Formation Of Diacetyl Research Articles

Some enzymatic properties of lactic acid bacteria isolated from dairy products

This article presents data on the study of physiological and biochemical properties, antagonistic and enzymatic activity of lactic acid bacteria isolated from dairy products.9 types of lactic acid bacteria were studied:Lactobacillus bulgaricus GM – 08, Lactobacillus bulgaricus KZh – 01,Lactobacillus bulgaricus GS – 03, Lactococcus cremoris – 6, Lactococcus cremoris – 17, Lactococcus cremoris – 26, Lactococcus lactis – 1,Lactococcus lactis – 15, Lactococcus lactis – 23. These strains were found to have resistance to 2% and 4%-vertical NaCl concentrations, bile and phenol.In addition, the antagonistic activity of Gram-positive and Gram-negative microorganisms in relation to test cultures of Staphylococcus aureus, Salmonella dublin, Escherichia coli, Bacillus subtilis, Sarcina flava was studied.All studied lactic acid bacteria showed activity in Test cultures with different inhibition zones. The Lactococcus lactis – 23 strains showed high activity for all cultures, with an inhibition zone of 17-25 mm.Further, 5 strains were selected from these strains and their aroma-forming properties, the formation of diacetyl and ammonia from arginine, hemolytic and lecithinase activity were studied.Compositions were compiled from these strains to make yeast.The compatibility of strains of lactic acid bacteria was checked with each strain individually and with the duration of milk clotting according to organoleptic indicators compared to the duration of milk clotting.Thus, the most active clot formation was obtained by the Lactococcus lactis – 23 strainof the selected combinations.

Optimal Design Approach Applied to Headspace GC for the Monitoring of Diacetyl Concentration, Spectrophotometric Assessment of Phenolic Compounds and Antioxidant Potential in Different Fermentation Processes of Barley

The present study aimed to validate a control method on the gas chromatography system (GC) based on the experimental design strategy, to examine the changes and correlation between the fermentation process and the quality of alcoholic and non-alcoholic beer product, especially the formation of diacetyl. On the other hand, spectrophotometric methods were applied to the determination of polyphenols content and the potential antioxidant activity of beer during different fermentation processes. with this aim, three modes of barley fermentation were used, specifically classical fermentation, stopped fermentation and thermal process. The results showed that the different fermentation modes had a major impact on diacetyl production. The highest concentration was obtained using stopped fermentation 0.36 mg/L, the lowest concentration value 0.07 mg/L was detected using the thermal process. Monitoring the increase of oxygen concentration between fermentation, filtration, and filling of the final product (32, 107, 130 ppm, respectively) has a significant impact on the concentration of diacetyl. The obtained results of spectrophotometric analysis showed that the total antioxidant activity changed during beer fermentation process and demonstrate that the extend of the antioxidant activity was very much dependent on the total polyphenolic content with a higher value in Hopped wort (13.41%, 65 mg GAE 100 mL−1, 28 mg CE 100 mL−1) for antioxidant potential, total phenolic content, and total flavonoids content, respectively, whereas the lowest values was detected in Non-alcoholic beer using thermal process (7.24%, 35 mg GAE 100 mL−1, 10 mg CE 100 mL−1) for antioxidant potential, total phenolic contents, and total flavonoids contents, respectively. Based on the results achieved, we reveal the impact of the fermentation process on the nutritional value of the final product.

Nutritional and Volatile Characterisation of Milk Inoculated with Thermo-Tolerant Lactobacillus bulgaricus through Adaptive Laboratory Evolution.

