Formation Of Volatile Acids Research Articles

Understanding the effect of fermentation time on physicochemical characteristics, sensory attributes, and volatile compounds in green tea kombucha

Kombuchas are a trend in the fermented beverage field and the effect of fermentation time on their characteristics is necessary to better understand the process, mainly concerning volatile compounds, which are scarce information in the current literature. Thus, the present work aimed to evaluate the features of green tea kombucha during fermentation, monitoring the changes in pH, acidity, turbidity, polyphenols, ethanol, acetic acid, volatile compounds, and sensory profile and acceptance up to 14 days of fermentation. Kombuchas’ pH and acidity decreased through time as expected, but after 4 days of fermentation, the beverage exceeded the Brazilian legal limits of acidity (130 mEq/L) and produced more than 0.5% AVB, which labels the beverage as alcoholic. Total polyphenols and condensed tannins content enhanced until the seventh day of fermentation and remained constant. Fermentation highly impacted the aroma of the infusion with a high formation of volatile acids, such as alcohols, esters, and ketones. Aldehydes were degraded during the bioprocess. Sensory characterization of kombucha showed that fermentation of 4 days increased perceived turbidity; vinegar, citric fruit, acid, and alcoholic aroma; and produced the beverage with sour, bitter, and vinegar flavor. Thus, the fermentation time of kombuchas must be controlled as they rapidly change and impact on the physicochemical parameters and sensory profile of the beverage can be negative.

Potentiality of municipal sludge for biological gas production at Soba Station South of Khartoum (Sudan)

Potentiality of municipal sludge for biological gas production at Soba Station South of Khartoum (Sudan)

Effect of substrate concentrations on methane and hydrogen biogas production by anaerobic digestion of a cassava starch-based polymer

This study aims to evaluate the two-phase anaerobic digestion process of a cassava starch-based polymer, determining the ideal organic load to obtain the best results in terms of removal of solids and production of methane and hydrogen. Two reactors were used: one with an agitation and mixing system for the acidogenic phase, and the other was a tubular reactor for the methanogenic phase, both with ascending flow and semi-continuous feeding, with the effluent from the acidogenic reactor conducted from the methanogenic reactor. The loads were defined as concentrations of 8, 10, 12, and 14 g L−1 (on a wet basis), having HRT of 5 days for the acidogenic reactor and 20 days for the methanogenic. The analysis of the results showed that the concentration of 10 g L−1 had the best results for hydrogen and methane production in acidogenic and methanogenic phases, presenting 19.9 mL gVS-1 and 249.1 mL gVS−1, respectively. This treatment also showed the highest levels of gases in the biogas (43.2 % hydrogen in the acidogenic phase, and 76.6 % methane in the methanogenic phase). In addition, it showed the highest volatile solid removal means, reaching 84.0 % in the methanogenic phase. Thus, the anaerobic biodigestion process in two phases for the degradation of the polymer based on cassava starch presents technical feasibility, with high methane and hydrogen production; and concentrations above 10 g L−1, under the test conditions, cause destabilization in the reactors by the great formation of volatile acids and consequent reduction in the stability of microbiological cultures.

A rotational drum fermentation system with water flushing for enhancing hydrolysis and acidification of solid organic wastes

In this work, fresh soybean meal was used as the substrate for both batch and continuous experiments in a rotational drum fermentation (RDF) system to characterize the acidogenic process of solid organic waste degradation at high unionized volatile acid (U-VA) level and evaluate the effect of water flushing on the acidogenic performance. The experiments were conducted under mesophilic condition with a reaction time of 20 days. The results of the batch experiment showed that U-VA had a growing adverse effect on the volatile acid (VA) production and hydrolysis of the substrate as the initially added U-VA concentration increased (0, 5, 15, 25 g/L). VA formation deteriorated drastically when the initial U-VA concentration exceeded 5 g/L. VS degradation ratios decreased from 43.8% to 7.3%, and the hydrolysis rate constants varied between 28.8 and 3.8 × 10 −3/d in response to the initial U-VA concentration. In the continuous experiment, two cascade process configurations (CP1 and CP2) without and with VA removal by water flushing, respectively, were developed. The results showed that the hydrolysis rate constants and VS degradation ratios were 13.1 × 10 −3/d and 23%, respectively, in CP2, while only 9.1 × 10 −3/d and 16.7% in CP2. Compared to CP1, the VA spectrum varied little in CP2 with water flushing. It suggested that the higher U-VA level had a significant inhibition on the acidogenic process of solid organic waste degradation, and the VA removal by water flushing improved the acidogenic performance.

