Absence Of Yeast Research Articles

Use of reconstituted kefir consortia to determine the impact of microbial composition on kefir metabolite profiles

Kefir is fermented traditionally with kefir grains, but commercial kefir production often relies on fermentation with planktonic cultures. Kefir has been associated with many health benefits, however, the utilization of kefir grains to facilitate large industrial production of kefir is challenging and makes to difficult to ensure consistent product quality and consistency. Notably, the microbial composition of kefir fermentations has been shown to impact kefir associated health benefits. This study aimed to compare volatile compounds, organic acids, and sugar composition of kefir produced through a traditional grain fermentation and through a reconstituted kefir consortium fermentation. Additionally, the impact of two key microbial communities on metabolite production in kefir was assessed using two modified versions of the consortium, with either yeasts or lactobacilli removed. We hypothesized that the complete kefir consortium would closely resemble traditional kefir, while the consortia without yeasts or lactobacilli would differ significantly from both traditional kefir and the complete consortium fermentation. Kefir fermentations were examined after 12 and 18 h using two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC-TOFMS) to identify volatile compounds and high performance liquid chromatography (HPLC) to identify organic acid and sugar composition. The traditional kefir differed significantly from the kefir consortium fermentation with the traditional kefir having 15–20 log2(fold change) higher levels of esters and the consortium fermented kefir having between 1 and 3 log2(fold change) higher organic acids including lactate and acetate. The use of a version of kefir consortium that lacked lactobacilli resulted in between 2 and 20 log2(fold change) lower levels of organic acids, ethanol, and butanoic acid ethyl ester, while the absence of yeast from the consortium resulted in minimal change. In summary, the kefir consortium fermentation is significantly different from traditional grain fermented kefir with respect to the profile of metabolites present, and seems to be driven by lactobacilli, as evidenced by the significant decrease in multiple metabolites when the lactobacilli were removed from the fermentation and minimal differences observed upon the removal of yeast.

Physicochemical, Microbiological and Sensory Characteristics of White Brined Cheese Ripened and Preserved in Large-Capacity Stainless Steel Tanks.

The objective of the present study was to investigate the effect of ripening and preservation containers on the physico-chemical, microbiological, and textural characteristics, and volatile profile of white cheese. White cheeses were manufactured on an industrial scale using large-capacity stainless steel tanks (SST) of 500 kg, and the respective control samples in tin containers (TC) of 17 kg. No significant differences (p > 0.05) in fat in dry matter and total protein content were observed at 60 days of ripening between the TC and SST cheeses. After 60 days, of ripening, the moisture of the cheeses in SST and TC did not show significant statistical differences (p > 0.05). No significant differences (p > 0.05) were observed between the TC and SST cheeses in the mineral concentration (Ca, Mg, K, and Na) and textural characteristics. Similar results of pH and bacterial counts, as well as absence of yeasts and molds, were observed during ripening and preservation time in both groups of cheeses. Furthermore, proteolysis was not affected statistically significantly (p > 0.05). A moderately increased rate of ripening for the cheeses in TC was observed up to 90 days but, at 180 days, proteolysis was similar in both groups of cheeses. Regarding the SFA, MUFA, and PUFA content, no significant differences (p > 0.05) were observed between the TC and SST cheeses. A total of 94 volatile compounds were identified in the volatile fraction of both the SST and TC cheeses. Organic acids and alcohols were the most abundant classes of volatile compounds that were identified. The flavor and texture scores in the TC and SST cheeses were similar (p > 0.05). Overall, the TC and SST cheeses did not show any significant statistical difference in any of the analyzed parameters.

Investigation of Geraniol Biotransformation by Commercial Saccharomyces Yeast Strains by Two Headspace Techniques: Solid-Phase Microextraction Gas Chromatography/Mass Spectrometry (SPME-GC/MS) and Proton Transfer Reaction-Time of Flight-Mass Spectrometry (PTR-ToF-MS)

