Detection of arc genes related with the ethyl carbamate precursors in wine lactic acid bacteria

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.

A new and efficient method for producing food ingredients high in l-ornithine using unused parts of white cabbage (Brassica oleracea var. capitata)

A surplus of unused parts of vegetables (e.g., white cabbage [cabbage] cores and outer leaves) is generated daily by factories of fresh-cut vegetables. These parts are difficult to effectively utilize and are often discarded as biodegradable industrial waste. This study aimed to develop an efficient method for producing l-ornithine from cabbage residues. First, we added protease (Sumizyme FP) to the cores and outer leaves of sterile cabbages. After 8 days, the amount of l-arginine released was approximately fivefold the amount in the initial content. As l-arginine is a precursor of l-ornithine, the addition of protease combined with Pediococcus pentosaceus produced l-ornithine. However, the rapid lactic acid fermentation suppressed the metabolism of l-arginine to l-ornithine, which we overcame by adjusting the pH by adding eggshell. The anaerobic fermentation of the cores and outer leaves of sterile cabbages with 5% eggshell for 8 days produced 184 ± 2 μmol of l-ornithine/100 g cabbage. PRACTICAL APPLICATIONS: This level of l-ornithine production is higher than that observed in freshwater clams (81-116 μmol/100 g), which are considered to be high in l-ornithine. This method can be applied to the production of inexpensive and safe l-ornithine-containing food materials derived from vegetables. Furthermore, ingestions of vegetables fermented by this method would provide a variety of health benefits of l-ornithine. The widespread adoption of this method will not only reduce the amount of waste generated daily from fresh-cut vegetable factories, but will also enable upcycling as a higher value-added food material.

Lactic Acid Bacteria in Wine: Technological Advances and Evaluation of Their Functional Role

Currently, the main role of Lactic Acid Bacteria (LAB) in wine is to conduct the malolactic fermentation (MLF). This process can increase wine aroma and mouthfeel, improve microbial stability and reduce the acidity of wine. A growing number of studies support the appreciation that LAB can also significantly, positively and negatively, contribute to the sensorial profile of wine through many different enzymatic pathways. This is achieved either through the synthesis of compounds such as diacetyl and esters or by liberating bound aroma compounds such as glycoside-bound primary aromas and volatile thiols which are odorless in their bound form. LAB can also liberate hydroxycinnamic acids from their tartaric esters and have the potential to break down anthocyanin glucosides, thus impacting wine color. LAB can also produce enzymes with the potential to help in the winemaking process and contribute to stabilizing the final product. For example, LAB exhibit peptidolytic and proteolytic activity that could break down the proteins causing wine haze, potentially reducing the need for bentonite addition. Other potential contributions include pectinolytic activity, which could aid juice clarification and the ability to break down acetaldehyde, even when bound to SO2, reducing the need for SO2 additions during winemaking. Considering all these findings, this review summarizes the novel enzymatic activities of LAB that positively or negatively affect the quality of wine. Inoculation strategies, LAB improvement strategies, their potential to be used as targeted additions, and technological advances involving their use in wine are highlighted along with suggestions for future research.

Inhibition of ethyl carbamate accumulation in soy sauce by adding quercetin and ornithine during thermal process

Ethyl carbamate (EC), a genotoxic and carcinogenic compound in soy sauce accumulated during thermal processes, has raised public health concern for its multipoint potential carcinogenic risk to human. In this work, based on the analysis of EC accumulation during thermal processes of soy sauce, ornithine and quercetin were added before thermal processes to reduce EC accumulation. A reduction rate of 23.7-63.8% in simulated solution was founded. Kinetic studies indicated that ornithine was a byproduct of alcoholysis reaction when EC formed, while quercetin could compete with the precursor ethanol and react with carbamyl compounds, which therefore preventedEC accumulation. A maximum of 47.2% decrease of EC in soy sauce was achieved, and no remarkable changes in volatile compounds profile and color of soy sauce were found. In conclusion, the addition of quercetin and ornithine before thermal processes may be preferable for the controlling of EC content in soy sauce.