In this study, thermo-tolerant strain of Lactobacillus bulgaricus (L. bulgaricus) was developed using gradual increase in temperature to induce Adaptive Laboratory Evolution (ALE). Viable colony count of 1.87 ± 0.98 log cfu/mL was achieved at 52 °C, using MRS agar supplemented with 2% lactose. Changes in bacteria morphology were discovered, from rod (control) to filament (52 °C) to cocci after frozen storage (−80 °C). When milk was inoculated with thermo-tolerant L. bulgaricus, lactic acid production was absent, leaving pH at 6.84 ± 0.13. This has caused weakening of the protein network, resulting in high whey separation and lower water-holding capacity (37.1 ± 0.35%) compared to the control (98.10 ± 0.60%). Significantly higher proteolytic activity was observed through free amino acids analysis by LC-MS. Arginine and methionine (237.24 ± 5.94 and 98.83 ± 1.78 µg/100 g, respectively) were found to be 115- and 275-fold higher than the control, contributing to changing the aroma similar to cheese. Further volatile analysis through SPME-GC-MS has confirmed significant increase in cheese-aroma volatiles compared to the control, with increase in diacetyl formation. Further work on DNA profiling, metabolomics and peptidomics will help to answer mechanisms behind the observed changes made in the study.

Kinetics of α‑dicarbonyl compounds formation in glucose-glutamic acid model of Maillard reaction.

As a potential health hazard, α‐dicarbonyl compounds have been detected in the thermally processed foods. In order to investigate the formation kinetics of α‐dicarbonyl compounds, liquid chromatography‐electrospray tandem mass spectrometry was employed to determine the content of α‐dicarbonyl compounds in glucose‐only and glucose‐glutamic acid (glucose‐Glu) thermal reaction models. The 3‐deoxyglucosone content was significantly higher than 6 α‐dicarbonyl compounds at 90–110℃, 0–6 hr in the two tested systems. The glutamic acid promoted the content accumulation of 1‐deoxyglucosone, diacetyl, methylglyoxal, and glyoxal, whereas inhibited the content of 3‐deoxyglucosone and 3,4‐dideoxyglucosone. Three‐fifths of the tested compounds content increased linearly with time increasing, but in glucose‐only system, the 1‐deoxyglucosone content increased logarithmically at 95–110℃ over reaction time. The formation of glucose (100–110℃, glucose‐only and glucose‐Glu), 5‐hydroxymethylfurfural (100–110℃, glucose‐only), 1‐deoxyglucose (105–110℃, glucose‐Glu), 3,4‐dideoxyglucosone (110℃, glucose‐Glu), glyoxal (95–110℃, glucose‐Glu) and diacetyl (90–95℃, glucose‐Glu) could be well fitted by exponential equation. Shortening the heating time and reducing heating temperature (except glyoxal in glucose‐only system) were the effective methods to decrease α‐dicarbonyl compounds content in the two tested systems. Additionally, high temperature could also reduce α‐dicarbonyl compounds content, such as 3‐deoxyglucosone (≥110℃, glucose‐only), 1‐deoxyglucosone (≥110℃, glucose‐only), glucosone (≥110℃, glucose‐only; ≥100℃, glucose‐Glu), methyloxyl (≥110℃, glucose‐only; ≥100℃, glucose‐Glu), diacetyl (≥110℃, glucose‐only), and glyoxal (≥100℃, glucose‐Glu).

Growth, survival, and metabolic activities of probiotic Lactobacillus spp. in fermented coffee brews supplemented with glucose and inactivated yeast derivatives

Amidst rising interest in non-dairy probiotic foods, and growing global coffee consumption patterns, it would be opportune to ferment coffee brews with probiotics, yet it remains unexplored. In this study, we aimed to develop a fermented coffee beverage rich in live probiotics, by supplementing nutrient-deficient coffee brews with glucose and inactivated yeast derivatives. This was followed by fermentation with single probiotic bacteria cultures (Lactobacillus rhamnosus GG, L. paracasei Lpc-37, L. plantarum 299v, and L. acidophilus NCFM), and subsequent storage at 4 and 25 °C. We demonstrated that nutrient supplementation was essential in supporting probiotic growth and survival in coffee brews, as viabilities above 7 Log CFU/mL could not be sustained longer than 2 weeks in non-supplemented coffees. In contrast, viabilities above 7 Log CFU/mL were maintained for 10 weeks by L. rhamnosus GG and L. paracasei Lpc-37 in supplemented coffees stored under refrigeration. Probiotic metabolic activities led to consumption of glucose, glutamic acid, and alanine, with simultaneous formation of lactic acid, 3-methylbutanoic acid, and diacetyl. Nevertheless, endogenous coffee volatiles, bioactive components, and antioxidant capacities were retained. Overall, we illustrate the potential functionalities of probiotic fermented coffee brews, arising from high probiotic live counts and retention of major coffee bioactive components.

