Optimizing medium constituents and fermentation conditions for citric acid production from palmyra jaggery using response surface method

The quantitative effects of pH, temperature, time of fermentation, sugar concentration, nitrogen concentration and potassium ferrocyanide on citric acid production were investigated using a statistical experimental design. It was found that palmyra jaggery (sugar syrup from the palmyra palm) is a suitable substrate for increasing the yield of citric acid using Aspergillus niger MTCC 281 by submerged fermentation. Regression equations were used to model the fermentation in order to determine optimum fermentation conditions. Higher yields were obtained after optimizing media components and conditions of fermentation. Maximum citric acid production was obtained at pH 5.35, 29.76 °C, 5.7 days of fermentation with 221.66 g of substrate/l, 0.479 g of ammonium nitrate/l and 2.33 g of potassium ferrocyanide/l.     

Optimization of fermentation conditions for the production of ethanol from sago starch using response surface methodology

The quantitative effects of temperature, pH and time of fermentation were investigated on simultaneous saccharification and fermentation (SSF) of ethanol from sago starch with glucoamylase (AMG) and Zymomonas mobilis ZM4 using a Box–Wilson central composite design protocol. The SSF process was studied using free enzyme and free cells and it was found that with sago starch, maximum ethanol concentration of 70.68 g/l was obtained using a starch concentration of 140 g/l, which represents an ethanol yield of 97.08%. The optimum conditions for the above yield were found to be a temperature of 36.74 °C, pH of 5.02 and time of fermentation of 17 h. Thus by using the central composite design, it is possible to determine the accurate values of the fermentation parameters where maximum production of ethanol occurs.     

Kinetics of ethanol production by immobilized Kluyveromyces marxianus cells at varying sugar concentrations of Jerusalem artichoke juice

Summary Kinetics of ethanol fermentation at varying sugar concentrations of Jerusalem artichoke tuber extract has been studied using Kluyveromyces marxianus cells immobilized in calcium alginate gel beads. A maximum ethanol concentration of 111 g/l was achieved at an initial sugar concentration of 260 g/l in 20 hours, when the immobilized cell concentration in the calcium alginate beads was 53.3 g dry wt./l bead volume. Ethanol yield remained almost unaffected by initial sugar concentration up to 250 g/l and was found to be about 88% of the theoretical. Maximum rate of ethanol production decreased from 22.5 g ethanol/l/h to 10.5 g ethanol/l/h while the maximum rate of total sugars utilization decreased from 74.9 g sugars/l/h to 28.5 g sugars/l/h as the initial substrate concentration was increased from 100 to 300 g/l. The concentration of free cells in the fermentation broth was low.     

Optimization of butanol production from tropical maize stalk juice by fermentation with Clostridium beijerinckii NCIMB 8052

Mixed sugars from tropical maize stalk juice were used to carry out butanol fermentation with Clostridium beijerinckii NCIMB 8052. Batch experiments employing central composite design (CCD) and response surface methodology (RSM) optimization were performed to evaluate effects of three factors, i.e. pH, initial total sugar concentration, and agitation rate on butanol production. Optimum conditions of pH 6.7, sugar concentration 42.2 g/L and agitation rate 48 rpm were predicted, under which a maximum butanol yield of 0.27 g/g-sugar was estimated. Further experiments demonstrated that higher agitation facilitated acetone production, leading to lower butanol selectivity in total acetone–butanol–ethanol (ABE). While glucose and fructose are more preferable by C. beijerinckii, sucrose can also be easily degraded by the microorganism. This study indicated that RSM is a useful approach for optimizing operational conditions for butanol production, and demonstrated that tropical maize, with high yield of biomass and stalk sugars, is a promising biofuel crop.     

