EFFECTS OF YEAST,FERMENTATION TIME,AND PRESERVATION METHODS ON TARHANA

The physicochemical properties of tarhana soup produced with different dough treatments, fermentation times, and preservation methods were examined. Tarhana doughs were prepared with yogurt (control) or baker's yeast (Saccharomyces cerevisiae) and fermented for 3 days. Samples were taken at 24, 48, and 72 hr. Samples were then preserved via one of four methods: sun dried, dried in the shade, vacumn dried, and frozen. Frozen samples produced lower organic acid levels after 72 hr of fermentation in both control (0.68 g/100 g) and yeast (0.61 g/100 g) applications than samples that were dried (0.94 g/100 g control samples; 0.81 g/100 g samples with yeast). Increasing fermentation time resulted in a significant effect on the formation of organic acid in the tarhana (p < .01). At 72 hr of fermentation, total acidity increased 11%, 17%, and 23% for tarhana samples vacumn-dried, sun-dried, and dried in the shade, respectively. Preservation methods also affected the moisture, ash, crude protein, total acidity, pH, salt, fat, reducing sugar levels, and the sensory assestment of tarhana soup (p < .01). Sensory characteristics were not significantly affected by baker's yeast in any of the preservation methods used (p > .01). However, sensory scores for tarhana prepared from the samples dried in a sheltered area showed a reduction in color desireablilty as the fermentation time increased. The soup prepared from frozen tarhana (72 hr fermentation, with yeast) had the highest scores with respect to color, mouth feel, flavor, and overall acceptability. Vacuum-dried samples' scores in these areas were also high in comparison to the two other drying methods.     

Inhibition of alcoholic fermentation by substrate and ethanol

The effect of ethanol and sugars on rates of fermentation was studied. We used a strain of Canadida pseudotropicalis. The specific rate of fermentation was determined by using the Warburg manometer. The effect of ethanol was formulated as an exponential function of ethanol concentration, but the empirical constant was different when glucose or lactose was used as a substrate. The effects of both ethanol and substrate were formulated. It was demonstrate that when lactose and glucose were present in the medium with a small amount of alcohol, a synergistic effect on the rate of fermentation appeard. This phenomenon considerably limits the rate of fermentation.     

用于红霉素生产的500m3生物反应器的理性设计

红霉素(erythromycin)是由绛红色糖多胞菌(Saccharopolyspora erythraea)发酵生产的次级代谢产物,其生产水平不仅受发酵工艺的影响,也受反应器结构影响。为解决红霉素发酵过程放大问题,本研究采用时间常数法和计算流体力学(computational fluid dynamics,CFD)数值模拟验证相结合的方法设计了500m³超大规模红霉素耗氧发酵生物反应器。首先,通过对50L反应器红霉素发酵过程研究,发现溶氧是关键性限制因素,通过氧消耗速率(oxygen uptake rate,OUR)等参数分析计算得到设备的氧供应时间常数t_mt需小于6.25s。然后,基于时间常数法和经验关联式理性设计500m³反应器搅拌桨叶组合方式,即底层BDT8桨叶+两层MSX4桨叶的搅拌桨组合,并通过经验公式及CFD方法对设计结果进行了模拟验证。两种验证方法结果均表明500m³反应器采取底层BDT8桨叶+两层MSX4桨叶的组合方式时设备的氧供应时间常数小于6.25s,且反应器内流场特性(如持气率、剪切率和速度矢量等)均能满足红霉素大规模发酵的需要。经实际发酵验证,设计的生物反应器能够满足红霉素的工业规模发酵应用。     

SILICON UPTAKE BY ALGAE WITH NO KNOWN Si REQUIREMENT. II. STRONG pH DEPENDENCE OF UPTAKE KINETIC PARAMETERS IN PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE)1

Silicon uptake kinetics of the diatom Phaeodactylum tricornutum (Bohlin) were examined at pH 8.8 ± 0.1 and pH 9.1 ± 0.1. Uptake follows hyperbolic saturation kinetics at both pH's, but at the higher pH the half-saturation constant for uptake is 11.8 μM, as opposed to 54.8 μM at the lower pH. When the uptake rate is examined as a function of the calculated concentration of the monovalent conjugate base, SiO(OH)₃^?, the half-saturation constant for uptake is 6.6 μM at either pH.     