Formation of Diacetyl and Other α-Dicarbonyl Compounds during the Generation of E-Vapor Product Aerosols.

Exposure to diacetyl (DA) has been linked to the respiratory condition bronchiolitis obliterans. Previous research has demonstrated that DA and other α-dicarbonyl compounds can be detected in both the e-liquids and aerosols of e-vapor products (EVPs). While some EVP manufacturers may add these compounds as flavor ingredients, the primary objective of this work was to determine the potential for the formation of α-dicarbonyl compounds during the generation of aerosols from EVPs where no DA or other α-dicarbonyl compounds are added to the e-liquid. A novel ultraperformance liquid chromatography-mass spectrometry-based analytical method for the determination of DA, acetyl propionyl, glyoxal, and methylglyoxal was developed and validated. Next, eight commercially available cig-a-like-type EVPs were evaluated for α-dicarbonyl formation. Increased levels of α-dicarbonyls were observed in the aerosols of all evaluated EVPs compared to their respective e-liquids. Mechanistic studies were conducted using a model microwave reaction system to identify key reaction precursors for DA generated from propylene glycol (PG) and carbon-13-labeled glycerin (GLY). These studies, along with the corresponding retrosynthetic analysis, resulted in the proposed formation pathway where hydroxyacetone is generated from PG and/or GLY. Hydroxyacetone then participates in an aldol condensation with formaldehyde where formaldehyde can also be generated from PG and/or GLY; the resultant product then dehydrates to form DA. This proposed pathway was further investigated through in situ synthetic organic experiments within the model microwave reaction system. This work establishes that DA is formed in the aerosol generation process of the EVPs tested though at levels below toxicological concern.

Biodiversity and dairy traits of indigenous milk lactic acid bacteria grown in presence of the main grape polyphenols.

The present work was developed to select lactic acid bacteria (LAB) to be used as starter cultures in functional cheese production. The indigenous milk LAB populations were isolated from fermented raw ewes' milks (four bulks) added with 0.5mg/mL of nine polyphenols commonly found in winery by-products. After 48h of fermentation, all milks were characterized by an increase of LAB levels of about 3-4 Log cycles. All different colonies were purified and characterized for the main physiological and biochemical traits and then differentiated genetically at strain level and identified. Ten species belonging to the LAB genera Lactobacillus, Streptococcus, Enterococcus, Leuconostoc and Lactococcus were identified. Only Lactococcus lactis and Leuconostoc mesenteroides strains were evaluated for the technological traits including acidification and autolytic kinetics, diacetyl formation, exopolysaccharide production and generation of antimicrobial compounds. A total of four strains (Mise36, Mise94 Mise169 and Mise190) belonging to Lc. lactis displayed potential for production of cheeses containing grape polyphenols.

A Laboratory Method for Determining Bacterially Formed Odorants and Reducing Odor in Absorbent Incontinence Products.

