Influence of yeast strain on binding of sulphur dioxide in wines,and on its formation during fermentation

The amounts of sulphur dioxide bound by acetaldehyde, pyruvic acid and α-ketoglutaric acid during fermentation of three grape juices by eight wine yeasts (Saccharomyces sp.) are reported. These constituents accounted for 49–83 % (mean 69) of the measured bound SO₂, depending on the yeast strain and juice. the maximum range of concentrations of the binding components for individual wines were 10–48 ppm for acetaldehyde, 9–77 ppm for pyruvic acid and 5–63 ppm for α-ketoglutaric acid, depending on yeast strain and grape juice. the validity of the calculations was verified by an experiment with SO₂ and the three binding compounds in a multicomponent model system. The acetaldehyde content was related to the total SO₂ present, which itself was determined by the strain of yeast. SOz bound in the wines after a further SO₂ addition was correlated significantly with pyruvic and α-ketoglutaric acids, but not with acetaldehyde. Certain yeasts produced SO₂ during fermentation in grape juice and in synthetic media with defined sulphur sources. More SO₂ was produced at pH 3.6 than 3.0 in the absence of added sulphate in grape juice. Sulphate was the best sulphur source for SO₂ production in synthetic media, although some yeasts were able to produce smaller amounts of SO₂ from l-cysteine and reduced glutathione.     

Formation of the highly stable pyranoanthocyanins (vitisins A and B) in red wines by the addition of pyruvic acid and acetaldehyde

Pyruvic acid (500 mg/l) and acetaldehyde (200 mg/l) were added, either as a large single dose or as smaller weekly doses over a 10 week period, to a young red wine (Vitis vinifera L. cv Tempranillo) in order to study the formation of vitisin A and B, and p-coumaroylvitisin A and B. In a further trial, pyruvic acid and acetaldehyde were added simultaneously as a single administration to test for any synergistic effect on vitisin formation. The addition of pyruvic acid led to the production of higher concentrations of vitisin A (4.08 ± 0.86 mg/l; 2.03% of the total anthocyanin content), while additions of acetaldehyde increased the concentration of vitisin B (2.47 ± 0.09 mg/l; 1.35%). The single, large dose administrations led to greater vitisin formation than did the smaller, weekly doses. Different patterns of formation were seen for vitisin A and B: the highest vitisin A content was achieved during the latter half of the 10 week study period while the highest vitisin B concentration was achieved early. The addition of acetaldehyde produced a greater reduction in monomeric anthocyanins than did the addition of pyruvic acid (loss of total anthocyanins 81.5%). The simultaneous addition of pyruvic acid and acetaldehyde led to less vitisin formation than did the addition of the reagents separately. p-Coumaroylvitisin A reached a maximum concentration of 0.86 ± 0.15 mg/l when the single dose of pyruvic acid was added, while the maximum recorded for p-coumaroylvitisin B was 0.66 ± 0.05 mg/l when the single dose of acetaldehyde was added. All anthocyanins were identified using HPLC/DAD and HPLC/ESI–MS.     

On the combination of sulphite with food ingredients (aldehydes, ketones and sugars). II.

Summary Three kinds of combined sulphites (bisulphite adducts of acetaldehyde, pyruvic acid and D-mannose), different in combination strength, were prepared to provide a model system for comparative studies on the accuracy of several determination methods for combined sulphites. The purity of the combined sulphites, obtained either as crystals or amorphous powder, was shown to be not less than 99%.Five methods, formerly applied on the determination of residual sulphites in foods, were subjected to the determination of these combined sulphites. A modified Monier-Williams method, iodimetry and distillation-colorimetry were effective for the determination of combined sulphite, whilst a microdiffusion method and direct colorimetry (by use of mercuric chloride) were shown to be inadequate for the determination of combined sulphite.Three combined sulphites were shown to be produced by the reaction between free sulphite and acetaldehyde, pyruvic acid or D-mannose at room temperature within a short time in the weak acid to slightly alkaline pH range. About 50% of combined sulphite were produced by the reaction of equimolar amounts of sodium bisulphite and acetaldehyde or pyruvic acid.

