Amounts Of Diacetyl Research Articles

Changes in Diacetyl and Amino Acid Concentration during the Fermentation of Dry-Hopped Beer: A Look at Twelve Saccharomyces Species and Strains

Hops were traditionally used in brewing for the addition of isomerized alpha acids that balance the sugary wort with bitterness, though modern breweries are dry-hopping to add complex and unique aromas to their beers. An unintended consequence of high amounts of dry-hopping is the phenomenon known as hop creep, causing an increase in alcohol, carbonation, and diacetyl concentrations. The amount of diacetyl in a beer can be directly correlated to yeast health and vitality, controlled by the amount of free amino nitrogen (FAN) available to the yeast. In this study, both diacetyl and amino acid concentrations were measured prior to and 24 h after dry-hopping, at terminal gravity, and at the start of fermentation. These values were compared across twelve yeasts that are commonly used in dry-hopped beer or offer unique characteristics to fermentation. Experimental yeasts BY881, WLP518, K-97, and CK S102 all exhibited diacetyl concentrations below the aroma threshold for beer. The addition of dry-hops added a significant (p < 0.05) increase in FAN content to the fermenting beers, with most of the increases in serine, arginine, glutamate/glutamine, alanine, and glycine. These increases did not parallel the amino acid content measured in the grist or hops, where asparagine/aspartic acid, proline, and glutamate/glutamine were most prominent. Correlations between total FAN content and diacetyl concentration were calculated, as diacetyl is a precursor in the biosynthesis pathway of the amino acids valine and leucine. However, in this experiment, no correlation of amino acid and diacetyl concentration was observed between dry-hopped and traditional fermentations.

Effect of the cream cooling temperature and acidification method on the crystallization and textural properties of butter

In this study, techno-functional properties of butter were evaluated by modifying the crystallization and acidification properties of cream. For this purpose, the cream obtained from raw milk was allowed to physically ripen at 6 and 8 °C for different periods (10 and 15 h), after which butter was manufactured by using different acidification methods via addition of lactic acid permeate and natural butter culture. It was observed that cream cooling/crystallization temperature and time, as well as acidification method, affected the physicochemical and technological properties of butter but had no significant impact on sensory properties. In butter samples, palmitic acid, stearic acid and myristic acid were the predominant saturated fatty acids, whereas oleic acid content was the highest among the unsaturated fatty acids. The textural properties and hardness values of control butter manufactured by conventional method were higher. Consequently, it could be concluded that amount of diacetyl, one of the characteristic components of butter, in the cream ripened at 6 °C, and the addition of butter starter culture was higher and the hardness values of the butter manufactured from the cream matured for 15 h was lower in comparison to other samples.

Occurrence and persistence of diacetyl in unfermented and fermented milks

The occurrence and persistence of diacetyl in samples of unfermented raw and processed milk have been investigated; in addition, samples of milk fermented by different lactic acid bacteria have also been analysed. Diacetyl was determined by using a simplified gas chromatographic method in which acetone was the extracting agent. Diacetyl in unfermented raw milk of cow, buffalo, goat and sheep was found to be 45.1, 65.2, 42.8 and 41.2 mg kg−1, respectively. The pre-fermentative diacetyl in milk was highly stable, and its initial value irrelevantly changed after the milk had been stored at 20 °C for 24 h or freeze-dried for 8 h and finally, having been thermically treated at 80 °C for 30 min. Significant amounts of diacetyl were detected also in all the processed milks. At 26 °C growth temperature, the tested lactic acid bacteria produced diacetyl in milk in the following order: Streptococcus thermophilus < Lactobacillus paracasei < Lactobacillus rhamnosus. Diacetyl increased during fermentation of 24 h, while a spontaneous and significant loss was registered when fermentation was prolonged to 48 h.

Antibacterial Activity of Lactic Acid Bacteria Isolated from Salad Vegetables

To determine the inhibitory capacity of lactic acid bacteria (LAB) due to the action of antagonistic substances, 8 members of the LAB group namely, Lactobacillus brevis, Lactobacillus casei, Lactobacillus cellebiosuis, Lactobacillus delbruesckii, Lactobacillus fermentum, Lactobacillus plantarum, Leuconostoc mesenteroides and Pediococci sp were isolated from the surfaces of five salad vegetables. The cell free supernatants of the selected LAB were able to inhibit the growth of the indicator pathogens used in this study. The largest zone of inhibition (18 mm) was produced by L. delbruesckii, L. fermentum and Pediococc i sp. All isolates demonstrated activity and produced diacetyl, hydrogen peroxide and lactic acid to varying degrees and their peak production was found to be during the 48th h. L. cellebiosuis produced the highest amount of diacetyl (2.096 g/l). L. plantarum produced the highest amount of lactic acid (1.801 g/l), while Pediococci sp produced the highest amount of hydrogen peroxide (0.0029 g/l). The sensitivity of the indicator pathogens to these isolates was also investigated by the agar well diffusion method. Resistance was shown to at least two different classes of antibiotics by all the pathogens used. Keywords: salad vegetables, diacetyl, hydrogen peroxide, lactic acid, agar well diffusion