The purpose of this study was to design a laboratory test method to mimic the formation of bacterially formed odorants during the use of absorbent urinary incontinence products. Three odor inhibitors with different modes of action were tested and evaluated. Bacterially formed odorants in incontinence products were evaluated by adding a synthetic urine inoculated with a mixture of 4 bacterial strains to product samples cut from the incontinence products. The product samples were incubated in sealed flasks. The odorants that formed in the head space were sampled onto adsorbent tubes and analyzed by gas chromatography. The inhibitory effects of low pH, ethylenediaminetetraacetic acid (EDTA), and activated carbon were then measured. This technique enabled production of known odorants 3-methylbutanal, guaiacol, diacetyl, and dimethyl disulfide (DMDS) in concentrations of 50 to 600 ng/L in incontinence products. The method was further evaluated by testing 3 types of odor inhibitors; EDTA significantly reduced formation of all 4 odorants (P < .001). Lowering the pH from 6.0 to 4.9 decreased levels of 3-methylbutanal, DMDS, and guaiacol (P < .001); however, diacetyl levels increased (P < .001). Activated carbon significantly reduced the formation of diacetyl, DMDS, guaiacol, and 3-methylbutanal (P < .001). The technique we developed can be used to evaluate inhibitors with different modes of action to determine odor control in incontinence products. The odorants formed are produced by bacteria and have been identified as key contributors to the odor of used incontinence products. This work can be a step toward establishing a standard in the field of incontinence and odor control; creation of a standard will help the health care sector compare products to be purchased and benefit patients through the development of better products.

Fabrication of Various Carbon Nanotube/Nickel Nanocomposite Powders by Polyol Process.

We developed a molecular level mixing process for fabricating various types of carbon nanotube (CNT)/nickel (Ni) nanocomposite powders by a polyol process. A CNT/Ni nanocomposite was fabricated by two steps, dehydration of polyol and oxidation of acetaldehyde with the formation of diacetyl. Oxygen functionalized CNTs offer direct nucleation sites for Ni particles and strong chemical bonding between CNT and Ni particles. By controlling nucleation sites and nuclear growth, we successfully fabricated three different types of nanocomposite powders, CNT implanted Ni, Ni coated CNTs, and Ni decorated CNTs. Each type of powder was developed for various applications. During the sintering process, the implanted type retained CNT's crystal structure. As a conductive filler to other matrix, the coated and decorated type offered homogeneous dispersion and an enhanced conductive network. Various types of CNT/Ni nanocomposite powders show potential for remarkable development of bulk scale fabrication where exceptionally high strength and electric conductivity is necessary.

Acetoin is a precursor to diacetyl in e-cigarette liquids

Use of the e-liquid flavourings diacetyl and acetyl propionyl has raised concerns that they might cause respiratory diseases amongst vapers. Product surveys show that these compounds, plus a less toxic alternative, acetoin, are widely used in e-liquids.We have investigated the chemistry of acetoin, acetyl propionyl and diacetyl in e-liquids. They are reactive, with concentrations falling substantially over time. Acetyl propionyl is the most reactive, diacetyl less so, and acetoin significantly more stable. Their reactivity is pH-enhanced when nicotine is present in the e-liquid.Of major concern, we found that acetoin generates diacetyl in e-liquids. We found diacetyl formation in all acetoin-containing e-liquids, but it is not an acetoin-contaminant. Diacetyl concentrations were proportional to acetoin content, grew over time, and formation was accelerated by nicotine. E-liquids stored for up to 18 months contained significant diacetyl, and reduced acetoin levels, showing that acetoin is a long-term diacetyl source. Other reaction pathways operate, and we advance mechanisms to explain this area of e-liquid chemistry.Acetoin use in e-liquids is an inevitable source of diacetyl exposure for e-cigarette users. Acetoin, acetyl propionyl and diacetyl are avoidable hazards for vapers, and we recommend e-liquid manufacturers move away from their use in e-liquid formulations.

Effect of Respiratory Growth on the Metabolite Production and Stress Robustness of Lactobacillus casei N87 Cultivated in Cheese Whey Permeate Medium.