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Über die Bindung des Sulfits an Lebensmittelbestandteilen (Aldehyde, Ketone und Zucker). II.

Zusammenfassung Es wird die Darstellung der Bisulfit-Anlagerungsverbindungen von Acetaldehyd, Brenztraubensäure undd-Mannose beschrieben. Die Reinheit der gen. Verbindungen beträgt 99%.fünfAn Hand dieser Verbindungen wird überprüft, welche von fünf Standardmethoden zur Sulfitbestimmung in Lebensmitteln für die Bestimmung des gebundenen Sulfits geeignet ist. Hierbei ergeben die abgeänderte Monier-Williams-Methode, die Jodometrie und die Wasserdampfdestillation/Colorimetrie befriedigende Ergebnisse, während die Mikrodiffusion und die direkte Colorimetrie ungeeignet erscheinen.Die gen. Anlagerungsverbindungen bilden sich bei Zimmertemperatur im schwach sauren bis schwach alkalischen Milieu innerhalb kurzer Zeit. In einer äquimolaren Lösung aus Acetaldehyd bzw. Brenztraubensäure und Natriumhydrogensulfit liegt nach kurzer Zeit 50% des Sulfits als Anlagerungsverbindung vor.

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Studies on the Analyses of Sulphites in Food (II)     

Crystallization and some properties of D-lactate dehydrogenase from Staphylococcus sp. LDH-1

Staphylococcus sp. LDH-1 isolated as a high producer of lactate dehydrogenase grew well under anaerobic conditions and produced a large amount of D-lactate dehydrogenase (D-LDH), but not L-LDH. After purification of this D-LDH, some properties were revealed. The enzyme catalyzed the reversible reduction of 2-oxo acids into D-2-hydroxy acids, but not into L-2-hydroxy acids. The K(m) values for 2-oxo acids were much smaller than those for D-2-hydroxy acids, and the V(max) values for 2-oxo acids were much greater than those for D-2-hydroxy acids. The equilibrium constants for the reaction of the reductions of pyruvic acid to D-lactic acid and of 2-oxobutyric acid to D-2-hydroxy-n-butyric acid were 270 and 360, respectively. The enzyme was stable between pH 5.5 and 8.5, while the optimum pH for pyruvic acid and D-lactic acid was pH 5.0 and 8.2, respectively. It was therefore concluded that the D-LDH from Staphylococcus sp. LDH-1 is available as enzyme for an assay of pyruvic acid and for the production of D-2-hydroxy acids.     

Organic acids and volatile flavor components evolved during refrigerated storage of kefir

Kefir samples were prepared and transferred to sterile jars for storage at 4 degrees C. After 0, 7, 14, and 21 d of storage, the pH, organic acid, and volatile flavor component content were determined to monitor possible flavor changes during storage. Stored samples were analyzed for organic acid (orotic, citric, pyruvic, lactic, uric, acetic, propionic, butyric, and hippuric) content by HPLC with UV detection at 275 nm. Acetoin, ethanol, acetaldehyde, and diacetyl were monitored using gas chromatography equipped with a headspace autosampler. There was no significant decrease in average pH of samples between d 0 and 21 of storage (P>0.05). Lactic acid concentration increased during storage, reaching a maximum of 7739 ppm by d 21. Orotic and citric acids increased slightly during storage. Although pyruvic and hippuric acids are produced during fermentation, neither was detected during storage. Acetic, propionic, and butyric acids were not detected during kefir storage. Ethanol concentrations increased during storage and reached 0.08% by d 21. The amounts of acetaldehyde and acetoin, common flavor substances in many cultured dairy products, increased during fermentation. Acetaldehyde content in kefir samples doubled from d 0 to 21, reaching a final concentration of 11 microg/g. During storage, the concentration of acetoin decreased from 25 ppm on d 0 to 16 ppm on d 21. However, diacetyl, another common flavor component in cultured dairy products, was not detected during fermentation or storage.     