Diacetyl, Acetoin and Acetaldehyde in the Flavour of Doughy Part-Manufactured Goods and Bread, Prepared with Leavens of Lactococci and Lactobacilli

ABSTRACTIt is the Lact, diacetilactis and Lact, cremoris that form the largest amount of diacetyl in the pre-ferment mixed with separately added cultures of lactic acid bacteria and not adding yeast of Sacch. cerevisiae while the L. plantarum and Lact, diacetilactis form the largest amount of acetoin. In that semi-manufacture Lact, lactis and L. bulgaricus form a considerable amount of acetaldehyde. Greater amounts of diacetyl, acetoin and acetaldehyde are found in sour with singly added lactococci unlike the leavens prepared with lactobacilli. The dough showed less content of acetoin and higher of diacetyl. The quantity of the acetaldehyde increases in the dough and to the highest amount in the dough fermented with leaven composed of lactococci in mixture with lactobacilli. Acetoin is formed in the bread crumb as a result of the chemical changes in the acetaldehyde in the process of baking. Part of the diacetyl in the bread crumb originates during the thermal oxidation of acetoin.

Diacetyl Production in Milk by an α-Acetolactic Acid Accumulating Strain of Lactococcus lactis ssp. lactis biovar. diacetylactis

When grown in skim milk, Lacrococcus lactis ssp. lactis biovar. diacetylactis D1 accumulated α-acetolactic acid at 1.7mM because of the absence of α-acetolactate decarboxylase. The α-acetolactic acid produced was unstable and underwent a chemical decarboxylation. At the beginning of the culture, the redox potential was high, and the decarboxylation of α-acetolactic acid produced diacetyl and acetoin. At the end of the culture, the redox potential was low, and α-acetolactic acid was converted into acetoin only. When synthetic α-acetolactic acid was added to skim milk or fermented milk, the chemical decarboxylation of α-acetolactic acid into diacetyl occurred only at high redox potential. The strain D1 has been cultivated under constant agitation, permitting high redox potential to be maintained. In these conditions, diacetyl production was threefold higher than in an unagitated culture. When the strain D1 was cultivated in association with an acidifying Lactococcus lactis ssp. lactis strain, the amount of diacetyl was <.02mM because of the rapid drop of the redox potential at the beginning of the fermentation, which prevented the formation of diacetyl from the chemical oxidative decarboxylation of α-acetolactic acid.

Determination of Diacetyl in Butter as 2,3-Diaminonaphthalene Derivative, Using a Fluorometric Procedure or Reverse Phase Liquid Chromatography with Fluorescence Detection

Abstract Two procedures, one fluorometric and the other reverse phase liquid chromatographic, for determination of a derivative of diacetyl are described. Exploratory work on diacetyl standard solutions to establish the best conditions for the derivatization with 2,3-diaminonaphthalene (DAN) to yield 2,3-dimethylbenzo[g]-quinoxaline (DMBQ) is discussed, as well as the fluorescence characteristics of the DMBQ derivative. Diacetyl was determined in 10 commercial butter samples by the proposed procedures and by other known methods (determination of o-phenylenediamine and 3,3-diaminobenzidinederivatives). Recoveries from butter samples spiked with known amounts of diacetyl ranged from 96.9 to 101.8% (with CVs ranging from 0.3 to 2.1%) for the fluorometric procedure and from 96.9 to 102.7% (with CVs ranging from 0.5 to 2.4%) for the chromatographic procedure. These results agree well with those obtained with o-phenylenediamine and 3,3-diaminobenzidine methods on the same butter samples. The proposed methods have the advantages of improved detectability and specificity.

