Formation Of Volatile Byproducts Research Articles

Separate hydrolysis and fermentation and simultaneous saccharification and fermentation methods in bioethanol production and formation of volatile by-products from selected corn cultivars

Corn (Zea mays L.) is a widely used raw material in the production of bioethanol. Creating new cultivars and applying appropriate fermentation techniques to increase production efficiency is still important for bioethanol producers. The purpose of the study presented here was to evaluate the correlation between differentiators of corn cultivars and fermentation methods in view of the efficiency of bioethanol production. The five selected cultivars differed by FAO (Food and Agriculture Organization) number, type of hybrid cultivar, and type of grain. The tested samples generally showed significant (p < 0.05) differences in starch contents. Ethanol fermentation was investigated using separate hydrolysis and fermentation (SHF) as well as simultaneous saccharification and fermentation (SSF) methods The SSF method proved the most effective for the production of bioethanol, regardless of cultivar. The greatest ethanol yield (p < 0.05) was achieved with the semiflint SM Hetman cultivar (81.23% theoretical value) under the SSF process. A negative correlation (p < 0.05) between starch content and ethanol yield was demonstrated. Chromatographic analysis of the raw spirits showed that lower levels of fermentation by-products were detected for the SSF method than for SHF.

Influence of various yeast strains and selected starchy raw materials on production of higher alcohols during the alcoholic fermentation process

The formation of volatile by-products during alcoholic fermentation is affected by many factors such as the type of yeast strain applied, technological parameters of the process and the raw material used as the main constituent of the fermentation medium. The influence of availability of sugars released by the plant polysaccharide hydrolysis on the concentration of higher alcohols during the fermentation process was analyzed. Significant differences in the starch hydrolysis dynamics for various raw materials, entailing changes in availability of sugars such as glucose, maltose, maltotriose and maltotetraose, are reported. The highest glucose concentration after the mashing process (93.8 ± 3.8 mg cm−3) was observed for the maize mash (as compared to that of the rye and amaranth mashes, 24.9 ± 0.9 and 46.9 ± 2.5 mg cm−3, respectively). The highest glucose content in the maize mash resulted in a significantly higher isobutanol and 2-methyl-1-butanol content at the initial stage of fermentation, irrespective of the yeast strain used (D-2 or As-4). The highest final total content of fusel alcohols (ca. 5,460 mg dm−3 EtOH, on average) was also found in the distillates produced from the maize mash. However, the concentration of higher alcohols in the rye and amaranth distillates was similar and reached the level of ca. 3,440 mg dm−3 EtOH, on average. It is shown that the polysaccharide hydrolysis rate, and hence the rate at which fermenting sugars are released, significantly affects the concentration of higher alcohols in the produced distillates.

Adhesion of yeast cells to different porous supports, stability of cell-carrier systems and formation of volatile by-products

The aim of our research was to study how the conditions of immobilization influence cell attachment to two different ceramic surfaces: hydroxylapatite and chamotte tablets. Three fermentative yeast strains, namely brewery TT, B4 (ale, lager) and distillery Bc15a strains belonging to Saccharomyces spp., and one strain of Debaryomyces occidentalis Y500/5 of weak fermentative nature, but with high amylolytic activity due to extracellular α-amylase and glucoamylase, were used in this study. Different media, including cell starvation, were applied for immobilization of yeast strains as well as different phases of cell growth. Immobilization of selected yeasts on a hydroxylapatite carrier was rather weak. However, when incubation of starved yeast cells was conducted in the minimal medium supplemented by calcium carbonate, the scale of immobilization after 24 h was higher, especially for the D. occidentalis strain. Adhesion to hydroxylapatite carriers in wort broth was of reversible character and better results of adhesion were observed in the case of another ceramic carrier-chamotte. The number of immobilized cells was about 106–107 per tablet and cell adhesion was stable during the whole fermentation process. The comparison of the volatile products that were formed during fermentation did not show any significant qualitative and quantitative differences between the free and the immobilized cells. This is the first time when a cheap, porous chamotte surface has been applied to yeast adhesion and fermentation processes.

Condensation cascades and methylgroup transfer reactions during the formation of arsane, methyl- and dimethylarsane by aqueous borohydride and (methyl) arsenates

The formation of volatile products during the reaction of As(III: ), As(V: ), MeAsO(OH)(2), and Me(2)AsO(OH) with aqueous NaBH(4) has been investigated, and the formation of arsanes, diarsanes, and triarsanes has been detected. The presence of triarsanes is reported here for the first time. Diarsanes and triarsanes are likely formed in condensation cascade reactions, whereas trimethylarsane arises via the transfer of a methyl group. The formation of volatile by-products is considerably reduced by increasing the acidity of the medium and the concentration of NaBH(4) or by the addition of thiols, such as cysteine. A reaction scheme is proposed which reconciles the evidence reported herein and elsewhere in the literature that is valid for both analytical (trace analysis) and non-analytical reaction conditions.

High-temperature alcoholic fermentation of whey using Kluyveromyces marxianus IMB3 yeast immobilized on delignified cellulosic material

A novel system for high-temperature alcoholic fermentation of whey is described. This system consists of Kluyveromyces marxianus yeast immobilized on delignified cellulosic material (DCM). The effect of pH, initial lactose concentration and temperature on the fermentation of a synthetic medium containing lactose was studied. Batch fermentations of whey were also carried out and the formation of volatile by-products was examined. The concentrations of higher alcohols were found to be in very low levels leading to a product of improved quality. The fermented whey had an improved characteristic aroma compared to unfermented whey. The possibility to use fermented whey as raw material for the production of a novel, low alcohol content drink was also investigated.

Etching Characteristics of WSi2 with Pulsed-Electron Cyclotron Resonance Plasma

Etching properties of WSi2 are investigated with pulsed-electron cyclotron resonance (ECR) plasma. A new type of charge-induced notch, which appears at an inside line, has been discovered in polycide etching. By comparing the notch properties to reactive ion etch (RIE) lag characteristics, the deposition of a conductive film on the sidewall is suggested as the origin of the electrons. The RIE-lag is improved with pulse plasma due to a reduced dissociation of reaction byproducts. The dissociation of byproducts produces a large amount of tungsten. The actual quantity depends on the duty ratio of the pulse modulation, and continuous discharge is the worst case. The formation of volatile byproducts with pulse plasma also effectively reduces RIE-lag. The volatile byproducts are formed during afterglow, which produces an electron temperature lower than the W–Cl bond strength.