两种酸奶后酸化期风味物质的比较研究

比较了传统双菌发酵酸奶和高产γ-氨基丁酸的植物乳杆菌（Lactobacillus plantarum）与双菌复配发酵酸奶在后酸化过程中pH、双乙酰、乙醛及4种有机酸（柠檬酸、丙酮酸、乳酸、甲酸）的变化情况。试验结果显示,以上两种酸奶在后酸化期双乙酰和乙醛含量基本保持一致而有机酸含量差异较大。三菌复配型酸奶中甲酸含量较高而柠檬酸含量较低,其它两种有机酸在两种酸奶中的含量比较接近。上述结果表明,以德式乳杆菌保加利亚亚种（Lb.delbrueckiisubsp.bulgaricus）和嗜热链球菌（Streptococcus thermophilus）复配一定比例高产γ-氨基丁酸的植物乳杆菌为发酵剂制作的酸奶保持了酸奶原有的醇香,还形成了一定独特的风味特点。     

Factors Affecting Zymomonas mobilis subsp. francensis Growth and Acetaldehyde Production

An experimental plan was designed to determine the incidence of factors encountered during cider production on Zymomonas mobilis subsp. francensis growth and acetaldehyde production. Different factor combinations of pH (3.50 to 4.10), SO₂ addition (0, 50, 100 and 200 mg/L), nitrogen source concentrations (0.5 and 5.0 g/L), polyphenol cider marc extract supplementation (0.25 and 1.00 g/L), temperature (12°C, 18.5°C and 25°C) and inoculation level (10² and 10⁵ CFU/mL) were tested over a 30‐day period at regular time intervals in synthetic medium with ethanol. Viable cell counts and acetaldehyde production were correlated. Individually, and in decreasing significance, the following factors influenced acetaldehyde production: nitrogen source, SO₂ addition, inoculation level, temperature and pH. On the other hand, presence of polyphenol cider marc extract was not significant. A model was determined based on factor interactions. At high contamination levels (10⁵ CFU/mL), conditions leading to a high risk for spoilage were observed at pH values ranging from 3.75 to 4.10, at 0 to 50 mg/L total SO₂ and in the presence of 5 g/L nitrogen source (yeast extract) while temperature did not in fact appear to play a key role. At lower contamination levels (10² CFU/mL), the risk was drastically reduced. The only conditions leading to increased acetaldehyde levels were a high pH 4.1, no added SO₂ and high nitrogen source concentration (5 g/L yeast extract).     

Effect of six organic acids on staphylococcal growth and enterotoxin production.

Four Staphylococcus aureus strains were incubated at 37 degrees C for 24 h in broth progressively acidified with lactic, citric, ascorbic, acetic, pyruvic and propionic acids, and their survival rate and enterotoxin producing ability was studied. Acids were chosen based on their frequent use by the food industry. Periodically, samples were withdrawn to determine counts, pH and the presence of enterotoxins A, B, C, and D. For a given acid, the effect on growth and enterotoxin synthesis was different. The most inhibitory acid for the growth of strains FRI-100 and FRI-472 was pyruvic acid, for strain FRI-137 was lactic acid, all six acids were equally effective on strain S6. Lactic acid was very inhibitory to enterotoxin synthesis, but the effect on this parameter of acetic and citric acids was almost nil. Enterotoxins were seen to be inactivated at acid pH values; enterotoxin B was the most resistant to inactivation.     

Breeding of high-pyruvate-producing Torulopsis glabrata with acquired reduced pyruvate decarboxylase

An efficient method for isolation of pyruvate-producing mutants of Torulopsis glabrata IFO 0005 was established. On mutagenesis of the parent strain, mutants requiring acetate for complete growth were isolated. The acetate-leaky auxotrophic mutants demonstrated higher fermentative yields of pyruvate from glucose than the parent strain. Thus, the pyruvate decarboxylase (PDC) activity of mutants requiring acetate for complete growth was lower than that of the parent strain. A decrease in the PDC activity would therefore block the formation of acetate via acetaldehyde and thus increase pyruvate production. Among the mutants, T. glabrata ACII-33 had accumulated free pyruvic acid (60.3 g/l) in 47 h (yield, 67.3%; conversion of pyruvic acid from glucose consumed) in a 3 l jar-fermentor. This yield by strain ACII-33 represented at 15% increase compared to that with the parent strain.     