Citric acid production from glucose. I. Growth and excretion kinetics in a stirred fermentor

The growth and citric acid production kinetics of Saccharomycopsis lipolytica on glucose are investigated in an aerated stirred fermentor. Cellular growth first proceeds exponentially until exhaustion of ammonia in the fermentation medium. Cells then continue to grow at a reduced rate with a concomitant decrease in intracellular nitrogen content. Citric and isocitric acid production starts at the end of the growth phase. During about 80 hr excretion proceeds at a constant rate of 0.7 g/liter/hr for citric acid and 0.1 g/liter/hr for isocitric acid. The final citric and isocitric acid concentrations are 95 and 10g/liter, respectively. During acid excretion cellular respiration accounts for 60 and 35% of consumed oxygen and glucose. Both acid and CO₂ production rates follow a Michaelis–Menten-type dependence on oxygen concentration with Michaelis–Menten constants of 0.9 and 0.15 mg/liter for acid and CO₂ productions, respectively.     

Effect of aggregation on the optical rotatory dispersion of poly(α,L-glutamic acid)

Light-scattering measurements show that poly(α,L -glutamic acid) (PGA) is strongly aggregated at the low pH's (4.0–4.3) usually used to measure the mean residue rotation at the trough, [R′]₂₃₃, and that [R′]₂₃₃ becomes more negative with aggregation. Concurrent weight-average molecular weight measurements by light-scattering and [R′]₂₃₃ measurements by optical rotatory dispersion as a function of pH show that a maximum negative value for [R′]₂₃₃ (unaffected by aggregation) is obtained at higher pH's (4.53–4.82). Precautions should be taken to insure that the Na-PGA sample used as standard does not aggregate at the low pH's required for its complete conversion to the helical form. An Na-PGA sample meeting the above requirements gives [R′]₂₃₃ of ?14,600° ± 1.5% over the pH range 4.53–4.82 in 0.05M NaCl.     

The Effects of pH,Buffers, Bile and Bile Acids on Excystation of Sporozoites of Various Eimeria Species*

SYNOPSIS. Oocysts of Eimeria bovis were found to undergo excystation when subjected at 39 C to a pretreatment consisting of exposure for 24 hr to CO₂ and air (50–50), and a treatment for 7 hr with a mixture of bile and trypsin. At pH's of 6.0 thru 10.0 with tris-maleate buffer, excystation occurred over the entire range of pH tested, with the highest levels at pH 7.5-8.5. No adverse or inhibitive effect on excystation or the viability of the sporozoites was observed. Disintegration of sporozoites occurred within the sporocysts of intact oocysts at each of the pH levels studied when boric acid-borax, ammediol, and glycine-sodium hydroxide buffers were used in the treatment medium. Phosphate buffer inhibited excystation when used in the excysting medium. Excystation occurred at levels above 90% in all dilutions of taurocholic, glycocholic, glycotaurocholic, and cholic acids included in the study (0.5-10.0%) except for the 10% and 5% dilutions of cholic acid and the 10% dilution of glycotaurocholic acid. In the latter 3 dilutions, sporozoites within the sporocysts of intact oocysts disintegrated. Excystation levels above 90% were observed in the 50% and 10% dilutions of fresh bovine bile, and in the 5% dilution of lyophilized bovine bile. Lower levels of excystation occurred in greater dilutions of both kinds of bile. No excystation occurred when any of the bile acids, fresh bovine bile or lyophilized bile were used without trypsin, except for fresh bile that contained a heavy suspension of bacteria and fungi. In a medium containing trypsin and heat-treated bile, heat-treated bile acids, or no bile, 2.5–8% of the oocysts excysted. The findings indicate that satisfactory excystation can be obtained with a treatment medium containing tris-maleate at pH 7.5–8.5, 0.25% trypsin, and 1% of one of the bile acids.     

Growth and Toxigenesis of the Chrysomonad Prymnesium parvum as a Function of Salinity*

SYNOPSIS The euryhaline chrysomonad Prymnesium parvum (Carter) was grown in artificial (ASW) and natural sea water (NSW) media at salinities 1.3-33.3 ‰, and constant illumination. Low salinities (< 10‰) increased the doubling time (DT) and induced higher levels of protein and nucleic acids. DT was lowest for cells in ASW at 25 ‰ and NSW 17.9 ‰. The protein content was more variable. RNA content was lowest for cells at ca. 10 ‰. The DNA content was lowest for cells in 10‰ ASW and 11‰ NSW. Generally, the cells grew faster in NSW but had less protein and RNA than cells in ASW. The highest hemolytic content was in cells grown at 22.8 ‰ ASW or NSW. Glycerol enhanced growth rate and toxin synthesis within 24 hr of addition to the cells. Hemolysis was inhibited by high pH's. A membrane fraction containing ca. 20% of the hemolysin was isolated by density gradient centrifugation.     

