine, while ArcE1 transported l-citrulline, an intermediate of the ADI pathway. Chase experiments showed very efficient exchange of l-arginine and l-ornithine by ArcD and ArcE2 and of l-citrulline and l-ornithine by ArcE1. Low affinities (millimolar range) combined with low translocation rates were found for ArcD and ArcE2 with l-citrulline and for ArcE1 with l-arginine. Resting cells of Lactobacillus brevis grown in the presence of l-arginine and l-citrulline rapidly consumed l-arginine and l-citrulline, respectively, while producing ammonia and l-ornithine. About 10% of l-arginine degraded was excreted by the cells as l-citrulline. Degradation of l-arginine and l-citrulline was not subject to carbon catabolite repression by glucose in the medium. At a high medium pH, l-citrulline in the medium was required for induction of the l-citrulline degradation pathway. Pathways are proposed for the catabolic breakdown of l-arginine and l-citrulline that merge at the level of ornithine transcarbamylase in the ADI pathway. l-Arginine uptake is catalyzed by ArcD and/or ArcE2, l-citrulline by ArcE1. l-Citrulline excretion during l-arginine breakdown is proposed to be catalyzed by ArcD and/or ArcE2 through l-arginine/l-citrulline exchange.IMPORTANCELactobacillus brevis, a bacterium isolated from wine, as well as other food environments, expresses a catabolic pathway for the breakdown of l-citrulline in the medium that consists of the l-citrulline/l-ornithine exchanger ArcE1 and part of the catabolic arginine deiminase (ADI) pathway enzymes. The proposed pathways for l-arginine and l-citrulline breakdown provide a mechanism for l-citrulline accumulation in fermented food products that is the precursor of the carcinogen ethyl carbamate.

New Approach of QuEChERS and GC-MS Triple-Quadrupole for the Determination of Ethyl Carbamate Content in Brazilian cachaças

Cachaça is a popular spirit produced in Brazil, obtained by distillation of fermented sugar cane. Among the contaminants arising from production, ethyl carbamate is a carcinogenic compound that occurs naturally in fermented foods and beverages; in Brazil, the maximum limit established by current legislation is 150 µg L⁻¹. Quality control is usually performed using gas chromatography; however, robustness and reproducibility of quantitative results may be severely impaired, as the addition of 6–30 g L⁻¹ of sucrose is a common procedure for taste standardization, directly interfering in the results. This work describes the development of a novel method to improve ethyl carbamate quantification in cachaças using a new approach of QuEChERS extraction based on salting-out phenomenon, to effectively separate ethanol from sugar-containing water. Eighteen different brands of cachaça were analyzed. The proposed methodology was able to eliminate components that contaminate the sample flow path in the gas chromatography system, while improving precision and accuracy by using a triple-quadrupole approach, in comparison with the methodology usually employed: direct analysis of cachaça samples with no sample prep. Results indicate that this approach is more effective due to the removal of sugar content, with no impact in costs per analysis.

[Stability enhancement of urethanase from Lysinibacillus fusiformis by site-directed mutagenesis]

Ethyl carbamate as a potential carcinogen commonly exists in traditional fermented foods and beverages. Enzymatic removal of ethyl carbamate from fermented foods and beverages is an efficient and safe method. In this study, we mutated urethanase from Lysinibacillus fusiformis SC02 on the Q328 site through computer aided design approaches. The half-life of resulting mutants Q328C and Q328V was detected to be 7.46 and 1.96 folds higher than that of the original enzyme, and Q328R presented better thermal-tolerance than the original urethanase when incubated at high temperature. The tolerance of Q328C to ethanol and acid also increased when compared with that of the original enzyme. The stability and tolerance to acid and ethanol of urethanase could be improved by modification on its Q328 site.