Quality and sensory acceptance of fish sauce partially substituting sodium chloride or natural salt with potassium chloride during the fermentation process

SummaryFish sauce was prepared with sodium chloride or natural salt partially replaced by potassium chloride at three ratios, 90 : 10, 75 : 25 and 60 : 40. Volatile acids were collected by steam distillation under reduced pressure and measured. The sensory property of the products was evaluated. The amino acid content was also measured. Most of the volatile acids in all the samples with added KCl were higher than in the controls, suggesting a role for KCl in the formation of volatile acids in fish sauce manufacture. Sensory evaluation showed slight differences in odour between the samples with added KCl and the controls, but the differences did not affect the acceptability of the product. However, acceptance of taste terminated at a 75 : 25 NaCl or natural salt : KCl ratio. Almost all the amino acids in the control and in the fish sauces with added KCl were comparable to those of commercial fish sauce. Partial substitution of NaCl or natural salt with KCl up to a ratio of 75 : 25 seems feasible.

Validation of the rancimat test for the assessment of the relative stability of fish oils

AbstractThe induction periods for the peroxidation of various fish oils at 55–90°C were studied by the Rancimat test. The natural logarithms of the induction periods varied linearly with respect to temperature, with a mean coefficient of −7.5×10−2°C−1, which was significantly different from that reported for vegetable oils. The activation energy for the formation of volatile acids had a mean value of 38.9 kJ/mol and was independent of the fish oil source. Peroxide formation under Rancimat test conditions followed first‐order kinetics. The same kinetics were followed under Schaal Oven test conditions (forced‐air oven, 60°C). On the basis of the results obtained, the Rancimat test appears to be useful in determining the relative stabilities of fish oils without the change in peroxide decomposition kinetics that may occur at elevated temperatures.

Upflow Anaerobic Sludge Digestion in a Phase Separation System

This paper aims to expand the knowledge about methods for improving the rate of solids hydrolysis, volatile acid formation and methane gas production. It studies the effects of phase separation and operational modes on the performance of the process. Two systems were investigated. The two-phase system consisted of a CSTR acid-phase digester and an upflow methane-phase digester, the one-phase system comprised of an upflow anaerobic digester. In order to provide optimal contact conditions and recycle liberated indigenous enzymes or cell biomass fractions, continuous recycling of the effluent sludges to the sludge bed of the reactor was used. In general, the nonbiodegradable portion of the substrates contained in the mixed sludges was found to be about 45% on the basis of TVS. The TVS reduction of the two-phase system was 53%, this is higher than in the one-phase system. Methane production rate and methane content were 0.351 l/g TVS added and 66.6%, respectively.

Formation of volatile acids in the various stages of fish sauce fermentation.

The rate of production of volatile acids present in the intermediate products at 3, 4, 10 and 15 months of fermentation of commercial Patis obtained in the Philippines and fish sauce of small scale preparation made in the laboratry was investigated. Also, an attempt to clarify the origin of these acids was conducted. Results of these experiments showed that concentrations of low molcular volatile acids were found to be higher in gut than in the whole and in flesh of fish in the both 24hours and 1 week incubations. It was also found that acids increased quantitatively and qualitatively with the progress of fermentation. It seems that almost all the acids identified in the sauce were formed within 3 months of fermentation. In this study, when fish was incubated without the addition of salt, most of the acids found reached very high levels compared with that in the fish incubated with the addition of salt. This might suggest involvement of bacterial action in the production of volatile acids.

Total volatile acids content as a quality index of irradiated hake ( Merluccius merluccius hubbsii) fillets

Irradiation of hake ( Merluccius merluccius hubbsii) fillets with 500 krad (5 k Gy) of Co 60 gamma rays caused a delay in the formation of volatile acids during storage under refrigeration at 4–5°C. Loss in organoleptic acceptability could be correlated with the increase in volatile acids both in the unirradiated and irradiated fish stored at 4–5°C, suggesting that the volatile acids number (VAN) can be a useful tool for the quality evaluation of hake fillets.