Impact of pH on succession of sourdough lactic acid bacteria communities and their fermentation properties

Sourdough, a traditional fermented dough, is made via natural fermentation by lactic acid bacteria (LAB). Its pH changes from near neutral to acid during the subculture process. However, the product quality of subcultured sourdough depends on the unpredictable succession of LAB communities, the influential factors of which are still unclear. To elucidate one end of the LAB community succession mechanism, we evaluated the effect of pH by designing four subculture experiments using a model medium adjusted to pH 6.7, 5.5, and 4.5, as well as a natural sourdough subculture. All experiments began by inoculating a sourdough LAB mixture, and both bacterial successions and fermentative properties were monitored until ten subculture steps. In media subcultures, lactic acid production was higher in higher pH media. Three LAB genera, Weissella, Pediococcus, and Lactobacillus, each represented by one operational taxonomic unit (OTU), were successively detected in all subcultures. In later steps with lower pH media, an OTU closely related to Lactobacillus brevis dominated, replacing an OTU closely related to the Weissella cibaria-confusa group that was more dominant than the L. brevis OTU in the near-neutral pH medium. In the sourdough subculture, the three genera were also detected, while Lactobacillus was dominant in earlier steps due to the emergence of an OTU closely related to Lactobacillus sanfranciscensis. These results suggest that a lower pH is favorable for the sequence of sourdough bacterial community evolution finalizing with Lactobacillus domination. Further research is needed to elucidate additional factors other than pH that influence the pattern of LAB community shift.

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.

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.

Next-generation sequencing approaches for improvement of lactic acid bacteria-fermented plant-based beverages

Plant-based beverages and milk alternatives produced from cereals and legumes have grown in popularity in recent years due to a range of consumer concerns over dairy products. These plant-based products can often have undesirable physiochemical properties related to flavour, texture, and nutrient availability and/or deficiencies. Lactic acid bacteria (LAB) fermentation offers potential remediation for many of these issues, and allows consumers to retain their perception of the resultant products as natural and additive-free. Using next-generation sequencing (NGS) or omics approaches to characterize LAB isolates to find those that will improve properties of plant-based beverages is the most direct way to product improvement. Although NGS/omics approaches have been extensively used for selection of LAB for use in the dairy industry, a comparable effort has not occurred for selecting LAB for fermenting plant raw substrates, save those used in producing wine and certain types of beer. Here we review the few and recent applications of NGS/omics to profile and improve LAB fermentation of various plant-based substrates for beverage production. We also identify specific issues in the production of various LAB fermented plant-based beverages that such NGS/omics applications have the power to resolve.

Arginine deiminase pathway genes and arginine degradation variability in Oenococcus oeni strains

Trace amounts of the carcinogenic ethyl carbamate can appear in wine as a result of a reaction between ethanol and citrulline, which is produced from arginine degradation by some bacteria used in winemaking. In this study, arginine deiminase (ADI) pathway genes were evaluated in 44 Oenococcus oeni strains from wines originating from several locations in order to establish the relationship between the ability of a strain to degrade arginine and the presence of related genes. To detect the presence of arc genes of the ADI pathway in O. oeni, pairs of primers were designed to amplify arcA, arcB, arcC and arcD1 sequences. All strains contained these four genes. The same primers were used to confirm the organization of these genes in an arcABCD1 operon. Nevertheless, considerable variability in the ability to degrade arginine among these O. oeni strains was observed. Therefore, despite the presence of the arc genes in all strains, the expression patterns of individual genes must be strain dependent and influenced by the different wine conditions. Additionally, the presence of arc genes was also determined in the 57 sequenced strains of O. oeni available in GenBank, and the complete operon was found in 83% of strains derived from wine. The other strains were found to lack the arcB, arcC and arcD genes, but all contained sequences homologous to arcA, and some of them had also ADI activity.

Efficient synthesis of readily water-soluble sulfonic Acid carbamates

A series of various readily water-soluble carbamates were synthesized with good yields. These compounds are useful chemical tracers for assessing the cooling progress in a georeservoir during geothermal power plant operation. Acylation of primary amines was carried out as well as using a solution of sodium bicarbonate and without the presence of salt. Products were characterized by ¹H-NMR and ¹³C-NMR. Purity was confirmed through elemental analysis.