Accumulation of Citrulline by Microbial Arginine Metabolism during Alcoholic Fermentation of Soy Sauce

Citrulline, the major precursor of ethyl carbamate in soy sauce, is an intermediate catabolite of arginine produced by bacteria present in soy sauce moromi mash. Pediococcus acidilactici is responsible for the formation of citrulline during the lactic acid fermentation process of soy sauce. However, citrulline accumulation during the alcoholic fermentation process and the corresponding bacteria involved have not been identified. Salt-tolerant, arginine-utilizing bacteria were isolated from moromi mash during the alcoholic fermentation process. Under normal cultivation conditions, arginine utilization by these strains did not contribute to citrulline accumulation. However, the conversion of arginine to citrulline by these bacteria increased when cultivated during the alcoholic fermentation process. Additionally, the ethanol-enhanced solubility of free fatty acids in moromi mash stimulated the accumulation of citrulline. Staphylococcus exhibited the highest capability in the conversion of arginine to citrulline.

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.

Ethyl Carbamate Formation Regulated by Lactic Acid Bacteria and Nonconventional Yeasts in Solid-State Fermentation of Chinese Moutai-Flavor Liquor

This study aimed to identify specific microorganisms related to the formation of precursors of EC (ethyl carbamate) in the solid-state fermentation of Chinese Moutai-flavor liquor. The EC content was significantly correlated with the urea content during the fermentation process (R² = 0.772, P < 0.01). Differences in urea production and degradation were found at both species and functional gene levels by metatranscriptomic sequencing and culture-dependent analysis. Lactobacillus spp. could competitively degrade arginine through the arginine deiminase pathway with yeasts, and most Lactobacillus species were capable of degrading urea. Some dominant nonconventional yeasts, such as Pichia, Schizosaccharomyces, and Zygosaccharomyces species, were shown to produce low amounts of urea relative to Saccharomyces cerevisiae. Moreover, unusual urea degradation pathways (urea carboxylase, allophanate hydrolase, and ATP-independent urease) were identified. Our results indicate that EC precursor levels in the solid-state fermentation can be controlled using lactic acid bacteria and nonconventional yeasts.

Effect of Microbial Interaction on Urea Metabolism in Chinese Liquor Fermentation

Urea is the primary precursor of the carcinogen ethyl carbamate in fermented foods. Understanding urea metabolism is important for controlling ethyl carbamate production. Using Chinese liquor as a model system, we used metatranscriptome analysis to investigate urea metabolism in spontaneous food fermentation processes. Saccharomyces cerevisiae was dominant in gene transcription for urea biosynthesis and degradation. Lysinibacillus sphaericus was dominant for urea degradation. S. cerevisiae degraded 18% and L. sphaericus degraded 13% of urea in their corresponding single cultures, whereas they degraded 56% of urea in coculture after 12 h. Compared to single cultures, transcription of CAR1, DAL2, and argA, which are related to urea biosynthesis, decreased by 51, 36, and 69% in coculture, respectively. Transcription of DUR1 and ureA, which are related to urea degradation, increased by 227 and 70%, respectively. Thus, coexistence of the two strains promoted degradation of urea via transcriptional regulation of genes related to urea metabolism.

CRISPR/Cas9 System as a Valuable Genome Editing Tool for Wine Yeasts with Application to Decrease Urea Production

An extensive repertoire of molecular tools is available for genetic analysis in laboratory strains of S. cerevisiae. Although this has widely contributed to the interpretation of gene functionality within haploid laboratory isolates, the genetics of metabolism in commercially-relevant polyploid yeast strains is still poorly understood. Genetic engineering in industrial yeasts is undergoing major changes due to Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and CRISPR-associated protein (Cas) engineering approaches. Here we apply the CRISPR/Cas9 system to two commercial “starter” strains of S. cerevisiae (EC1118, AWRI796), eliminating the CAN1 arginine permease pathway to generate strains with reduced urea production (18.5 and 35.5% for EC1118 and AWRI796, respectively). In a wine-model environment based on two grape musts obtained from Chardonnay and Cabernet Sauvignon cultivars, both S. cerevisiae starter strains and CAN1 mutants completed the must fermentation in 8–12 days. However, recombinant strains carrying the can1 mutation failed to produce urea, suggesting that the genetic modification successfully impaired the arginine metabolism. In conclusion, the reduction of urea production in a wine-model environment confirms that the CRISPR/Cas9 system has been successfully established in S. cerevisiae wine yeasts.

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.