Hop-derived volatile organic compounds (VOCs) and their transformation products significantly impact beer flavour and aroma. Geraniol, a key monoterpene alcohol in hops, has been reported to undergo yeast-modulated biotransformation into various terpenoids during fermentation, which impacts the citrus and floral aromas of the finished beer. This study monitored the evolution of geraniol and its transformation products throughout fermentation to provide insight into differences as a function of yeast species and strain. The headspace concentration of VOCs produced during fermentation in model wort was measured using Solid-Phase Microextraction Gas Chromatography/Mass Spectrometry (SPME-GC/MS) and Proton Transfer Reaction-Time of Flight-Mass Spectrometry (PTR-ToF-MS). In the absence of yeast, only geraniol was detected, and no terpenoid compounds were detected in geraniol-free ferments. During fermentation, the depletion of geraniol was closely followed by the detection of citronellol, citronellyl acetate and geranyl acetate. The concentration of the products and formation behaviour was yeast strain dependent. SPME-GC/MS provided confidence in compound identification. PTR-ToF-MS allowed online monitoring of these transformation products, showing when formation differed between Saccharomyces cerevisiae and Saccharomyces pastorianus yeasts. A better understanding of the ability of different yeast to biotransform hop terpenes will help brewers predict, control, and optimize the aroma of the finished beer.

Microbiological quality and sensory perception of Sclerocarya birrea (A. Rich.) Hochst. Pulp juice in Niger

The Sclerocarya birrea tree is a widespread and little-studied multipurpose forest species in Niger. The objective of this study was to evaluate the microbiological quality and sensory perception of fruit pulp juices from two different regions. The results showed that the germs of alteration range from absence to 22 CFU/g for total mesophilic aerobic flora, from 01 to 08 CFU/g for total coliforms, the absence of yeasts and molds for 4 samples, the presence of yeasts at the level of 3 samples, varying from 02 to 23 CFU/g, and the absence of sulfite-reducing anaerobic germs for all sites. The presence of pathogenic germs in E. coli from 03 to 08 UCF/g was noted, but no salmonella was found, and staphylococci were found in at least two samples. There was no effect produced by the descriptors on the acid-sugar and acid-taste balance (P > 0.05), and the judges have different rating scales. The correlation analysis shows that there is an agreement among some panel members. The hedonic rating shows that two samples out of six did not obtain a good mean from consumers and global appreciation for the other four samples. It appears that good hygiene and processing practices must be reviewed in juice processing. In addition, the fruits of S. birrea are very acidic but also sweet, which requires the search for adequate methods of preservation to improve the taste qualities of its juice.

New Insights into the Origin of Volatile Sulfur Compounds during Wine Fermentation and Their Evolution during Aging

Volatile sulfur compounds (VSCs) are associated with unpleasant reductive aromas and are responsible for an important reduction in wine quality, causing major economic losses. Understanding the origin of these compounds in wine remains a challenge, as their formation and further evolution during winemaking can involve both chemical and biological reactions. Comparing the VSCs profile (i) of fermenting synthetic grape juices supplemented with a selected VSC (eight compounds tested) and incubated in presence or absence of yeast, and (ii) during storage of wines under an accelerated aging procedure, allowed us to elucidate the chemical and metabolic connections between VSCs during fermentation and aging. Yeast metabolism, through the Ehrlich pathway and acetylation reactions, makes an important contribution to the formation of compounds such as methionol, 3-methylthiopropionate, 3-methylthiopropylacetate, 3-mercaptopropanol, 2-mercaptoethanol and thioesters. By contrast, chemical reactions are responsible for interconversions between thiols and disulfides, the formation of thiols from thioesters or, more surprisingly, the formation of ethylthiopropanol from methionol during fermentation. During aging, variations in heavy VSC concentrations, such as an increase in 3-methylthiopropylacetate and a decrease in ethyl-3-methylthiopropionate formation, were evidenced. Overall, this study highlights that it is essential to consider both yeast metabolism and the high chemical reactivity of VSCs to understand their formation and evolution during winemaking.