Implications of new research and technologies for malolactic fermentation in wine

The initial conversion of grape must to wine is an alcoholic fermentation (AF) largely carried out by one or more strains of yeast, typically Saccharomyces cerevisiae. After the AF, a secondary or malolactic fermentation (MLF) which is carried out by lactic acid bacteria (LAB) is often undertaken. The MLF involves the bioconversion of malic acid to lactic acid and carbon dioxide. The ability to metabolise L-malic acid is strain specific, and both individual Oenococcus oeni strains and other LAB strains vary in their ability to efficiently carry out MLF. Aside from impacts on acidity, LAB can also metabolise other precursors present in wine during fermentation and, therefore, alter the chemical composition of the wine resulting in an increased complexity of wine aroma and flavour. Recent research has focused on three main areas: enzymatic changes during MLF, safety of the final product and mechanisms of stress resistance. This review summarises the latest research and technological advances in the rapidly evolving study of MLF and investigates the directions that future research may take.

The use of nucleosides and arginine as alternative energy sources by coagulase-negative staphylococci in view of meat fermentation

The ability of coagulase-negative staphylococci (CNS) to use alternative energy sources in meat may partially explain their occurrence in fermented meats. Of 61 CNS strains tested, all metabolized adenosine and inosine in a meat simulation medium (MSM). The ability to catabolize arginine via the arginine deiminase (ADI) pathway varied between strains. All tested strains of Staphylococcus carnosus and Staphylococcus epidermidis possessed an arcA gene and showed ADI activity, whereas other species, such as Staphylococcus equorum and Staphylococcus succinus, did not. Arginine catabolic mobile elements (ACME), as in the positive control S. epidermidis ATCC 12228, were uncommon and only found in Staphylococcus xylosus 3PA6 (sausage isolate) and Staphylococcus chromogenes G222 (teat apex isolate). Monoculture experiments were performed in MSM with S. carnosus 833 and SS3-4, S. xylosus G211, and S. epidermidis ATCC 12228 and 2S7-4. At all pH values tested (5.3, 5.8, and 6.5), the strains of S. carnosus catabolized arginine faster than the strains of S. xylosus and S. epidermidis. Only at pH 6.5 could a low ADI activity be found for S. xylosus G211. Increased ADI activity occurred in the case of the ACME-positive S. epidermidis ATCC 12228, when compared to the ACME-negative S. epidermidis 2S7-4.

Effect of ethanol and low pH on citrulline and ornithine excretion and arc gene expression by strains of Lactobacillus brevis and Pediococcus pentosaceus

The accumulation of citrulline and ornithine in wine or beer as a result of the arginine catabolism of some lactic acid bacteria (LAB) species increases the risk of ethyl carbamate and putrescine formation, respectively. Several LAB species, which are found as spoilage bacteria in alcoholic beverages, have been reported to be arginine degrading. This study evaluates the effect of ethanol content and low pH on the excretion of citrulline and ornithine by two strains belonging to the potential contaminant species Lactobacillus brevis and Pediococcus pentosaceus. In the conditions that most affected cell viability, arginine consumption per cell increased noticeably, indicating that arginine utilization may be a stress responsive mechanism. L. brevis showed a higher accumulation of ornithine in the media than P. pentosaceus. In the presence of ethanol, a higher expression of the arcC gene was found in P. pentosaceus, which resulted in a lower excretion of citrulline and ornithine than in L. brevis. This suggests that L. brevis is more likely to produce these amino acids, which are precursors of ethyl carbamate and putrescine.