Characters of Lactobacillus coryniformis, isolated from an Iraqi cheese

The cultural, physiological, and biochemical characters of 21 strains of Lactobacillus coryniformis, isolated from Iraqi cheese, were investigated. Some of the strains grew at 45 degrees C. All possessed the following characteristics: they did not contain DAP; no growth in 4% taurocholate or in 9% NaCl; growth in 6.5% NaCl; milk mostly coagulated within 3 to 60 days with final activity of 0.85--1.09% and pH 4.05; xylose, (D+)tagatose, inulin, and trehalose not fermented; ribose fermented by only one strain and arabinose by another; pyruvate, malate, and fumarate decomposed in the presence of glucose with formation of carbon dioxide; CO2 was produced from gluconate by 20 out of 21 strains. The mean total amount of lactate, produced after 41 days at 30 degrees C, was 42.6 +/- 2.5 mumoles per ml, of L(+)lactate 17.8 +/- 1.1, and of % L(+)lactate of total lactate 42.3 +/- 1.7. The isolates degraded pyruvate (111 mumoles/ml) in the presence of glucose (55.5 mumoles/ml) with lactate as the major product, together with acetate 5.8%, ethanol 8.15%, acetoin 1.95%, and diacetyl 2.50% yield on a molar basis after 60 days at 30 degrees C. Diacetyl and acetoin could be formed from pyruvate plus glucose, but not from either glucose alone, citrate alone, or from citrate plus glucose. The mean total amount of diacetyl plus acetoin, after 26 days at 30 degrees C, was 1059.6 +/- 24.0 micrograms/ml, of diacetyl 92.8 +/- 2.2, and of % diacetyl of the total diacetyl plus acetoin was 8.8 +/- 0.3. L. coryniformis differs from L. plantarum in morphology, in not containing DAP, in failure to grow in 4% taurocholate, in not fermenting ribose and trehalose, and in not decomposing tartrate.

Diacetyl production by Propionibacterium shermanii in milk cultures.

Diacetyl production by propionibacteria in milk cultures was studied using a previously described sensitive method specific for diacetyl. Twenty-four strains belonging to six Propionibacterium species were included in the study. A strain of P. shermanii that produced relatively large amounts of diacetyl in milk was chosen for investigations on factors affecting diacetyl production.Accumulation of the diketone in milk cultures was greater at 21 C than at 32 or 37 C although the rate of production of the compound was greater at the higher temperatures. Rapid cooling after incubation stabilized the diacetyl levels in milk cultures, and prolonged refrigerated holding caused an increase in the concentration of the flavor compound. The dicarbonyl production was greatly affected by the pH of the culture medium, the most favorable range being 4.0 to 4.5. In mixed culture study using a homo-fermentative Streptococcus lactis in combination with the P. shermanii strain, diacetyl production by the latter was greatly enhanced by the rapid pH depression brought about by the streptococci. Diacetyl reductase assays on cell-free extract preparations from the P. shermanii strain showed little or no activity.

Heat-Induced Volatile Compounds in Milk

Milk, preheated at 82C for 30min, was heated to 146C for four seconds and cooled to 5C in a tubular heat exchanger. Immediately after heat treatment, the milk was vacuum distilled at 30C in a semicontinuous, reduced pressure, glass apparatus. Raw milk was distilled in a similar manner for a control. Continuous liquid-liquid ethyl ether extractions were employed to recover the compounds from the aqueous distillates. Gas chromatography, mass spectrometry, infrared spectrophotometry, and odor confirmation were used to characterize the compounds in the ethereal concentrates.The following compounds were found to be heat induced: The C3,4,5,7,8,9,10,11,13n-methyl ketones, the C8,10,12 delta-lactones, benzaldehyde, furfural, phenylacetaldehyde, vanillin, oct-1-en-3-ol, n-heptanol, 2-butoxyethanol, maltol, acetophenone, benzonitrile, benzothiazole, and diacetyl. Other food products could yield these heat-induced compounds provided the basic materials from which they originate were present during the heat treatment. The following novel compounds were found in both heated and raw milk: A dichlorobenzene, a trichlorobenzene, methyl iodide, and diacetyl.Benzonitrile, dichlorobenzene, trichlorobenzene, and methyl iodide were present in the ethereal concentrates in trace amounts.The concentration of diacetyl in heated and raw milk was determined by a modified gas entrainment, on-column trapping GLC technique. The amount of diacetyl in raw milk was 5 ppb, while the amount in the heated milk was 38 ppb, which is above the average flavor threshold for diacetyl in milk. It is suggested that diacetyl contributes to the rich or heated note in the flavor of heated milk.

ビスケットの香気成分(その2)

In this paper, the effect of ingredients on diacetyl formation during baking of model doughs was investigated. The use of various commercial cane sugars in dough resulted in increase of diacetyl formation during the baking process, proportionally with the content of invert sugar. The use of D-glucose, D-fructose, maltose and D-galactose in dough produced more amount of diacetyl than that of D-xylose, lactose, sucrose and raffinose. The effect several shortenings was not found in the diacetyl formation. It was not found that any relation existed between diacetyl formation and protein content of commercial wheat flours. However, the diacetyl formation was remarkably increased by the addition of L-lysine, L-ornithine and other several amino acids. On the basis of these experiments, it was suggested that diacetyl was developed during the baking process, in which the Maillard reaction occurred between amino groups originated from flour and carbonyl compounds originated from cane sugar.