Co-fermentation of a mixture of glucose and xylose to ethanol by Zymomonas mobilis and Pachysolen tannophilus

This research was designed to maximize ethanol production from a glucose-xylose sugar mixture (simulating a sugar cane bagasse hydrolysate) by co-fermentation with Zymomonas mobilis and Pachysolen tannophilus. The volumetric ethanol productivity of Z. mobilis with 50 g glucose/l was 2.87 g/l/h, giving an ethanol yield of 0.50 g/g glucose, which is 98% of the theoretical. P. tannophilus when cultured on 50 g xylose/l gave a volumetric ethanol productivity of 0.10 g/l/h with an ethanol yield of 0.15 g/g xylose, which is 29% of the theoretical. On optimization of the co-fermentation with the sugar mixture (60 g glucose/l and 40 g xylose/l) a total ethanol yield of 0.33 g/g sugar mixture, which is 65% of the theoretical yield, was obtained. The co-fermentation increased the ethanol yield from xylose to 0.17 g/g. Glucose and xylose were completely utilized and no residual sugar was detected in the medium at the end of the fermentation. The pH of the medium was found to be a good indicator of the fermentation status. The optimum conditions were a temperature of 30°C, initial inoculation with Z. mobilis and incubation with no aeration, inactivation of bacterium after the utilization of glucose, followed by inoculation with P. tannophilus and incubation with limited aeration.     

Optimization of process parameters for ethanol production from sugar cane molasses by Zymomonas mobilis using response surface methodology and genetic algorithm

Ethanol is a potential energy source and its production from renewable biomass has gained lot of popularity. There has been worldwide research to produce ethanol from regional inexpensive substrates. The present study deals with the optimization of process parameters (viz. temperature, pH, initial total reducing sugar (TRS) concentration in sugar cane molasses and fermentation time) for ethanol production from sugar cane molasses by Zymomonas mobilis using Box–Behnken experimental design and genetic algorithm (GA). An empirical model was developed through response surface methodology to analyze the effects of the process parameters on ethanol production. The data obtained after performing the experiments based on statistical design was utilized for regression analysis and analysis of variance studies. The regression equation obtained after regression analysis was used as a fitness function for the genetic algorithm. The GA optimization technique predicted a maximum ethanol yield of 59.59 g/L at temperature 31 °C, pH 5.13, initial TRS concentration 216 g/L and fermentation time 44 h. The maximum experimental ethanol yield obtained after applying GA was 58.4 g/L, which was in close agreement with the predicted value.     

Ethanol production from xylose by Fusarium oxysporum and the optimization of culture conditions

Bioethanol is the most commonly used renewable biofuel as an alternative to fossil fuels. Many microbial strains can convert lignocellulosics into bioethanol. However, very few natural strains with a high capability of fermenting pentose sugars and simultaneously utilizing various sugars have been reported. In this study, fermentation of sugar by Fusarium oxysporum G was performed for the production of ethanol to improve the performance of the fermentation process. The influences of pH, substrate concentration, temperature, and rotation speed on ethanol fermentation are investigated. The three significant factors (pH, substrate concentration, and temperature) are further optimized by quadratic orthogonal rotation regression combination design and response surface methodology (RSM). The optimum conditions are pH 4, 40?g/L of xylose, 32?°C, and 110?rpm obtained through single factor experiment design. Finally, it is found that the maximum ethanol production (10.0?g/L) can be achieved after 7 d of fermentation under conditions of pH 3.87, 45.2?g/L of xylose, and 30.4?°C. Glucose is utilized preferentially for the glucose–xylose mixture during the initial fermentation stage, but glucose and xylose are synchronously consumed without preference in the second period. These findings are significant for the potential industrial application of this strain for bioethanol production.     

Ethanol production from concentrated food waste hydrolysates with yeast cells immobilized on corn stalk