Cheese whey permeate (WP) is a low-cost feedstock used for the production of biomass and metabolites from several lactic acid bacteria (LAB) strains. In this study, Lactobacillus casei N87 was cultivated in an optimized WP medium (WPM) to evaluate the effect of anaerobic and respiratory conditions on the growth performances (kinetics, biomass yield), consumption of sugars (lactose, galactose, glucose) and citrate, metabolite production [organic acids, volatile organic compounds (VOCs)] and stress survival (oxidative, heat, freezing, freeze-drying). The transcription of genes involved in the main pathways for pyruvate conversion was quantified through Real Time-PCR to elucidate the metabolic shifts due to respiratory state. Cultivation in WPM induced a diauxic growth in both anaerobic and respiratory conditions, and L. casei N87 effectively consumed the lactose and galactose present in WPM. Genomic information suggested that membrane PTS system and tagatose-6-P pathway mediated the metabolism of lactose and galactose in L. casei N87. Respiration did not affect specific growth rate and biomass production, but significantly altered the pyruvate conversion pathways, reducing lactate accumulation and promoting the formation of acetate, acetoin and diacetyl to ensure the redox balance. Ethanol was not produced under either cultivation. Pyruvate oxidase (pox), acetate kinase (ack), α-acetolactate decarboxylase (ald), acetolactate synthase (als) and oxaloacetate decarboxylase (oad) genes were up-regulated under respiration, while L-lactate dehydrogenase (ldh), pyruvate formate lyase (pfl), pyruvate carboxylase (pyc), and phosphate acetyltransferase (pta) were down regulated by oxygen. Transcription analysis was consistent with metabolite production, confirming that POX-ACK and ALS-ALD were the alternative pathways activated under aerobic cultivation. Respiratory growth affected the production of volatile compounds useful for the development of aroma profile in several fermented foods, and promoted the survival of L. casei N87 to oxidative stresses and long-term storage. This study confirmed that the respiration-based technology coupled with cultivation on low-cost medium may be effectively exploited to produce competitive and functional starter and/or adjunct cultures. Our results, additionally, provided further information on the activation and regulation of metabolic pathways in homofermentative LAB grown under respiratory promoting conditions.

Screening of aroma-producing lactic acid bacteria and their application in improving the aromatic profile of yogurt.

The development of yogurt flavor is a complicated and dynamic biochemical process. In addition to traditional starter cultures, adjunct cultures could also make significant contributions to the flavor profiles of yogurt. In the current study, two Lactobacillus plantarum strains (1-33 and 1-34) were isolated based on their abilities to produce acetaldehyde and diacetyl. In co-fermentation with traditional starters, these isolated strains were able to maintain viability without affecting the yogurt's acidification profiles. Furthermore, they positively influenced the aroma quality of the yogurt samples. They promoted the formation of volatile metabolites, especially acetaldehyde, diacetyl, and acetoin, which are recognized as characteristic compounds. The results of this work provide novel knowledge about the contributions of isolated strains on the flavor profiles of yogurt, which will help to improve the organoleptic properties of the final products. PRACTICAL APPLICATIONS: Using lactic acid bacteria (LAB) as adjunct cultures co-fermented with traditional yogurt starter cultures can increase the quantities of flavor compounds in yogurt. This study enriches our understanding of the effects of adjunct cultures on yogurt flavor. Researchers and manufacturers that specialize in yogurt making can use the results of this study to improve the aromatic profile and organoleptic quality of yogurt.

Lifestyle of Lactobacillus hordei isolated from water kefir based on genomic, proteomic and physiological characterization