Anaerobic formation of volatile acids in a chemostat

If anaerobic digestion of waste can be performed as a two-step fermentation it becomes possible to optimize the separate steps. As the CH4 formation is assumed to be the slower step and the step more sensitive to substrate composition, an improvement of the overall process could be achieved by control of the effluent from the preceding step, in which volatile acids are formed. In this paper it is demonstrated that the composition of volatile acids from a chemostat varies to a great extent with dilution rate, so that, if an optimal composition of volatile acids exists for the CH4-forming step, it might be obtained by proper choice of dilution rate. The best substrate for CH4-formations is discussed.

Effects of Process Parameters on Formation of Volatile Acids and Free Fatty Acids in Quick-Ripened Blue Cheese1,2

A Blue cheese of desirable quality was produced by a modification of a quick-ripening procedure. This technique involves direct inoculation of mold into milk prior to addition of rennet and rapid curing of the particulate cheese curd in place of hooping, pressing, and aging. The curing room is at a temperature of 17C and a relative humidity of 95%. Ripening is in 7 days in contrast to curing 90 days to 1 yr by conventional processes. The research was to evaluate and refine the quick-ripening process. Variables included salting, temperature of cooking, and curing of curd, homogenization and pasteurization of the milk, and addition of a commercial lipase. During the curing of the cheese, pH and volatile acidity were determined daily. Upon completion of curing, free fatty acids were separated and quantitated by gas liquid chromatography. Sensory evaluation was made on all batches of cheese. 1) Salting times and temperature of curing were critical for development of flavor and control of contamination. 2) Homogenization and pasteurization were necessary for development of clean, full flavor. 3) Addition of a lipase did not aid in development of flavor. 4) Cooking the cheese curd strengthened the cheese particles, reduced curd loss, and permitted faster drainage. Cheese comparable or superior to commercial Blue cheese could be produced by modifications of the quick-ripening process.

Induction of Malo-Lactic Fermentation by Inoculation of Must and Wine with Bacteria

Two strains of lactic acid bacleria, previously isolated from California wines, were used to induce the malo-lactic fermentation in must and wine. Under the condition described, the malo-lactic fermentation was independent of the stage of the alcoholic fermentation at which the bacterial inoculations were made. The malolactic fermentation was much more rapid with ML 34 (<i>Leuconostoc</i> sp.) than with ML 30 (<i>Lactobacillus</i> sp.) The conversion of malic acid to lactic acid was made to occur in both dry wine and in must in the presence of SO₂ by the use of a large inoculum of bacteria. In no instances was the malo-lactic fermentation accompanied by any detrimental effect to the wines. Slight but chemically detectable increases of volatile acid occurred with the malolactic fermentation. There was no further increase in volatile acidity after the end of the malo-lactic fermentation, and fining was thus not necessary to halt further volatile acid formation.

Changes in Polybutadiene Rubber under Various Conditions of Aging

Abstract 1. The systematic relations of the oxidation of SKB under the action of heat, light, and ionizing radiation are considered and it is shown that the formation of a series of oxygen-containing products takes place (hydroperoxides, alcohols, aldehydes, ketones, acids, ethers, and esters). The general tendency for formation of these compounds was clarified for each separate case. 2. The behavior of double bonds of various configurations (1,2 and cis and trans 1,4) reveals differences in reactivity, namely: in the thermal, light, and radiation reactions, a decrease of the number of double bonds in the 1,2 position takes place, in general this is due to crosslinking and formation of volatile acids, but in the radiation reaction it is also due to hydrogenation. The increased rate of the decrease of the number of cis 1,4-bonds is in all cases interpreted as evidence of isomerization to the trans-configuration. It was shown that migration of 1,4 double bonds along the chain towards the tertiary carbon atoms and formation of conjugated double bonds (band at 1595 cm−1) takes place. 3. A decrease of the number of double bonds in the backbone (cis and trans 1,4) takes place that is mainly due to the formation of oxygen-containing compounds. Therefore, the quantitative investigation of this process can give an idea of the level of oxidative degradation. 4. The increase of the total absorption in the region 1400 to 750 cm−1 is connected with crosslinking. This, together with other existing methods (investigation of equilibrium swelling and stress relaxation) can be used for the estimation of the degree of crosslinking.