Replacement of meat by mycoproteins in cooked sausages: Effects on oxidative stability, texture, and color

Processed meat is one of the most consumed products worldwide. Naturally, production of proteins with animal origins includes limitations such as costs, energy, time, and environmental problems. Thus, replacement of meats by alternative biomaterials such as mycoproteins can be promising. Mycoproteins with hyphal morphologies, including branches and lengths, have close structures to meat and can be a potential alternative for meat products. Therefore, the major objectives of this study included complete replacement of sausage meats by mycoproteins and comparing characteristics of the novel formula with those of meat. In general, physicochemical, microbial, nutritional, and mechanical characteristics of the formulas were assessed. Results showed that the mycoprotein substitution improved the nutritional and health effects due to the higher valuable protein and lower lipid contents. Besides, it had a high content of essential amino acid and unsaturated fatty acid, compared to meat sausage. Absence of yeasts, molds, Salmonella spp., Eshrichia (E.)coli, and Staphiloccocus (S.)aureus verified the effectiveness of the heat treatment and also the effectiveness of the hygienic procedures in both samples. With regard to phycicochemical properties, more contents of moisture and lipids in sausages containing mycoprotein were linked to further water binding capacity (WBC) (P < 0.05) and oil binding capacity (OBC) in them, compared to beef samples. Besides, the mycoprotein sample had lower (P < 0.05) values of carbohydrates, ash, and pH, compared to the beef sample. In contrast, beef sausages had better textural characteristics, such as hardness, cohesiveness, gumminess, and springiness indexes, compared to mycoprotein sausages. Higher water and OBC values of the mycoproteins led to the filling of the protein interstitial spaces as well as decreasing of the textural attributes. Thus, it resulted in the use of less oil and water in mycoprotein formulations. In conclusion, mycoproteins can be addressed as appropriate replacements for meats in sausages.

Novel scaffold based graphene oxide doped electrospun iota carrageenan/polyvinyl alcohol for wound healing and pathogen reduction: in-vitro and in-vivo study

Wound healing is a complicated multicellular process that involves several kinds of cells including macrophages, fibroblasts, endothelial cells, keratinocytes and platelets that are leading to their differentiation towards an anti-inflammatory response for producing several chemokines, cytokine and growth factors. In this study, electrospun nanofiber scaffold named (MNS) is composed of polyvinyl alcohol (PVA)/iota carrageenan (IC) and doped with partially reduced graphene oxide (prGO) that is successfully synthesized for wound healing and skin repair. The fabricated MNS was tested in case of infection and un-infection with E. coli and Staphylococcus and in both of the presence and in the absence of yeast as a natural nutritional supplement. Numerous biochemical parameters including total protein, albumin, urea and LDH, and hematological parameters were evaluated. Results revealed that the MNS was proved to be effective on most of the measured parameters and had exhibited efficient antibacterial inhibition activity. Whereas it can be used as an effective antimicrobial agent in wound healing, however, histopathological findings confirmed that the MNS caused re-epithelialization and the presence of yeast induced hair follicles growth and subsequently it may be used to hide formed head wound scar.

Physicochemical, Sensory, and Microbial Characteristics of Kindirmou and Pendidam, Two Traditional Fermented Milks of Adamawa - Cameroon, as Affected by the Fermentation Vessels

Recent data show that the containers traditionally used for fermentation, due to their nature, exchange with the fermented product, the consequence being a modification of the physico-chemical, microbiological and organoleptic properties of these products. The objective of this work is to study the influence of the fermentation vessel on the sensory, physicochemical, and microbial properties of kindirmou and pendidam, two traditional fermented milks from Adamawa - Cameroon. To this end, a descriptive test was used to generate the sensory properties of fermented milks in different containers, followed by biochemical (pH, titratable acidity, protein, sugar content, and total phenolic compounds) and microbiological analyses (total aerobic mesophilic flora, coliforms, lactic acid bacteria, yeasts and molds). Regarding sensory evaluation, samples of kindirmou and pendidam fermented in calabashes have a higher general acceptability than those fermented in plastic buckets and enamel plates. The total mesophilic flora and total coliforms were higher than the norm (≥ 6log10) for kindirmou and pendidam regardless of the fermentation vessel. The absence of yeasts and molds is noted in the samples of kindirmou, while they are found at very high levels in the samples of pendidam fermented in the calabash and in the enamel plates ((≥ 6log10). Fecal coliforms are absent in samples of kindirmou and pendidam fermented in the calabash, while they are found in samples fermented in plastic buckets and enamel plates. On the physicochemical level, the results obtained showed that the kindirmou fermented in the calabash had the highest soluble protein content (1.47 ± 0.04 g / 100 mL of milk) than those fermented in plastic bucket and enamel plates. The phenolic compounds are present only in the samples of milk fermented in the calabash and the average contents are 93.41 ± 3.04 mg / 100 mL of milk for kindirmou and 111.20 ± 2.01 mg / 100 mL for pendidam.
 To conclude, kindirmou and pendidam fermented in calabashes exhibit the best sensory and physicochemical characteristics, and are rich in bioactive compounds than those fermented in plastic buckets and enamel plates.