Improved homo <Emphasis Type="SmallCaps">l</Emphasis>-lactic acid fermentation from xylose by abolishment of the phosphoketolase pathway and enhancement of the pentose phosphate pathway in genetically modified xylose-assimilating <Emphasis Type="Italic">Lactococcus lactis</Emphasis>

In order to achieve efficient homo L-lactic acid fermentation from xylose, we first carried out addition of xylose assimilation ability to Lactococcus lactis IL 1403 by introducing a plasmid carrying the xylRAB genes from L. lactis IO-1 (pXylRAB). Then modification of xylose assimilation pathway was carried out. L. lactis has two pathways for xylose assimilation called the phosphoketolase pathway (PK pathway) that produces both lactic acid and acetic acid and the pentose phosphate pathway (PP pathway) that produces only lactic acid as a final product. Thus a mutant strain that disrupted its phosphokeolase gene (ptk) was constructed. The Δptk mutant harboring pXylRAB lacked the PK pathway and produced predominantly lactic acid from xylose via the PP pathway, although its fermentation rate slightly decreased. Further introduction of the transketolase gene (tkt) to disrupted ptk locus led restoration of fermentation rate and this was attributed to enhancement of the PP pathway. As a result, ptk::tkt strain harboring pXylRAB produced 50.1 g/l of L-lactic acid from xylose with a high optical purity of 99.6% and a high yield of 1.58 (moles per mole xylose consumed) that is close to theoretical value of 1.67 from xylose.     

Hydrolysis and acidification of waste-activated sludge in the presence of biosurfactant rhamnolipid: effect of pH

In this investigation, the effect of pH (4.0–11.0) on waste-activated sludge (WAS) hydrolysis and acidification in the presence of a biosurfactant rhamnolipid (RL) were studied. The results showed that the hydrolysis and acidification of WAS in the presence of RL at alkaline pH values were more efficient than that at acidic and near-neutral pH values. After 6 h of hydrolysis, the soluble protein and carbohydrate were 1,654.7 and 675.9 mg/L (pH 11.0), and 825.6 and 376.0 mg/L (pH 7.0), whereas the values were only 315.0 and 84.0 mg/L at pH 4.0 and 164.1 and 32.0 mg/L for the blank, respectively. After 2 or 3 days of fermentation, the accumulated short-chain fatty acids (SCFAs) reached the highest and then decreased with a further increase in time at all investigated pH values. The analysis of SCFA compositions showed that acetic, propionic, and iso-valeric acids were the three main products at any pH value. A higher pH contributed to a greater proportion of acetic acid and a lesser proportion of iso-valeric acid; a lower pH resulted in a greater proportion of iso-valeric and lesser proportion of acetic acid in the initial fermentation. The proportions of acetic acid for the system with biosurfactant RL addition were 16.65, 36.33, and 62.94 %, respectively, at pH 4.0, 7.0, and 11.0 after 1 day. Correspondingly, the proportions were 40.34, 12.60, and 11.01 % for iso-valeric acid.     

The impact of acetate metabolism on yeast fermentative performance and wine quality: reduction of volatile acidity of grape musts and wines

Acetic acid is the main component of the volatile acidity of grape musts and wines. It can be formed as a by-product of alcoholic fermentation or as a product of the metabolism of acetic and lactic acid bacteria, which can metabolize residual sugars to increase volatile acidity. Acetic acid has a negative impact on yeast fermentative performance and affects the quality of certain types of wine when present above a given concentration. In this mini-review, we present an overview of fermentation conditions and grape-must composition favoring acetic acid formation, as well the metabolic pathways leading to its formation and degradation by yeast. The negative effect of acetic acid on the fermentative performance of Saccharomyces cerevisiae will also be covered, including its role as a physiological inducer of apoptosis. Finally, currently available wine deacidification processes and new proposed solutions based on zymological deacidification by select S. cerevisiae strains will be discussed.     

Kinetics of polysaccharide B-1459 fermentation

Polysaccharide gum was made by fermentation with Xanthomonas campestris NRRL B-1459 in a medium of glucose, minerals, and distillers' solubles. The effect of distillers' solubles on growth rate can be described by the familiar saturation equation. Although a quasistoichiometric relationship was observed between nitrogen utilization and growth, total nitrogen supply was not growth limiting, nor was polymer formation growth associated. Cell growth primarily took place in the early part of the fermentation; polysaccharide biosynthesis occurred throughout the fermentation. Glucose was converted to polysaccharide at a fairly constant yield, which was 70–80% of glucose consumed, under optimum conditions. The kinetic patterns observed indicate that multistage continuous fermentation will be suitable for polysaccharide production.     