Formation of Volatile Acids in Black Tea

The determination of volatile acids (VA) in black tea was carried out by the titration for the distillate of black tea with N/20 NaOH.The weak or bad smelling black teas showed a tendency to contain much VA. On the course of black tea manufacture, VA increased considerably in the rolling and the fermentation process. When the operational conditions were changed, VA more increased as the longer time and the higher temperature in the fermentation and the drying.The above mentioned results resembled to those on the formation of volatile carbonyl compounds. When tea leaves were ground with amino acid or aldehyde and fermented, VA of the resulting black tea increased, but the boiled tea leaves after the fermentation could not produce VA from amino acid or aldehyde.It is, therefore, supposed that the formation mechanism of a part of VA in black tea aroma was as follows: amino acids and unknown precursors→oxidation by some enzymealdehydes→VA

Kaffircorn malting and brewing studies. II.—Studies on the microbiology of Kaffir beer

AbstractThe three main microbiological conversions in the production of kaffir beer have been studied, viz.: the souring of the mash by lactic acid bacteria, the alcoholic fermentation of the wort by a variety of yeasts generally present on the malt used in the conversion and, finally, the spoilage due to volatile acid formation. It was found that in breweries where no temperature control was practised during souring, a very heterogeneous lactic acid microflora developed. Eight species were recognized. In the subsequent alcoholic fermentation twenty different yeast species were isolated from beers. Saccharomyces cerevisiae, Candida krusei and Kloeckera apiculata were found to be the predominant species. The spoilage due to excessive acetic acid formation was found to be caused by the development of the common malt and beer Acetobacter species.

The determination of the volatile fatty acids formed during the fermentation of grass/water mixtures

1. The use of the technique of gas-partition chromatography in the investigation of the formation of volatile acids in minced grass/water slurries is discussed.2. Slurries kept anaerobically at 17, 37 and 62° for 13 weeks have been examined, and the amounts of the different volatile acids formed have been estimated. It has been noted that butyric acid forms most readily in the slurry at 37°, while in aerated slurries at 17°, the formation of volatile fatty acids is more speedy than under anaerobic conditions.3. Only acetic, propionic and butyric acids have been noted so far, and the highest concentrations of the acids observed in any slurry were 5, 1·25 and 4% respectively.

The Formation of Volatile Acids in Milk by High-Temperature Heat Treatment

The Formation of Volatile Acids in Milk by High-Temperature Heat Treatment

Acid Metabolism of Wine Yeast. I. The Relation of Volatile Acid Formation to Alcoholic Fermentation

Acid Metabolism of Wine Yeast. I. The Relation of Volatile Acid Formation to Alcoholic Fermentation

The effect of the addition of various materials and bacterial cultures to grass silage at the time of making on the subsequent bacterial and chemical changes

The investigations previously described (1) have demonstrated that the changes occurring in the early stages of silage fermentation result in simultaneous development of acidity and degradation of proteins. There seems little reason to doubt that the lactobacilli play an effective part in the former by virtue of their formation of lactic acid. Contributions to proteolysis are undoubtedly made by various groups of bacteria, and in the later stages of ripening the spore-forming anaerobes, if numerous, will cause extensive protein breakdown and formation of volatile acids, especially butyric acid. The growth of the latter group of bacteria is greatly affected by thepH of the silage, for at values below about 4·0 the only group capable of anything like active multiplication is the lactobacilli. In fact the A.I.V. method of making silage consists in the addition of mineral acids at the commencement in quantities sufficient to reduce thepH to approximately 3·5. The production of good silage with a minimum loss of feeding value, low proteolysis and the presence of only small quantities of butyric acid may therefore be regarded as depending on the formation of sufficient acid in the earlier stages to retard the activities of the obligate anaerobes and proteolytic bacteria in the later stages.