DEVELOPMENT OF NEW FUNCTIONAL SYNBIOTIC DAIRY BEVERAGE BASED ON THE BASE OF WHEY

Over the past decade, consumers' approach to healthy nutrition has changed dramatically, and today, particular importance is attached to increasing the life expectancy of the population through the consumption of healthy foods. The general deterioration in population health, a decrease in resistance to infections, and the widespread spread drug resistance of pathogens require the development of healthy products preventing pathogenic microorganisms’ growth and increasing the body's defense. Dairy products have a significant place in the functional food market, and functional milk-based drinks are a growing segment of this sector. An association of lactic acid bacteria Lactobacillus paracasei 4m-2b, Lactobacillus fermentum A15, acetic acid bacteria Acetobacter fabarium 4-4M, and lactose-fermenting yeast Kluyveromyces marxianus 4МА, which has antagonistic activity against fungal and bacterial cultures from the genera Escherichia, Salmonella, Sarcina, Mycobacterium, Candida, Fusarium, Penicillium was used as a starter for the beverage. Wheat bran containing significant amounts of insoluble dietary fiber was used as a prebiotic additive. To improve the sensory properties, biological and nutritional values, ​​and to expand the spectrum of antagonistic activity of the starter microorganisms, various plant supplements were used. Variants of fermented milk drinks with the addition of yeast and without yeast were obtained. A higher antagonistic activity of beverage variants not including Kluyveromyces marxianus 4MA in the starter culture was shown against Salmonella enterica Serotype Dublin. However, suppression of Candida albicans B514 was most effective in the absence of yeast in the starter culture. The best variant of a whey-based synbiotic beverage with wheat bran and addition of raspberries, millet and mare's milk has been selected. The resulting fermented beverage was characterized by high sensory characteristics and a wide spectrum of bacterial and fungal test cultures inhibition. Key words: whey, functional symbiotic beverage, antibacterial activity, antifungal activity, plant supplements, mare’s milk, probiotic, prebiotic.

Impact of Copper Fungicide Use in Hop Production on the Total Metal Content and Stability of Wort and Dry-Hopped Beer

Transition metals, including copper, iron, and manganese, are known to catalyze the generation of reactive oxygen species (ROS) in beer leading to reduced product stability. Metals in beer are generally derived from raw ingredients. The present study aims to evaluate the impact of brewing and dry-hopping using hops treated with copper-based fungicides (CBFs) on the final transition metal content of model buffer solutions and pilot-scale systems of wort and beer. Copper levels in model wort and beer solutions were elevated (105.6% and 230.4% increase, respectively) when CBF-treated hops were used. In laboratory-prepared wort, elevated copper concentrations were not observed when CBF-treated hops were used for boiling. Dry hopping of beer using CBF-treated hops led to significant increases in total copper content (ca. 75 µg/kg vs. ca. 40–50 µg/kg in the control-hopped beer) when yeast was absent from the treated beer, but not when yeast was present. It was observed that manganese levels were significantly elevated in all hopped beers (ca. 495–550 µg/kg vs. 90–125 µg/kg in the unhopped control), regardless of hop treatment. A hop varietal thiol, 4-Mercapto-4-methylpentan-2-one, was spiked into treated beers, and the rate of oxidative loss was monitored during aging. Rates of thiol loss in treated beer samples did not differ across CBF treatments but were significantly lower in unhopped controls in the absence of yeast (p < 0.0001) and correlated significantly with total manganese content of the beers (R2 = 0.4228, p = 0.0006). The rate of staling in hopped beers as measured by the rate of 1-hydroxyethyl radical generation did not differ among hop treatments, suggesting that excess copper content contributed from the hops does not negatively impact the oxidative stability of the beers. These findings suggest that brewers can use CBF-treated hops without any negative implications for the shelf stability of their beers and do not contraindicate the use of CBF in hops production when necessary.