Water kefir is a traditional fermented beverage made from sucrose, water, kefir granules, dried or fresh fruits. In our water kefir granules, Lactobacillus (L.) hordei is one of the predominant lactic acid bacteria (LAB) species of this presumed symbiotic consortium. It faces abundant sucrose versus limitation of amino- and fatty acids in an acidic environment. Sequencing of the genome of L. hordei TMW 1.1822 revealed one chromosome plus three plasmids. The size of the chromosome was 2.42 Mbp with a GC content of 35% GC and 2461 predicted coding sequences. Furthermore, we identified 1474 proteins upon growth on water kefir medium. Metabolic prediction revealed all enzymes required for the glycolytic Embden-Meyerhof (EMP) and phosphoketolase (PKP) pathways. Genes encoding all enzymes involved in citrate, pyruvate and mannitol metabolism are present.Moreover, it was confirmed that L. hordei is prototrophic for 11 amino acids and auxotrophic for 6 amino acids when combining putative biosynthesis pathways for amino acids with physiological characterization. Still, for glycine, serine and methionine no sure auxotype could be determined. The OppABCDF peptide transport system is complete, and 13 genes encoding peptidases are present. The arginine deiminase system, was predicted to be complete except for carbamate kinase, thus enabling neutralization reactions via ammonium formation but no additional energy generation. Taken together our findings enable prediction of the L. hordei lifestyle in water kefir: Abundant sucrose is consumed directly via parallel EMP and PK pathways and is also extracellularly converted to dextran and fructose by a glucansucrase, leaving fructose as additional carbon source. Essential amino acids (in the form of peptides) and citrate are acquired from fruits. In the lack of FabB unsaturated fatty acids are synthesized by predicted alternative enzymes. Formation of acetoin and diacetyl as well as arginine conversion reactions enable acidification limitation. Other members of the water kefir consortium (yeasts, acetic acid bacteria) likely facilitate or support growth of L. hordei by delivering gluconate, mannitol, amino- and fatty acids and vitamins.

Enhanced Wort Fermentation with De Novo Lager Hybrids Adapted to High-Ethanol Environments.

Interspecific hybridization is a valuable tool for developing and improving brewing yeast in a number of industry-relevant aspects. However, the genomes of newly formed hybrids can be unstable. Here, we exploited this trait by adapting four brewing yeast strains, three of which were de novo interspecific lager hybrids with different ploidy levels, to high ethanol concentrations in an attempt to generate variant strains with improved fermentation performance in high-gravity wort. Through a batch fermentation-based adaptation process and selection based on a two-step screening process, we obtained eight variant strains which we compared to the wild-type strains in 2-liter-scale wort fermentations replicating industrial conditions. The results revealed that the adapted variants outperformed the strains from which they were derived, and the majority also possessed several desirable brewing-relevant traits, such as increased ester formation and ethanol tolerance, as well as decreased diacetyl formation. The variants obtained from the polyploid hybrids appeared to show greater improvements in fermentation performance than those derived from diploid strains. Interestingly, it was not only the hybrid strains, but also the Saccharomyces cerevisiae parent strain, that appeared to adapt and showed considerable changes in genome size. Genome sequencing and ploidy analysis revealed that changes had occurred at both the chromosome and single nucleotide levels in all variants. Our study demonstrates the possibility of improving de novo lager yeast hybrids through adaptive evolution by generating stable and superior variants that possess traits relevant to industrial lager beer fermentation.IMPORTANCE Recent studies have shown that hybridization is a valuable tool for creating new and diverse strains of lager yeast. Adaptive evolution is another strain development tool that can be applied in order to improve upon desirable traits. Here, we apply adaptive evolution to newly created lager yeast hybrids by subjecting them to environments containing high ethanol levels. We isolated and characterized a number of adapted variants which possess improved fermentation properties and ethanol tolerance. Genome analysis revealed substantial changes in the variants compared to the original strains. These improved variant strains were produced without any genetic modification and are suitable for industrial lager beer fermentations.