The aim of the present study was to examine ethanol production from concentrated food waste hydrolysates using whole cells of S. cerevisiae immobilized on corn stalks. In order to improve cell immobilization efficiency, biological modification of the carrier was carried out by cellulase hydrolysis. The results show that proper modification of the carrier with cellulase hydrolysis was suitable for cell immobilization. The mechanism proposed, cellulase hydrolysis, not only increased the immobilized cell concentration, but also disrupted the sleek surface to become rough and porous, which enhanced ethanol production. In batch fermentation with an initial reducing sugar concentration of 202.64 ± 1.86 g/l, an optimal ethanol concentration of 87.91 ± 1.98 g/l was obtained using a modified corn stalk-immobilized cell system. The ethanol concentration produced by the immobilized cells was 6.9% higher than that produced by the free cells. Ethanol production in the 14th cycle repeated batch fermentation demonstrated the enhanced stability of the immobilized yeast cells. Under continuous fermentation in an immobilized cell reactor, the maximum ethanol concentration of 84.85 g/l, and the highest ethanol yield of 0.43 g/g (of reducing sugar) were achieved at hydraulic retention time (HRT) of 3.10 h, whereas the maximum volumetric ethanol productivity of 43.54 g/l/h was observed at a HRT of 1.55 h.     

Optimization of Process Conditions Using Response Surface Methodology (RSM) for Ethanol Production from Pretreated Sugarcane Bagasse: Kinetics and Modeling

Based on a five level central composite design (CCD) involving the variables substrate concentration (C), pH (P), incubation temperature (T) and fermentation time (H), a response surface methodology (RSM) for the production of ethanol from pretreated sugarcane bagasse by cellulase and yeast Kluyveromyces fragilis was standardized. The design contains a total of 31 experimental trials in which the first 24 organized in a factorial design and from 25 to 31 involving the replications of the central points. Data obtained from RSM on ethanol production were subjected to the analysis of variance (ANOVA) and analyzed using a second order polynomial equation. Maximum ethanol concentration (32.6 g/l) was obtained from 180 g/l pretreated sugarcane bagasse at the optimized process conditions (temperature 35°C, pH 5.5) in 72 h aerobic batch fermentation. Various kinetic models such as logistic model, logistic incorporated leudeking piret model and logistic incorporated modified leudeking piret model have been evaluated and the constants were predicted.     

Production of Fructose and Ethanol from Cane Molasses Using Saccharomyces cerevisiae ATCC 36858

The purpose of this research was to study the possibility of the production of ethanol and enriched fructose syrups from sugar cane molasses using the yeast Saccharomyces cerevisiae ATCC 36858. In batch experiments with a total sugar concentration of between 96.7 g/l and 323.5 g/l, the fructose yield was above 90% of the theoretical value. The ethanol yield and volumetric productivity were in the range of 66% and 77% of the theoretical value, and between 0.53 g ethanol/l × h and 3.15 g ethanol/l × h, respectively. The fructose fraction in the carbohydrates content of the produced syrups was more than 95% when the total initial sugar concentration in the medium was below 273.8 g/l. Some oligosaccharides and glycerol were also produced in all tested media. The maximum amount of produced oligosaccharides including raffinose accounted for 13.4 g/l in the cane molasses medium with 323.5 g/l sugars in the initial phase of the fermentation process. The oligosaccharides produced and raffinose were completely consumed by the end of the fermentation process when the total initial sugar concentration was less than 191.3 g/l. The glycerol concentration was below 9.9 g/l. These findings are useful in the production of ethanol and high fructose syrups using sugar cane molasses.     

Optimization of fermentation conditions for the production of ethanol from sago starch by co-immobilized amyloglucosidase and cells of Zymomonas mobilis using response surface methodology

Statistical experimental design was used to optimize the conditions of simultaneous saccharification and fermentation (SSF), viz. temperature, pH and time of fermentation of ethanol from sago starch with co-immobilized amyloglucosidase (AMG) and Zymomonas mobilis MTCC 92 by submerged fermentation. Maximum ethanol concentration of 55.3 g/l was obtained using a starch concentration of 150 g/l. The optimum conditions were found to be a temperature of 32.4 °C, pH of 4.93 and time of fermentation of 17.24 h. Thus, by using SSF process with co-immobilized AMG and Z. mobilis cells MTCC 92, the central composite design (CCD) was found to be the most favourable strategy investigated with respect to ethanol production and enzyme recovery.     