Association Between Vaginal Bacterial Microbiota and Vaginal Yeast Colonization.

Vaginal yeast is frequently found with Lactobacillus-dominant microbiota. The relationship between vaginal yeast and other bacteria has not been well characterized. These analyses utilized data from the Preventing Vaginal Infections trial. Relative abundance of vaginal bacteria from 16S ribosomal ribonucleic acid gene amplicon sequencing and quantities of 10 vaginal bacteria using taxon-directed polymerase chain reaction assays were compared at visits with and without detection of yeast on microscopy, culture, or both. Higher relative abundances of Megasphaera species type 1 (risk ratio [RR], 0.70; 95% confidence interval [CI], 0.52-0.95), Megasphaera species type 2 (RR, 0.81; 95% CI, 0.67-0.98), and Mageeibacillus indolicus (RR, 0.46; 95% CI, 0.25-0.83) were associated with lower risk of detecting yeast. In contrast, higher relative abundances of Bifidobacterium bifidum, Aerococcus christensenii, Lactobacillus mucosae, Streptococcus equinus/infantarius/lutentiensis, Prevotella bivia, Dialister propionicifaciens, and Lactobacillus crispatus/helveticus were associated with yeast detection. Taxon-directed assays confirmed that increasing quantities of both Megasphaera species and M indolicus were associated with lower risk of detecting yeast, whereas increasing quantities of L crispatus were associated with higher risk of detecting yeast. Despite an analysis that examined associations between multiple vaginal bacteria and the presence of yeast, only a small number of vaginal bacteria were strongly and significantly associated with the presence or absence of yeast.

Nop9 recognizes structured and single-stranded RNA elements of preribosomal RNA

Nop9 is an essential factor in the processing of preribosomal RNA. Its absence in yeast is lethal, and defects in the human ortholog are associated with breast cancer, autoimmunity, and learning/language impairment. PUF family RNA-binding proteins are best known for sequence-specific RNA recognition, and most contain eight α-helical repeats that bind to the RNA bases of single-stranded RNA. Nop9 is an unusual member of this family in that it contains eleven repeats and recognizes both RNA structure and sequence. Here we report a crystal structure of Saccharomyces cerevisiae Nop9 in complex with its target RNA within the 20S preribosomal RNA. This structure reveals that Nop9 brings together a carboxy-terminal module recognizing the 5′ single-stranded region of the RNA and a bifunctional amino-terminal module recognizing the central double-stranded stem region. We further show that the 3′ single-stranded region of the 20S target RNA adds sequence-independent binding energy to the RNA–Nop9 interaction. Both the amino- and carboxy-terminal modules retain the characteristic sequence-specific recognition of PUF proteins, but the amino-terminal module has also evolved a distinct interface, which allows Nop9 to recognize either single-stranded RNA sequences or RNAs with a combination of single-stranded and structured elements.

Comparison of uniaxial/biaxial extensional rheological properties of mixed dough with traditional rheological test results: relationship with the quality of steamed bread

SummaryThe formula and preparation of steamed bread are different from those of western bread. The extensional rheological behaviour plays a key role in the development of steamed bread dough. However, there are inadequate studies on the rheological properties of mixed dough with yeast. In this study, the relationship between properties of dough in the presence or absence of yeast was elucidated. Besides, the flour characteristics and quality of steamed bread prepared from different wheat varieties were evaluated. The uniaxial/biaxial extensional rheological properties of wheat dough were compared with traditional rheological test results. Large deformations in the extensional properties were measured by Extensograph and the Kieffer extensibility rig, while the biaxial extension was quantified using uniaxial compression. These characteristics of dough and flour correlated with each other in different ways. Correlation analysis illustrated that the uniaxial extensional rheological properties of dough with yeast better indicated the quality of the steamed bread. Moreover, the total work for breakage of the dough with yeast was the best predictor for specific volume of steamed bread. The texture‐based properties of steamed bread showed correlation with biaxial extension viscosity. The rheological tests provide useful information for evaluating wheat flour and steamed bread quality.