Microbiological and fermentation characteristics of togwa,a Tanzanian fermented food

Selected microbiological and metabolic characteristics of sorghum, maize, millet and maize-sorghum togwa were investigated during natural fermentation for 24 h. The process was predominated by lactic acid bacteria (LAB) and yeasts. The mesophiles, lactic acid bacteria, and yeasts increased and the Enterobacteriaceae decreased to undetectable levels within 24 h. The isolated microorganisms were tentatively identified as Lactobacillus plantarum, Lactobacillus brevis, Lactobacillus fermentum, Lactobacillus cellobiosus, Pediococcus pentosaceus, Weissella confusa, Issatchenkia orientalis, Saccharomyces cerevisiae, Candida pelliculosa and Candida tropicalis. The pH decreased from 5.24-5.52 to 3.10-3.34. Maltose increased initially and then decreased, fructose decreased and glucose levels increased during the first 12 h of fermentation. The organic acids detected during fermentation included DL-lactic, succinic, formic, pyruvic, citric, pyroglutamic and uric acid. Lactate was the predominant acid and increased significantly with time. The volatile organic compounds (VOC) detected included acetaldehyde, 2-methyl-propanal, 2-methyl-butanal, 3-methyl-butanal, ethanol, 2-methyl-1-propanol, 2-methyl-1-butanol, 3-methyl-1-butanol, diacetyl and acetoin. Ethanol was the predominant VOC and it increased significantly with time.     

MALIC DEHYDROGENASES FROM DIOSCOREA ROTUNDATA TUBERS: PURIFICATION AND PROPERTIES OF TWO ISOZYMES

Two molecular forms of the enzyme malate dehydrogenase (MDH₁ and MDH₂) have been purified from Dioscorea rotundata tubers. The enzymes were resolved on a DEAE-cellulose column and found to be homogeneous with differential mobilities on polyacrylamide gels. Both enzymes appeared to be dimeric proteins with subunit molecular weights of 30, 100 ± 50 and 31,600 ± 250 for MDH₁ and MDH₂, respectively. The enzymes exhibited maximal catalytic activity within the pH range 6.57.5 at 37C and were inhibited by oxaloacetic acid at concentrations greater than 0.25 mM as well as other naturally occurring metabolites (citric acid, isocitric acid, a-hetoglutaric acid, succinic acid, pyruvic acid, aspartic acid, glutamic acid, ATP and ADP). The thermal stability and storability of the enzymes at different conditions were significantly different.     

Reducing the sulfur-dioxide binding power of sweet white wines by solid-phase extraction

The high sulfur-dioxide binding power of sweet white wines may be reduced by extracting the naturally present carbonyl compounds from wine that are responsible for carbonyl bisulphites formation. The carbonyl compounds mainly responsible for trapping SO₂ are acetaldehyde, pyruvic acid, and 2-oxoglutaric acid. The method employed was selective solid phase extraction, using phenylsulfonylhydrazine as a scavenging agent. The scavenging function was grafted onto a support prepared from raw materials derived from lignin. This approach is more acceptable to winemakers than the polymer media previously reported, as it reduces the possible contamination of wine to molecules already present in the wine making process.     