Direct fermentation of potato starch wastewater to lactic acid by Rhizopus oryzae and Rhizopus arrhizus

The biochemical kinetic of direct fermentation for lactic acid production by fungal species of Rhizopus arrhizus 3,6017 and Rhizopus oryzae 2,062 was studied with respect to growth pH, temperature and substrate. The direct fermentation was characterized by starch hydrolysis, accumulation of reducing sugar, and production of lactic acid and fungal biomass. Starch hydrolysis, reducing sugar accumulation, biomass formation and lactic acid production were affected with the variations in pH, temperature, and starch source and concentration. A growth condition with starch concentration approximately 20 g/l at pH 6.0 and 30°C was favourable for both starch saccharification and lactic acid fermentation, resulting in lactic acid yield of 0.87–0.97 g/g starch associated with 1.5–2.0 g/l fungal biomass produced in 36 h fermentation. R. arrhizus 3,6017 had a higher capacity to produce lactic acid, while R. oryzae 2,062 produced more fungal biomass under similar conditions.     

Fermentation of sugar cane bagasse hemicellulosic hydrolysate and sugar mixtures to ethanol by recombinant Escherichia coli KO11

Escherichia coli KO11, carrying the ethanol pathway genes pdc (pyruvate decarboxylase) and adh (alcohol dehydrogenase) from Zymomonas mobilis integrated into its chromosome, has the ability to metabolize pentoses and hexoses to ethanol, both in synthetic medium and in hemicellulosic hydrolysates. In the fermentation of sugar mixtures simulating hemicellulose hydrolysate sugar composition (10.0 g of glucose/l and 40.0 g of xylose/l) and supplemented with tryptone and yeast extract, recombinant bacteria produced 24.58 g of ethanol/l, equivalent to 96.4% of the maximum theoretical yield. Corn steep powder (CSP), a byproduct of the corn starch-processing industry, was used to replace tryptone and yeast extract. At a concentration of 12.5 g/l, it was able to support the fermentation of glucose (80.0 g/l) to ethanol, with both ethanol yield and volumetric productivity comparable to those obtained with fermentation media containing tryptone and yeast extract. Hemicellulose hydrolysate of sugar cane bagasse supplemented with tryptone and yeast extract was also readily fermented to ethanol within 48 h, and ethanol yield achieved 91.5% of the theoretical maximum conversion efficiency. However, fermentation of bagasse hydrolysate supplemented with 12.5 g of CSP/l took twice as long to complete. This revised version was published online in November 2006 with corrections to the Cover Date.     

Ethanol fermentation in an immobilized cell reactor using Saccharomyces cerevisiae

Fermentation of sugar by Saccharomyces cerevisiae, for production of ethanol in an immobilized cell reactor (ICR) was successfully carried out to improve the performance of the fermentation process. The fermentation set-up was comprised of a column packed with beads of immobilized cells. The immobilization of S. cerevisiae was simply performed by the enriched cells cultured media harvested at exponential growth phase. The fixed cell loaded ICR was carried out at initial stage of operation and the cell was entrapped by calcium alginate. The production of ethanol was steady after 24 h of operation. The concentration of ethanol was affected by the media flow rates and residence time distribution from 2 to 7 h. In addition, batch fermentation was carried out with 50 g/l glucose concentration. Subsequently, the ethanol productions and the reactor productivities of batch fermentation and immobilized cells were compared. In batch fermentation, sugar consumption and ethanol production obtained were 99.6% and 12.5% v/v after 27 h while in the ICR, 88.2% and 16.7% v/v were obtained with 6 h retention time. Nearly 5% ethanol production was achieved with high glucose concentration (150 g/l) at 6 h retention time. A yield of 38% was obtained with 150 g/l glucose. The yield was improved approximately 27% on ICR and a 24 h fermentation time was reduced to 7 h. The cell growth rate was based on the Monod rate equation. The kinetic constants (K(s) and mu(m)) of batch fermentation were 2.3 g/l and 0.35 g/lh, respectively. The maximum yield of biomass on substrate (Y(X-S)) and the maximum yield of product on substrate (Y(P-S)) in batch fermentations were 50.8% and 31.2% respectively. Productivity of the ICR were 1.3, 2.3, and 2.8 g/lh for 25, 35, 50 g/l of glucose concentration, respectively. The productivity of ethanol in batch fermentation with 50 g/l glucose was calculated as 0.29 g/lh. Maximum production of ethanol in ICR when compared to batch reactor has shown to increase approximately 10-fold. The performance of the two reactors was compared and a respective rate model was proposed. The present research has shown that high sugar concentration (150 g/l) in the ICR column was successfully converted to ethanol. The achieved results in ICR with high substrate concentration are promising for scale up operation. The proposed model can be used to design a lager scale ICR column for production of high ethanol concentration.     