Evaluation De La Qualité Microbiologique Des Médicaments Traditionnels Améliorés (MTA) Vendus Dans Six Communes d’Abidjan (Côte d’Ivoire)

This study was carried out in six (6) communes of Abidjan within a period of six months (November 2016 to April 2017). This paper focuses on assessing the microbiological quality of traditional medicines produced and sold in these communes. A total of 38 samples were collected, including 19 in powder form and another 19 in liquid form. The search and enumeration of the germs was carried out according to the method based on standard procedures (AFNOR). Enumeration included total mesophilic aerobic flora, total coliforms, yeasts and molds, Staphylococcus aureus, and salmonella. The results indicate an absence of the pathogenic flora (Salmonella and S. aureus). There is also an absence of yeasts and molds in the products in liquid form. The level of contamination of the Mesophilic Total Aerobic Flora (FMAT) ranges from 1.104 to 6.7.107 CFU / ml or CFU / g and from 1.6.104 to 5.5.107 CFU / g or CFU / ml for total coliforms. In terms of microbiological quality, 39.47% of the analyzed samples had compliant. In view of these results, it is necessary to train Traditional Medicine Practitioners on Good Manufacturing Practices (GMP) methods throughout the production chain in order to market MTAs of guaranteed quality and safety

Evolution of peroxisomes illustrates symbiogenesis.

Recently, the group of McBride reported a stunning observation regarding peroxisome biogenesis: newly born peroxisomes are hybrids of mitochondrial and ER-derived pre-peroxisomes. What was stunning? Studies performed with the yeast Saccharomyces cerevisiae had convincingly shown that peroxisomes are ER-derived, without indications for mitochondrial involvement. However, the recent finding using fibroblasts dovetails nicely with a mechanism inferred to be driving the eukaryotic invention of peroxisomes: reduction of mitochondrial reactive oxygen species (ROS) generation associated with fatty acid (FA) oxidation. This not only explains the mitochondrial involvement, but also its apparent absence in yeast. The latest results allow a reconstruction of the evolution of the yeast's highly derived metabolism and its limitations as a model organism in this instance. As I review here, peroxisomes are eukaryotic inventions reflecting mutual host endosymbiont adaptations: this is predicted by symbiogenetic theory, which states that the defining eukaryotic characteristics evolved as a result of mutual adaptations of two merging prokaryotes.

High-dose fluconazole in combination with amphotericin B is more efficient than monotherapy in murine model of cryptococcosis

Cryptococcus spp., the causative agents of cryptococcosis, are responsible for deaths of hundreds of thousands of people every year worldwide. The drawbacks of available therapeutic options are aggravated by the increased resistance of yeast to the drugs, resulting in inefficient therapy. Also, the antifungal 5FC is not available in many countries. Therefore, a combination of antifungal drugs may be an interesting option, but in vitro and theoretical data point to the possible antagonism between the main antifungals used to treat cryptococcosis, i.e., fluconazole (FLC), and amphotericin B (AMB). Therefore, in vivo studies are necessary to test the above hypothesis. In this study, the efficacy of FLC and AMB at controlling C. gattii infection was evaluated in a murine model of cryptococcosis caused by C. gattii. The infected mice were treated with FLC + AMB combinations and showed a significant improvement in survival as well as reduced morbidity, reduced lung fungal burden, and the absence of yeast in the brain when FLC was used at higher doses, according to the Tukey test and principal component analysis. Altogether, these results indicate that combinatorial optimization of antifungal therapy can be an option for effective control of cryptococcosis.

Investigation of 2-Sulfanylethyl Acetate Cysteine-S-Conjugate as a Potential Precursor of Free Thiols in Beer