THERMAL DECOMPOSITION OF ELECTRONIC CIGARETTE LIQUID. IR STUDY

Under the conditions which are characteristic for electron cigarette usage chemicals containing in cigarettes (nicotine (0-2% weight usually), propylene glycol, glycerol, distilled water and different flavors) are capable to thermal decomposing and the products of decomposition could react with each other. Thus, harmful compounds and carcinogens may evolve. Literature describes a number of experiments detecting the formation of tobacco-specific nitrosamines, diacetyl and acetyl propionyl, toluene, ethyl benzene, o-, m-, p-xylene, formaldehyde, acetaldehyde, acetone, propenal, glyoxal.The present contribution describes our efforts to study the composition of vapors over the liquids for electronic cigarettes containing no flavors by means of IR-spectroscopy. The temperature range was 20 to 400 °C, and flow of air and argon was used. The electronic cigarette liquid was found to emit aqueous vapor, carbon dioxide, propylene glycol and glycerol mostly. Propenal was also detected in vapors in argon atmosphere at temperature of ~350 °C. No other compounds were found in neither liquid phase by 1H, 13C NMR spectroscopy after heating to 150 oC or vapors at temperature lower than 250 °C.Forcitation:Gamov G.A., Smirnov N.N., Aleksandriiskii V.V., Sharnin V.A. Thermal decomposition of electronic cigarette liquid. Ir study. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N2. P. 7-12.

THERMAL DECOMPOSITION OF ELECTRONIC CIGARETTE LIQUID. IR STUDY

Under the conditions which are characteristic for electron cigarette usage chemicals containing in cigarettes (nicotine (0-2% weight usually), propylene glycol, glycerol, distilled water and different flavors) are capable to thermal decomposing and the products of decomposition could react with each other. Thus, harmful compounds and carcinogens may evolve. Literature describes a number of experiments detecting the formation of tobacco-specific nitrosamines, diacetyl and acetyl propionyl, toluene, ethyl benzene, o-, m-, p-xylene, formaldehyde, acetaldehyde, acetone, propenal, glyoxal.The present contribution describes our efforts to study the composition of vapors over the liquids for electronic cigarettes containing no flavors by means of IR-spectroscopy. The temperature range was 20 to 400 °C, and flow of air and argon was used. The electronic cigarette liquid was found to emit aqueous vapor, carbon dioxide, propylene glycol and glycerol mostly. Propenal was also detected in vapors in argon atmosphere at temperature of ~350 °C. No other compounds were found in neither liquid phase by 1H, 13C NMR spectroscopy after heating to 150 oC or vapors at temperature lower than 250 °C.Forcitation:Gamov G.A., Smirnov N.N., Aleksandriiskii V.V., Sharnin V.A. Thermal decomposition of electronic cigarette liquid. Ir study. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N2. P. 7-12.

Enzyme-inorganic nanoflowers/alginate microbeads: An enzyme immobilization system and its potential application

Abstract In this work, novel nanoflower/alginate microbeads were synthesized to immobilize α-acetolactate decarboxylase (ALDC) with a facile approach. Typically, ALDC was first coprecipitated with Ca3(PO4)2 to form enzyme-inorganic hybrid nanoflowers (Ca3(PO4)2-ALDC), and then the nanoflowers containing micrometre-sized particles and nanoscale flower-like petals were entrapped in alginate gel beads (Ca3(PO4)2-ALDC) @Alg). Compared with free ALDC and Ca3(PO4)2-ALDC nanoflowers, the microbeads performed greatly improved recyclability and stability, meanwhile, retained 98% of activity compared with free ALDC. Moreover, the immobilized enzyme can be used in a 300 L beer fermentation tank to prevent the formation of diacetyl, solve the problem of beer off-flavor and short the beer maturation time, thus exhibiting a great potential application in beer brewing industry.