Bacterial production of diacetyl and acetoin in wine.

AbstractWines which have undergone malo‐lactic fermentation contain significantly more diacetyl and acetoin than wines which have not. The amounts of diacetyl and acetoin formed depend on the type of bacterium present and on the composition of the wine. Leuconostoc mesenteroides is the chief organism forming these products in Australian wines while pyruvic acid and citric acid are the chief substrates from which they are formed. The presence of a few g. per litre of glucose interferes with the formation of these products in wine.The heterofermentative rods, Lact. hilgardii and Lact. brevis, which are responsible for malo‐lactic fermentation in some Australian wines, produce diacetyl and acetoin only under conditions unlikely to occur in wines. Homofermentative lactobacilli have not yet been isolated from Australian wines.

A Study of the Diacetyl in Cheese II. The Changes in Diacetyl Content of Cheddar Cheese during Manufacturing and Curing

Summary Diacetyl is produced throughout the manufacturing process of Cheddar cheese except during the interval between setting and cutting. Agitation and increased acidity were factors associated with the increase in diacetyl content. The diacetyl in Cheddar cheese probably is produced by the action of microorganisms upon the citrates in a manner similar to its production in starter cultures. A gradual decrease in the amount of diacetyl in both raw-milk and pasteurized-milk Cheddar cheese was noted during the early stages of curing. This decrease probably is caused by volatilization of the diacetyl and by its reduction to acetylmethylcarbinol and 2,3-butylene glycol as a result of chemical reaction or the action of microorganisms.

318. The effect of acidity on the production of diacetyl by betacocci in milk

1. The diacetyl production of betacocci isolated from starters, cheese and rye-grass was investigated at pR values ranging from 5.5 to 44. The betacocci produced diacetyl and subsequently partially or wholly destroyed it.2. There was a considerable variation in the amount of diacetyl produced by the different strains of betacocci. Capacity to produce diacetyl could not be correlated with any other property of the organisms.3. The rate of growth of the organisms was progressively slower the lower the pH, but at least as much diacetyl was eventually formed at low pK values as at high pH. values. The results showed that there was an alteration in the metabolism of the organisms, the diacetyl-producing power per unit cell increasing with decreasing pH.4. The results found enable an explanation of the rapid production of diacetyl in mixed starters to be offered.

Changes in the Diacetyl and the Acetylmethylcarbinol Contents during the Manufacture of Butter

Summary Marked changes in diacetyl content, both decreases and increases, were noted during the neutralization and pasteurization of sour cream. The changes in the acetylmethylcarbinol content were relatively small. Progressive increases in diacetyl were found after mixing regular butter culture with pasteurized cream (either sweet or sour), after holding the mixture at a low temperature over night, and after the mixture had been partly churned. The acetylmethylcarbinol content increased somewhat during the holding period. The results when aerated or modified aerated butter culture was added to sweet cream were similar to those when regular culture was employed, except that no increases in diacetyl were noted immediately after mixing, and the subsequent increases, while quite significant in actual amounts, were small on a percentage basis because of the relatively large amounts of diacetyl already supplied by these cultures. It was not possible to note a close relationship between the diacetyl contents of the butter cultures added to the cream and those of the resulting butter. Aerated or modified aerated cultures, as compared with equal percentages of regular cultures, yielded butter having higher diacetyl contents, but these values were really much lower than they would have been if a proportionality existed between the diacetyl contents of the cultures and the butter. On the average, 8.8 per cent of the diacetyl and 4.5 per cent of the acetylmethylcarbinol plus diacetyl in the churning mixture were retained in the butter.

Diacetyl in Cold-Stored Butters

1. Acetyl methyl carbinol and diacetyl are present in New Zealand butters made from slightly ripened cream.2. Most of the carbinol + diacetyl found in such butters would appear to have been added with the starter to the cream, rather than developed during the customary mild ripening process.3. Little change in the natural carbinol + diacetyl content of butter occurs during cold storage at 14—17° F. for more than 6 months.4. Larger amounts of diacetyl (4 p.p.m.) added to butters made from cream with and without the use of starter, show considerable losses after several months' cold storage. The losses are of the same order, but, with the butters, made with starter, part of the diacetyl has merely been reduced toits precursor (carbinol) form.