Biogenic amines and ethyl carbamate in primitivo wine: survey of their concentrations in commercial products and relationship with the use of malolactic starter

This research was conducted to determine the biogenic amine (BA) and ethyl carbamate (EC) concentrations in commercial Primitivo wine samples and the influence of the use of malolactic starter culture on concentrations of these potentially hazardous compounds in this wine. One hundred sixty bottles of wine from eight producers in the Apulia region of southern Italy were purchased at retail and analyzed. The most common BAs were histamine, 2-phenylethylamine, tyramine, cadaverine, putrescine, spermine, and spermidine. Putrescine (derived from ornithine) was the most abundant BA in all commercial Primitivo wines (5.41 to 9.51 mg/liter), 2-phenylethylamine was detected in only two commercial wines (at less than 2.12 mg/liter), and histamine was found at concentrations of 1.49 to 16.34 mg/liter. The concentration of EC in commercial Primitivo wine was 6.81 to 15.62 ppb, which is not considered dangerous for human health. Malolactic fermentation (MLF) affected the concentrations of BAs and EC differently. For EC, no significant differences were detected between samples of wine produced by spontaneous fermentation and wine that was inoculated malolactic starter. Mean EC concentrations were 12 and 14 ppb in two batches tested (always 18 ppb or less), regardless of whether the malolactic starter was added. Although present at trace levels in wine before the MLF, histamine accumulated during the MLF process, regardless of whether the malolactic starter was added. However, the increase in histamine was higher in wines without the malolactic starter. The concentrations of putrescine and cadaverine increased after MLF, especially in the wine that spontaneously fermented. The use of a selected malolactic starter resulted in reductions in BA concentrations in wine produced by this guided MLF compared with wine produced by spontaneous MLF.

Influence of phenolic compounds on the growth and arginine deiminase system in a wine lactic acid bacterium

The influence of seven phenolic compounds, normally present in wine, on the growth and arginine deiminase system (ADI) of Lactobacillus hilgardii X₁B, a wine lactic acid bacterium, was established. This system provides energy for bacterial growth and produces citrulline that reacts with ethanol forming the carcinogen ethyl carbamate (EC), found in some wines. The influence of phenolic compounds on bacterial growth was compound dependent. Growth and final pH values increased in presence of arginine. Arginine consumption decreased in presence of protocatechuic and gallic acids (31 and 17%, respectively) and increased in presence of quercetin, rutin, catechin and the caffeic and vanillic phenolic acids (between 10 and 13%, respectively). ADI enzyme activities varied in presence of phenolic compounds. Rutin, quercetin and caffeic and vanillic acids stimulated the enzyme arginine deiminase about 37–40%. Amounts of 200 mg/L gallic and protocatechuic acids inhibited the arginine deiminase enzyme between 53 and 100%, respectively. Ornithine transcarbamylase activity was not modified at all concentrations of phenolic compounds. As gallic and protocatechuic acids inhibited the arginine deiminase enzyme that produces citrulline, precursor of EC, these results are important considering the formation of toxic compounds.

Identification and characterization of Lactobacillus florum strains isolated from South African grape and wine samples

A total of 213 strains of lactic acid bacteria were examined in this study. Among these, 30 strains previously isolated from South African grape and wine samples remained unidentified. The identification of these isolates was performed by BLAST and phylogenetic analyses of 16S rDNA gene sequences, which indicated that the isolates belonged to Lactobacillus florum. In this work, we also designed a discriminative species-specific primer FLOR targeting the 16S rDNA gene of Lb. florum. The validity and specificity of this primer was confirmed. Of particular interest in this study was to further evaluate the identified strains for the presence of genes encoding enzymes of oenological relevance. Reference strains included three flower-associated Lb. florum (F9-1(T), F9-2 and F17) and two Lactobacillus lindneri (AWRI B530 and DSM 20691) strains. Lb. lindneri strains were incorporated as being the closest relatives of Lb. florum. PCR detection results revealed that all Lb. florum strains and Lb. lindneri AWRI B530 (grape isolate) possessed the majority of the tested genes relative to DSM 20691 (beer isolate); these enzyme-encoding genes included malolactic enzyme, peptidases (PepC, PepI, PepN), citrate lyase (α- and β-subunits), phenolic acid decarboxylase and arginine deiminase pathway enzymes (arginine deiminase and ornithine transcarbamylase). Sequence verification of PCR-generated fragments was performed by sequencing. The sequence data were used to construct the phylogenetic trees, which indicated that our Lb. florum isolates cluster with other Lb. florum strains of flower origin but rather distinct from other LAB species, with Lb. lindneri being the next closest species.