Зниження вмісту віцинальних дікетонів при зброджуванні високогустинного сусла

Одним із завдань високогустинного пивоваріння як сучасної енергоощадної технології є отримання пива високої якості, адже смак і аромат напою ‒ його головні споживчі властивості. Віцинальні дікетони ‒ діацетил (2,3-бутандіон) та 2,3-пентандіон – відіграють значну роль у формуванні смаку. Завдання пивоварів полягає в зведенні до мінімуму їх утворення або пришвидшенні їх відновлення до речовин із вищим порогом відчуття. До основних методів зниження вмісту дікетонів належать оптимізація параметрів бродіння та дозрівання, використання модифікованих штамів дріжджів та іммобілізованих дріжджових клітин. Цього досягають також застосуванням ферменту α-ацетолактатдекарбоксилази, який міститься в ферментному препараті Матурекс. Він каталізує реакцію перетворення α-ацетолактату безпосередньо в ацетоїн, минаючи утворення діацетилу. Таким чином значно знижується вміст дікетонів у пиві та скорочується тривалість його дозрівання. В роботі досліджено вплив параметрів зброджування високогустинного сусла – концентрації сухих речовин у суслі, температури та тривалості процесу на вміст дікетонів у пиві. Визначено оптимальні умови головного бродіння: концентрація сусла 16% сухих речовин, температура бродіння 15 °С, тривалість 7 діб. Встановлено вплив дози ферментного препарату Матурекс 1, 2 і 3 г на 1 гл сусла на вміст віцинальних дікетонів у молодому пиві. Визначено оптимальну дозу препарату, яка становить 2 г на 1 гл сусла. Досліджено вплив ферментного препарату Матурекс на фізико-хімічні показники молодого та готового пива – вміст екстракту та етанолу, рН і кислотність, вміст віцинальних дікетонів. Таким чином, для пришвидшення процесів дозрівання пива в технології високогустинного пивоваріння, зниження вмісту віцинальних дікетонів у пиві та збільшення ефективності виробництва можна рекомендувати зброджування сусла концентрацією 16% сухих речовин при температурі 15 °С впродовж 7 діб з додаванням ферментного препарату Матурекс у кількості 2 г на 1 гл сусла.

Effects of Sodium Chloride, Potassium Chloride, and Calcium Chloride on the Formation of α-Dicarbonyl Compounds and Furfurals and the Development of Browning in Cookies during Baking.

Effects of NaCl, KCl, CaCl2, NaHCO3, and NH4HCO3 on the formation of glucosone, 1-deoxyglucosone, 3-deoxyglucosone, glyoxal, methylglyoxal, diacetyl, 5-hydroxymethyl-2-furfural, and 2-furfural and browning were investigated in cookies. The presence of 1.5% NaCl, 1% KCl, and 1% CaCl2 on flour basis had no effect on α-dicarbonyl compounds, except 1-deoxyglucosone increased in the presence of KCl and CaCl2. The increase in 5-hydroxymethyl-2-furfural formation in the presence of NaCl, KCl, and CaCl2 did not relate to 3-deoxyglucosone formation and pH changes. NaCl, KCl, and CaCl2 increased browning in cookies. Model reaction systems indicated that NaCl, KCl, and CaCl2 enhance browning by increasing furfurals in caramelization. NaCl, KCl, and CaCl2 decreased browning intensity in a heated glucose-glycine system. Use of CaCl2 in cookies may considerably increase furfurals but not α-dicarbonyl compounds. Sodium reduction can be obtained by replacement with potassium without sacrificing the desired consequences of caramelization in sugar-rich baked goods.

Surface-engineered Saccharomyces cerevisiae displaying α-acetolactate decarboxylase from Acetobacter aceti ssp xylinum.

To convert α-acetolactate into acetoin by an α-acetolactate decarboxylase (ALDC) to prevent its conversion into diacetyl that gives beer an unfavourable buttery flavour. We constructed a whole Saccharomyces cerevisiae cell catalyst with a truncated active ALDC from Acetobacter aceti ssp xylinum attached to the cell wall using the C-terminal anchoring domain of α-agglutinin. ALDC variants in which 43 and 69 N-terminal residues were absent performed equally well and had significantly decreased amounts of diacetyl during fermentation. With these cells, the highest concentrations of diacetyl observed during fermentation were 30% less than those in wort fermented with control yeasts displaying only the anchoring domain and, unlike the control, virtually no diacetyl was present in wort after 7days of fermentation. Since modification of yeasts with ALDC variants did not affect their fermentation performance, the display of α-acetolactate decarboxylase activity is an effective approach to decrease the formation of diacetyl during beer fermentation.