A Bacillus paralicheniformis Iron-Containing Urease Reduces Urea Concentrations in Rice Wine

Urease, a nickel-containing metalloenzyme, was the first enzyme to be crystallized and has a prominent position in the history of biochemistry. In the present study, we identified a nickel urease gene cluster, ureABCEFGDH, in Bacillus paralicheniformis ATCC 9945a and characterized it in Escherichia coli Enzymatic assays demonstrate that this oxygen-stable urease is also an iron-containing acid urease. Heterologous expression assays of UreH suggest that this accessory protein is involved in the transmembrane transportation of nickel and iron ions. Moreover, this iron-containing acid urease has a potential application in the degradation of urea in rice wine. The present study not only enhances our understanding of the mechanism of activation of urease but also provides insight into the evolution of metalloenzymes.IMPORTANCE An iron-containing, oxygen-stable acid urease from B. paralicheniformis ATCC 9945a with good enzymatic properties was characterized. This acid urease shows activities toward both urea and ethyl carbamate. After digestion with 6 U/ml urease, approximately 92% of the urea in rice wine was removed, suggesting that this urease has great potential in the food industry.

The Combined Use of Schizosaccharomyces pombe and Lachancea thermotolerans-Effect on the Anthocyanin Wine Composition

The most popular methodology to make red wine is through the combined use of Saccharomyces cerevisiae yeast and lactic acid bacteria, for alcoholic fermentation and malolactic fermentation respectively. This classic winemaking practice produces stable red wines from a microbiological point of view. This study aims to investigate a recent red winemaking biotechnology, which through the combined use of Lachancea thermotolerans and Schizosaccharomyces pombe is used as an alternative to the classic malolactic fermentation. In this new methodology, Schizosaccharomycespombe totally consumes malic acid, while Lachancea thermotolerans produces lactic acid, avoiding excessive deacidification of musts with low acidity in warm viticulture areas such as Spain. This new methodology has been reported to be a positive alternative to malolactic fermentation in low acidity wines, since it has the advantage to produce wines with a more fruity flavor, less acetic acid, less ethyl carbamate originators and less biogenic amines than the traditional wines produced via conventional fermentation techniques. The study focuses on unexplored facts related to this novel biotechnology such as color and anthocyanin profile.

Occurrence of ethyl carbamate in three types of Chinese wines and its possible reasons

A total of 75 wines including 30 white wines, 31 red wines, and 14 sparkling wines were obtained from several regions in China (Sinkiang, Tonghua, Huailai, Yantai, Changli, Shanxi, Gansu, and Ningxia). Ethyl carbamate (EC) was detected by gas chromatography mass spectrometry. The EC concentration ranged from less than 1.16 to 38.56 μg/L, and the concentrations in 17 wines exceeded the U.S. limit for table wines (15 μg/L). The concentrations of EC increased in the order of white, red, and sparkling wines with the corresponding mean concentrations of 6.12, 9.22, and 14.03 μg/L. The relationship between EC concentration and wine type suggested that EC concentrations in wines might be affected by vinification patterns, most likely due to the difference between EC precursors in different vinification processes. This work provides a novel clue for EC contamination in different wines.

Formation of ethyl carbamate in Goji wines: Effect of Goji fruit composition

Ethyl carbamate (EC) is a multisite carcinogen widely occurring in alcoholic beverages. In this investigation, solid-phase extraction combined with gas chromatography mass spectrometry was employed to determine EC contents during the fermentation and storage processes, and the effects of Goji varieties on its formation were also examined. The results indicated that natural and potential EC contents were significantly affected by the varied composition of Goji fruits. The analysis of chemical properties showed differences in hundred-grain weight, water contents, amino acids, and nitrogen-to-carbon ratio for Goji berries. Citrulline was completely degraded although it is routinely considered as a non-preferred nitrogen for yeasts. Due to compositional differences, Goji wines accumulated distinct urea levels that positively correlated with the potential EC contents. Furthermore, the temperature in both the production processes highly influenced EC formation. These results contribute to a more comprehensive understanding of EC formation, and in turn, controlling EC in the Goji wine matrix.