Production of Calcium Gluconate by Penicillium chrysogenum in Submerged Culture

The waste mycelium of Penicillium chrysogenum HA-10 (obtained at the end of penicillin fermentation), or a 24-hr-old freshly grown vegetative inoculum of this organism, was found to utilize glucose for the production of calcium gluconate by submerged fermentation in shake flasks. After 72 to 96 hr of fermentation at 24 C, 90 to 95% of the reducing sugar from the 15% glucose medium was converted to calcium gluconate. Reuse of the mycelium for successive experiments reduced the fermentation period to 72 hr or less because of an enhancement of glucose utilization. Ten successive batches of 15% glucose medium were fermented by the reuse method. Fermentation media containing up to 30% glucose could be used, provided boric acid was added to prevent the precipitation of calcium gluconate formed. We found that 30% hydrol (a by-product of glucose manufacture containing 50 to 55% reducing sugar), when used in place of glucose in the fermentation medium, inhibited the rate of glucose utilization. However, this effect was partially reversed by pretreatment of hydrol with 2 to 4% activated charcoal before addition to the fermentation medium.     

Production of Candida utilis protein from peat extracts

Sphagnum peat extracts or hydrolysates have been obtained and used as a culture medium for the production of Candida utilis biomass as single cell proteins. Acid hydrolysis of ground peat (4–60 mesh) in an autoclave operated under a set of conditions for acid strength (0.3-1.5 (v/v) H₂SO₄), holding time (1–4 hr), temperature (100–165°C), and weight ratio of dry peat to solution (3.3–16.7 g dry peat/100 g solution) yielded carbohydrate-rich extracts of different concentrations (1–34g/liter). The best yield (mg total carbohydrate/g dry peat) was obtained for a holding time of I hr and a temperature of 152°C. Low peat concentratio (4.1 g dry peat/100 g solution)resulted in high yield(280mg total carbohydrate/gdry peat) with a corresponding low carbohydrate content in hydrolysate (13 g/liter), while a lower yield with a higher carbohydrate content (34 g/liter)in hydrolysate were found when increasing peat concentration (16.7 g dry peat/100 g solution). Shake-fladk experiments using peat hydrolysates as the culture medium together with NH₄OH (～4.8 g/liter) and K₂HPO₄(5 g/liter) as nitrogen and phosphate supplement, respectively, gave a maximum biomass concentration of 7.5 g/liter after 60 hr at 30°C and 200rpm. Batch cultivation in a fermentor under controlled conditions for aeration (4.2 liter/min), agitation (500rpm), temperature (30°C), and pH (5.0) produced a maximum biomass of 10 g/liter after 20 hr with a specific growth rate of 0.13 hr^?1. For the continuous cultivation, a maximal biomass productivity of 1.24 g/gliter-he was obtained at a dilution rate of 0.125 hr ^?1. Monod's equation's equation has been used for the estimation of the coefficients μ_Max, K_s, and Y. It was found that the yield coefficient Y is not constant during the progress of batch cultivation.     

Glutamine Production by Coupling with Energy Transfer: Employing Yeast Cells and Gluconobacter Glutamine Synthetase

A glutamine production process was established by combining alcoholic fermentation of baker's yeast cells with glutamine synthetase from the bacterium Gluconobacter suboxydans. The maximum amount of glutamine formed under optimum conditions was about 20 mM in 3 hr with 80% yield based on glutamate, substrate. The fermentation proceeded in two steps: the accumulation of energy in a form of fructose 1,6-diphosphate (FDP) by yeast fermentation of sugar based on the Harden-Young effect and the fermentation of FDP coupled with glutamine synthetase reaction (an endergonic reaction) through an ATP-ADP system. The following factors were found to be important: (a) the ratio of the activities of yeast fermentation of sugar and glutamine synthetase, (b) effect of contaminating enzyme(s) in glutamine synthetase preparation, and (c) enzymatic properties of glutamine synthetase.     

Utilization of carbohydrates by Thermomonospora sp. Grown on glucose,cellobiose, and cellulose

Thermomonospora sp. was grown on glucose, cellobiose, and in order to study its growth characteristics with different carbohydrate substrates and to assess the validity of some of the assumptions made in a previously proposed model for the cellulose fermentation with this microorganism. It was observed that the nitrogen and protein contents of the cells are essentially constant during the fermentation and independent of the carbon source when glucose or cellobiose are utilized. Under oxygen starvation conditions it was shown that unidentification organic compound(s) accumulate(s) in the culture broth. Culture fluorescence was shown to be an excellent variable for monitoring and control of the fermentation process. This microorganism showed a preference for crystalline cellulose (Avicel) as substrate although it grows readily on a more amorphous cellulose (Solka Floc). The production of extra cellular protein is shown to be growth related. Data were obtained confirming the decrease in the number of active adsorption sites as the cause for the decrease in the cellulose digestion rate. It is suggested that a future model should account for the time change of surface characteristics of the cellulose particles.     