Acetaldehyde tolerance in Saccharomyces cerevisiae involves the pentose phosphate pathway and oleic acid biosynthesis

To identify genes responsible for acetaldehyde tolerance, genome‐wide screening was performed using a collection of haploid Saccharomyces cerevisiae strains deleted in single genes. The screen identified 49 genes whose deletion conferred acetaldehyde sensitivity, and these were termed the genes required for acetaldehyde tolerance. We focused on six of these genes required for acetaldehyde tolerance, ZWF1, GND1, RPE1, TKL1 and TAL1, which encode enzymes in the pentose phosphate pathway (PPP), and OAR1, which encodes for NADPH‐dependent 3‐oxoacyl‐(acyl‐carrier‐protein) reductase. These genes were not only responsible for acetaldehyde tolerance but also turned out to be induced by acetaldehyde. Moreover, the content of oleic acid was remarkably increased in yeast cells under acetaldehyde stress, and supplementation of oleic acid into the media partially alleviated acetaldehyde stress‐induced growth inhibition of strains disrupted in the genes required for acetaldehyde tolerance and OLE1. Taken together, our data suggest that the supply of NADPH and the process of fatty acid biosynthesis are the key factors in acetaldehyde tolerance in the yeast, and that oleic acid plays an important role in acetaldehyde tolerance. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of high-pressure homogenisation on metabolic potential of Lacticaseibacillus paracasei 90: in vitro and in situ studies in fermented milk and semihard cheese

The influence of high-pressure homogenisation (HPH) at 100 MPa on Lacticaseibacillus paracasei 90 (L90) was studied in vitro and in situ (fermented milk and cheese). Lysis and injury signs were observed in cells treated with HPH, which were linked to the release of intracellular enzymes and changes in the metabolic activity of L90. HPH treatment led to a higher lactic acid content and lower pH and pyruvic acid levels in fermented milk. The microbiological and peptide profiles of cheeses were modified by using cells or cell-free extracts of L90. Finally, this study suggests that L90 could release bioactive peptides.     

Effect of added α-ketoglutaric acid,pyruvic acid or pyridoxal phosphate on proteolyis and quality of Cheddar cheese

Cheddar cheese curds were supplemented with 1, 5 or 20 g of α-ketoglutarate or pyruvic acid or 1.2 g pyridoxal-5¹-phosphate/kg cheese curd. The higher levels of keto-acids (5 or 20 g/kg curd) caused undesirable changes in the physico-chemical properties of resultant cheese. All levels of α-ketoglutarate reduced the pH of the cheese and promoted syneresis during pressing, while pyruvic acid increased the pH of the cheese. The numbers of starter and non-starter lactic acid bacteria were not affected by the addition of keto-acids or pyridoxal-5¹-phosphate. α-Ketoglutarate or pyruvic acid, at 1 g/kg, or pyridoxal-5¹-phosphatase, at 1.2 g/kg cheese curd, did not influence primary proteolysis in the cheese. The highest and lowest concentrations of total and individual free amino acids were found in the cheeses treated with pyruvic acid or α-ketoglutarate, respectively. The concentrations of most amino acids were lower in the cheeses treated with pyridoxal-5¹-phosphate than in the control. The results of this study suggest that α-ketoglutarate and pyridoxal-5¹-phosphate enhanced the degradation of most amino acids in Cheddar cheese while pyruvic acid promoted the formation of amino acids. The cheeses treated with α-ketoglutarate were more mature than the control cheese of the same age while pyruvic acid-treated cheese had a better flavour than the control.     

Effects of pH, temperature and SO2 on the formation of pyranoanthocyanins during red wine fermentation with two species of Saccharomyces

The formation of vitisins A and B, p-coumaroyl and acetyl derivatives during the fermentation of red wine with two species of Saccharomyces was examined. One species, Saccharomyces cerevisiae strain 7VA was selected for its high production of acetaldehyde and pyruvic acid (7VA). The other (control) species, Saccharomyces uvarum strain S6U is used commercially for wine production. The final vitisins A and B concentrations produced with S. cerevisiae were, respectively, twice and three times that produced with S. uvarum. Models for the formation and accumulation of these vitisins are proposed. This is the first report that the formation of a vinylphenolic derivative of anthocyanin, malvidin-3-O-glucoside-4-vinylguaiacol, can be favored by fermentation with certain yeasts, possibly those with cinnamoyl decarboxylase activity. The effect of SO2, pH and temperature on the formation of pyranoanthocyanins during fermentation with S. cerevisiae and S. uvarum was also analyzed using High Pressure Liquid Chromatography (HPLC)/Photodiode Array Detection. The identification of these compounds was confirmed using HPLC/Electrospray Ionization-Mass Spectrometry.     