The compounds 2-sulfanylethyl acetate (2SEA, roasted- or burnt-like flavor) and 3-sulfanylpropyl acetate (also with roasted- or burnt-like flavor), mainly issued from the Ehrlich pathway (in this case, the catabolism by yeast of cysteine and homocysteine, leading to the formation of 2-sulfanylethan-1-ol and 2-sulfanylpropan-1-ol, which are subsequently acetylated), are found in all fresh beers, at levels strongly depending on the yeast strain used in fermentation. Yet, even in the absence of yeast, their production is still seen to occur in the bottle during the first months of storage. As for other thiols, S-cysteine adducts have been suspected to be hydrolyzed during beer aging. The commercially unavailable S-cysteine conjugate of 2SEA (Cys-2SEA, 93% purity), never described before in the literature, was synthesized by acetylation of the S-cysteine conjugate of 2-sulfanylethan-1-ol (Cys-2SEol). Cys-2SEA was solubilized in model aqueous media (pH 4.2) and in beer before aging. 2SEA was further extracted and analyzed by gas chromatography coupled to a pulsed flame photometric detector (GC-PFPD), and high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC-ESI(+)-MS/MS) allowed us to quantify the undegraded Cys-2SEA (specific m/z ions at 120, 148, and 191). Cys-2SEA was shown to be relatively stable in both media, although some beer constituents were noted as being able to slightly facilitate the chemical degradation (molar conversion into free thiol up to 0.3% at room temperature). A modified “Strecker degradation” mechanism is proposed here, explaining the release of thiols from the Schiff bases created between the cysteine adducts and beer diketones. Up to now, tests have failed to reveal evidence for the presence of Cys-2SEol and Cys-2SEA in hops by direct HPLC-ESI(+)-MS/MS analyses, although 2SEol was released from cysteine-S-conjugate extracts in the presence of apotryptophanase.

Synthesis of Macro‐Mesoporous MCM‐41 and Its Use in Methylene Blue Adsorption

AbstractMCM‐41 was synthesized in the presence of yeast cells (Saccharomyces cerevisiae). The corresponding calcined material was characterized by scanning electron microscopy, X‐ray diffraction, nitrogen sorption, and mercury porosimetry and compared to MCM‐41 silica synthesized in the absence of yeast. The material synthesized with yeast cells showed equally sized ordered mesoporous silica particles arranged around macropores. These macropores are negative replica of the yeast cells. This material has superior methylene blue adsorption properties from aqueous solution in comparison to ordinary MCM‐41.

Polyfunctional Thiols in Fresh and Aged Belgian Special Beers: Fate of Hop S-Cysteine Conjugates

Odorant polyfunctional thiols such as 4-sulfanyl-4-methylpentan-2-one, 3-sulfanylhexan-1-ol (3SHol), and 3-sulfanyl-3-methylbutan-1ol (3S3MBol) were shown to be strongly degraded in Belgian special beers after 1 year of aging. Yet, during the first 3 months, they also appeared to be synthesized in the bottle, even in the absence of yeast. Fresh filtered lager beer was spiked with nonvolatile S-cysteine conjugates of 3SHol, 3S3MBol, and 3-methylbut-2-en-1-thiol (MBT) before aging (1 to 3 months at 20°C or 5 days at 40 or 60°C). Thiol-specific para-hydroxymercuribenzoic acid extracts were analyzed by a GC-pulsed flame photometric detector, and HPLC-electrospray ionization/MS/MS was used to quantify the undegraded cysteinylated precursors. S-Cysteine conjugates were chemically degraded in the beer, releasing their corresponding thiols. The conversions were low (<1%) but could explain the trace amounts of 3SHol and 3S3MBol produced in beer during the first months of storage. On the other hand, chemical degradation of Cys-MBT in beer (although reaching up to 33%) proved not to be efficient enough to release significant amounts of the skunky off-flavor. In this case, photooxidative degradation of isohumulone most probably remains the major synthesis pathway. Complementary analyses are now needed to determine how other beer constituents, such as dicarbonyls, might participate in cysteine adduct degradation.

A S‐adenosylmethionine methyltransferase‐like domain within the essential, Fe‐S‐containing yeast protein Dre2

Yeast Dre2 is an essential Fe-S cluster-containing protein that has been implicated in cytosolic Fe-S protein biogenesis and in cell death regulation in response to oxidative stress. Its absence in yeast can be complemented by the human homologous antiapoptotic protein cytokine-induced apoptosis inhibitor 1 (also known as anamorsin), suggesting at least one common function. Using complementary techniques, we have investigated the biochemical and biophysical properties of Dre2. We show that it contains an N-terminal domain whose structure in solution consists of a stable well-structured monomer with an overall typical S-adenosylmethionine methyltransferase fold lacking two α-helices and a β-strand. The highly conserved C-terminus of Dre2, containing two Fe-S clusters, influences the flexibility of the N-terminal domain. We discuss the hypotheses that the activity of the N-terminal domain could be modulated by the redox activity of Fe-S clusters containing the C-terminus domain in vivo.