Metabolic engineering of <Emphasis Type="Italic">Rhizopus oryzae</Emphasis> for the production of platform chemicals

Rhizopus oryzae is a filamentous fungus belonging to the Zygomycetes. It is among others known for its ability to produce the sustainable platform chemicals l-(+)-lactic acid, fumaric acid, and ethanol. During glycolysis, all fermentable carbon sources are metabolized to pyruvate and subsequently distributed over the pathways leading to the formation of these products. These platform chemicals are produced in high yields on a wide range of carbon sources. The yields are in excess of 85 % of the theoretical yield for l-(+)-lactic acid and ethanol and over 65 % for fumaric acid. The study and optimization of the metabolic pathways involved in the production of these compounds requires well-developed metabolic engineering tools and knowledge of the genetic makeup of this organism. This review focuses on the current metabolic engineering techniques available for R. oryzae and their application on the metabolic pathways of the main fermentation products.     

Improved succinate production from galactose-rich feedstocks by engineered Escherichia coli under anaerobic conditions

It is of great economic interest to produce succinate from low-grade carbon sources, which can make it more economically competitive against petrochemical-based succinate. Galactose sugars constitute a significant fraction of the soluble carbohydrate in a meal from agricultural sources which is considered a low value or waste byproduct of oilseed processing. To improve the galactose utilization, the effect of galR and glk on sugars uptake was investigated by deactivation of each gene in three previously engineered host strains. As expected, glk plays an important role in glucose uptake, while, the effect of deactivation of galR is highly dependent on the strength of the downstream module (succinate production module). A new succinate producer FZ661T was constructed by enhancement of the succinate producing module and manipulation of the gal operon. The succinate productivity reached 4.57 g/L/hr when a mixed sugar feedstock was used as a carbon source in shake-flask fermentation, up to 812 mM succinate was accumulated in 80 hr in fed-batch fermentation. When SoyMolaGal hydrolysate was used as a carbon source, 628 mM (74 g/L) succinate was produced within 72 hr. In this study, we demonstrate that FZ661T can produce succinate quickly with relatively high yield, giving it the potential for industrial application.     

Oxygen requirement and energy relations of itaconic acid fermentation by Aspergillus terreus NRRL 1960

The effect of interrupting aeration on itaconic acid fermentation by A. terreus NRRL 1960 has been studied. Under the conditions used, stopping aeration for 5 min led to a complete cessation of itaconic acid production, which was only slowly restored after 24 h when aeration was resumed. After a 5-min break in aeration and in the presence of 0.1 mM cycloheximide no itaconic acid was formed even after 3 days. It seems that, upon oxygen shortage, a rapid destruction of the itaconic-acid-producing mechanism takes place, which is restored only aerobically in a slow process involving protein synthesis. Itaconic acid fermentation is also effectively stopped by metabolic inhibitors of ATP formation, pointing to the need for biochemical energy in maintaining the fermentation. ATP is possibly needed to maintain a proper physiological (i.e. near neutral) pH inside the cells, counteracting the acid produced in the fermentation process and the low external pH (below 2.0). Inhibitors of plasma membrane ATPase have no effect on itaconic acid fermentation. This indicates that the plasma membrane might be impermeable to H⁺ and that ATP might rather be involved in the transport of itaconic acid out of the cell. It is suggested that insufficient aeration may leads to insufficient production of ATP which, in turn, leads to damage of the metabolic machinery by acid produced in the fermentation process.     

A kinetic study of the lactic acid fermentation. Batch process at controlled pH. Reprinted from Journal of Biochemical and Microbiological Technology Engineering Vol. I, No. 4. Pages 393-412 (1959)

Kinetic data are needed to develop basic understanding of fermentation processes and to permit rational design of continuous fermentation processes. The kinetics of the fermentation of glucose to lactic acid have been studied at six constant pH levels between 4. 5 and 6.0 by measuring the instantaneous rates of bacterial growth and of lactic acid formation throughout each fermentation. It was found that the instantaneous rate of acid formation dP/dt, should be related to the instantaneous rate of bacterial growth dN/dt, and to the bacterial density N, throughout a fermentation at a given pH, by the expression when the constants alpha and beta are determined by the pH of the fermentation.