缬氨酸转氨酶拆分DL-缬氨酸的催化条件

利用具有缬氨酸转氨酶活性的工程菌对DL-缬氨酸进行拆分,考察了反应温度、pH值、底物摩尔比、底物浓度和金属离子对酶活性和底物转化率的影响。结果显示,该催化反应的最适反应条件为:反应温度是45℃,pH=9,L-缬氨酸与丙酮酸的摩尔比1∶8,DL-缬氨酸初始浓度为0.6 mol/L、丙酮酸初始浓度为2.4 mol/L,0.5 mmol/L的Mg2+和Na+对酶活性有明显的促进作用。     

Effect of pyruvic acid and ascorbic acid on stability of 3‐deoxyanthocyanidins

BACKGROUND: 3‐Deoxyanthocyanins are a rare class of plant pigments primarily found in sorghum and known to possess distinct chemical and bioactive properties. They have potential as natural food colourants. This work investigates how 3‐deoxyanthocyanin pigments react with pyruvic acid and their stability in the presence of ascorbic acid. RESULTS: Substitution at C‐5 was the major determinant of the mechanism of 3‐deoxyanthocyanidin complexation with pyruvic acid: hydroxyl substitution favoured cyclic condensation, whereas methoxyl substitution favoured oxidative ring contraction. Pure 3‐deoxyanthocyanidins generally showed poor stability in the presence of 500 mg L^?1 ascorbic acid at pH 2.0 and 3.2 but were stable at pH 5.0; pyruvic acid improved their stability at pH 2.0 and 3.2 and enhanced their colour intensity at pH 5.0. Crude sorghum pigment extract was very stable in the presence of ascorbic acid: 31% colour loss at pH 2.0; 1.9‐ and 1.3‐fold increases in colour intensity at pH 3.2 and 5.0 respectively. In contrast, red cabbage pigment lost 30–85% of its colour in the presence of ascorbic acid under the conditions used in the study. CONCLUSION: Crude sorghum pigments are very stable in the presence of ascorbic acid and may be useful as natural food colourants. Copyright © 2008 Society of Chemical Industry     

Diacetyl and Acetaldehyde Concentrations During Ripening of Kefalotyri Cheese

Diacetyl and acetaldehyde were determined during ripening of Kefalotyri cheese produced using two different lactic cultures (A: Streptococcus thermophilus + Lactobacillus casei, SI cheese, B: Streptococcus thermophilus + Streptococcus diacetylactis + Streptococcus durans, S2 cheese). Diacetyl increased until the 60th day of ripening (2.49 and 1.62 ppm for S1 and S2 cheese, respectively) and until then was found in higher concentration in trials compared with control (0.91 ppm at 60 days). The possible contribution of lactic acid bacteria, pH and acidity of these cheese on diacetyl during ripening was discussed. Acetaldehyde was detected only until the 15th day of ripening (0.17, 0.20 and 0.08 ppm for control, S1 and S2 cheese, respectively).     

突变型黄单胞杆菌产黄原胶条件的优化

该文对从甘蓝腐烂根部的土壤中分离选育的黄单胞杆菌C2发酵产黄原胶的条件进行了优化。通过单因素试验对培养基（碳源、氮源及碳氮源的浓度）和发酵条件（接种量、发酵时间、温度、pH、装液量）进行优化;为提高黄原胶的胶体性能,在培养中添加不同量的游离丙酮酸。结果表明,液态发酵生产黄原胶的最佳碳源、氮源分别为蔗糖55 g/L,鱼粉10 g/L。黄单胞杆菌C2菌株在接种量为4%,pH值为7,于28 ℃、130 r/min条件下发酵60 h时,黄原胶产量达到34 g/kg。添加游离丙酮酸2 g/L时发酵液黏度为16.0 Pa·s,此时胶体性能最好。