Evaluation of the impact on food safety of a Lactobacillus coryniformis strain from pickled vegetables with degradation activity against nitrite and other undesirable compounds

Four strains of lactic acid bacteria showing antimicrobial activity against some food-spoilage microorganisms or pathogens, including both Gram-negative and -positive strains, were isolated from naturally fermented pickled vegetables and a traditional cheese product. Among these isolates, Lactobacillus coryniformis strain BBE-H3, characterised previously to be a non-biogenic amine producer, showed a high level of activity in degrading sodium nitrite and exhibited the ability to eliminate ethyl carbamate and one of its precursors, urea. The antimicrobial substance produced by L. coryniformis BBE-H3 was found to be active at an acidic pH range of 4.0-4.5. The antimicrobial activity of this strain decreased differentially after treatment with proteolytic enzymes (pepsin, papain, trypsin and proteinase K), implying this growth inhibitory compound is either a protein or a polypeptide. The results of this study show the suitability of L. coryniformis BBE-H3 as a starter in food manufacturing processes, and demonstrate its potential role in eliminating food origin carcinogens such as sodium nitrite and ethyl carbamate.

Cyanate as an Active Precursor of Ethyl Carbamate Formation in Sugar Cane Spirit

The thermodynamic and kinetic aspects of ethyl carbamate (EC) formation through the reaction between cyanate and ethanol were investigated. The rate constant values for cyanate ion decay and EC formation are (8.0 ± 0.4) × 10(-5) and (8.9 ± 0.4) × 10(-5) s(-1), respectively, at 25 °C in 48% aqueous ethanolic solution at pH 4.5. Under the investigated experimental conditions, the rate constants are independent of the ethanol and cyanate concentrations but increase as the temperature increases (ΔH1(⧧) = 19.4 ± 1 kcal/mol, ΔS1(⧧) = −12.1 ± 1 cal/K, and ΔG1(⧧) = 23.0 ± 1 kcal/mol) and decrease as the solution pH increases. According to molecular modeling (DFT) that was performed to analyze the reaction mechanism, the isocyanic acid (HNCO) is the active EC precursor. The calculated ΔG1(⧧), ΔH1(⧧), and ΔS1(⧧) values are in very good agreement with the experimental ones.

Combine Use of Selected Schizosaccharomyces pombe and Lachancea thermotolerans Yeast Strains as an Alternative to the Traditional Malolactic Fermentation in Red Wine Production

Most red wines commercialized in the market use the malolactic fermentation process in order to ensure stability from a microbiological point of view. In this second fermentation, malic acid is converted into l-lactic acid under controlled setups. However this process is not free from possible collateral effects that on some occasions produce off-flavors, wine quality loss and human health problems. In warm viticulture regions such as the south of Spain, the risk of suffering a deviation during the malolactic fermentation process increases due to the high must pH. This contributes to produce wines with high volatile acidity and biogenic amine values. This manuscript develops a new red winemaking methodology that consists of combining the use of two non-Saccharomyces yeast strains as an alternative to the traditional malolactic fermentation. In this method, malic acid is totally consumed by Schizosaccharomyces pombe, thus achieving the microbiological stabilization objective, while Lachancea thermotolerans produces lactic acid in order not to reduce and even increase the acidity of wines produced from low acidity musts. This technique reduces the risks inherent to the malolactic fermentation process when performed in warm regions. The result is more fruity wines that contain less acetic acid and biogenic amines than the traditional controls that have undergone the classical malolactic fermentation.

An improved and validated sample cleanup method for analysis of ethyl carbamate in Chinese liquor

Ethyl carbamate (EC) is a potential human carcinogen widely existing in fermented foods and alcoholic beverages. The solid-phase extraction (SPE) coupled to gas chromatography mass spectrometry is a widely-used method to determine EC levels, but the accuracy varies with sample matrix and the effects of operation parameters are rarely examined. In this study, the influence factors involved in EC determination were investigated using Chinese liquor as sample matrix, and the improved method was further applied. Three types of SPE columns, including diatomite, Florisil, and primary-secondary amine, were compared in extraction efficiency, and the diatomite column exhibited the highest extraction efficiency. The optimal volumes of elution solvents with diatomite column were 15 mL for 3-mL samples solution loaded. In addition, the alcoholic strength for EC determination should be diluted below 20% (v/v) to avoid the enhancement of matrix-induced chromatographic response. Moreover, the pH neutralization could help improve EC recovery and peak resolution, reducing interfering effects. Based on these results, the improved method showed that the limit of detection, the limit of quantification, and average recoveries were 1.10 μg/L, 3.65 μg/L, and 93.06%, respectively. To further elucidate the underlying factors related to EC accumulation, partial least square regression analysis was conducted, and the results suggested that EC levels had the closest relationship with alcoholic strength among the remaining precursors.

The arginine deiminase pathway of koji bacteria is involved in ethyl carbamate precursor production in soy sauce

Ethyl carbamate (EC) is a group 2A carcinogen generated from a few precursors in many fermented foods and alcoholic beverages. Citrulline, urea, carbamoyl phosphate, and ethanol are common precursors detected in fermented foods. In this study, citrulline was proved to be the main EC precursor in soy sauce, which was found to be accumulated in moromi mash period and correlated with the utilization of arginine by koji bacteria. Six koji isolates belonging to three genera were identified to be able to accumulate citrulline via the arginine deiminase (ADI) pathway. Among these strains, only Pediococcus acidilactici retained high activities in synthesis and accumulation of citrulline in the presence of high concentration of sodium chloride. These results suggested that P. acidilactici is responsible for the accumulation of citrulline, one of the EC precursors, in the process of soy sauce fermentation.

Immunosuppressive effects of Pteridium aquilinum enhance susceptibility to urethane-induced lung carcinogenesis

Pteridium aquilinum (bracken fern), one of the most important toxic plants in the world, contains the toxic norsequiterpene ptaquiloside that induces cancers in humans and farm animals. Previous studies in the laboratory demonstrated immunotoxic effects produced by ptaquiloside, which are characterized by suppression of natural killer (NK) cell activity (i.e. cytotoxicity and interferon [IFN]-γ production). However, it is unknown whether these immunosuppressive effects could contribute to carcinogenesis in situ in general because of the important function of NK cells in innate killing of tumor cells. This study assessed the impact of P. aquilinum-induced immunosuppression on urethane-induced lung cancer in C57BL/6 mice. Adult mice were treated with an extract of P. aquilinum (30 g/kg/day) by gavage once daily for 14 days, followed by gavage (5 days/week) during an 11-week period that was accompanied by treatment with urethane (1 g/kg) via once-weekly intraperitoneal injection; 20 weeks after the end of the treatment period, all lungs were evaluated. The results indicated there was a significant increase in lung nodule number as well as in multiplicity of lesions in mice treated with both P. aquilinum and urethane (PU group) compared to values in mice treated only with the urethane (U group). In addition, histologic evaluation revealed a 76% increase in the rate of lung adenomas and a 41% increase in rate of bronchiolization of alveoli in the mice from the PU group compared to levels seen in mice within the U group. Taken together, the results here show for the first time that immunosuppressive effects of P. aquilinum could increase the risk of cancer formation in exposed hosts.

Nitrogen regulation involved in the accumulation of urea in Saccharomyces cerevisiae

Rice wine is a popular traditional alcoholic drink with a long history in China. However, the presence of the potential carcinogen ethyl carbamate (EC) raises a series of food safety concerns. Although the metabolic pathway of urea (the major precusor of EC) has been characterized in Saccharomyces cerevisiae, the regulation of urea accumulation remains unclear, making the efficient elimination of urea difficult. To demonstrate the regulatory mechanisms governing urea accumulation, three key nitrogen sources that can inhibit urea utilization for a commercial S. cerevisiae strain were identified. In addition, regulators of nitrogen catabolite repression (NCR) and target of rapamycin (TOR) pathways were identified as being involved in urea accumulation by real-time quantitative PCR. Based on these results, preferred nitrogen sources were found to repress urea utilization by converting them to glutamine or glutamate. Moreover, the results indicated that the manner of urea metabolism regulation was different for two positive regulators involved in NCR; Gln3p can be retained in the cytoplasm by glutamine, while Gat1p can be retained by glutamine and glutamate. Furthermore, this was confirmed by fluorescence location detection. These new findings provide new targets for eliminating EC and other harmful nitrogen-containing compounds in fermented foods.

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.