Bioconversion of palm oil mill effluent for citric acid production: statistical optimization of fermentation media and time by central composite design

A laboratory-scale study was conducted to evaluate the feasibility of using palm oil mill effluent (POME) as a major substrate and other nutrients for maximum production of citric acid using the potential fungal strain Aspergillus niger (A103). Statistical optimization of medium composition (substrate–POME, co-substrates–wheat flour and glucose, and nitrogen source–ammonium nitrate) and fermentation time was carried out by central composite design (CCD) to develop a polynomial regression model through the effects of linear, quadratic, and interaction of the factors. The statistical analysis of the results showed that, in the range studied, ammonium nitrate had no significant effect whereas substrate, co-substrates and fermentation time had significant effects on citric acid production. The optimized medium containing 2% (w/w) of substrate concentration (POME), 4% (w/w) of wheat flour concentration, 4% (w/w) of glucose concentration, 0% (w/v) of ammonium nitrate and 5 days fermentation time gave the maximum predicted citric acid of 5.37 g/l which was found to be 1.5 g/l in the experimental run. The determination of coefficient (R ²) from the analysis observed was 0.964, indicating a satisfactory adjustment of the model with the response. The analysis showed that the major substrate POME (P < 0.05), glucose (P < 0.01), nutrient (P < 0.05), and fermentation time (P < 0.01) was more significant for citric acid production. The bioconversion of POME for citric acid production using optimal conditions showed the higher removal of chemical oxygen demand (82%) with the production of citric acid (5.2 g/l) on the final day of fermentation process (7 days). The pH and biosolids accumulation were observed during the bioconversion process.     

The effect of pH,temperature and sucrose concentration on high productivity continuous ethanol fermentation using Zymomonas mobilis

Summary A flocculent strain of Zymomonas mobilis was used for ethanol production from sucrose. Using a fermentor with cell recycle (internal and external settler) high sugar conversion and ethanol productivity were obtained. At a dilution rate of 0.5 h^-1 (giving 96% sugar conversion) the ethanol productivity, yield and concentrations respectively were 20 g/l/h, 0.45 g/g and 40 g/l using a medium containing 100 g/l sucrose. At a sucrose concentration of 150 g/l, the ethanol concentration reached 60 g/l. The ethanol yield was 80% theoretical due to levan and fructo-oligomer formation. No sorbitol was detected. This fermentation was conducted at a range of conditions from 30 to 36°C and from pH 4.0 to 5.5.     

Production of fuel ethanol from bamboo by concentrated sulfuric acid hydrolysis followed by continuous ethanol fermentation

An efficient process for the production of fuel ethanol from bamboo that consisted of hydrolysis with concentrated sulfuric acid, removal of color compounds, separation of acid and sugar, hydrolysis of oligosaccharides and subsequent continuous ethanol fermentation was developed. The highest sugar recovery efficiency was 81.6% when concentrated sulfuric acid hydrolysis was carried out under the optimum conditions. Continuous separation of acid from the saccharified liquid after removal of color compounds with activated carbon was conducted using an improved simulated moving bed (ISMB) system, and 98.4% of sugar and 90.5% of acid were recovered. After oligosaccharide hydrolysis and pH adjustment, the unsterilized saccharified liquid was subjected to continuous ethanol fermentation using Saccharomycescerevisiae strain KF-7. The ethanol concentration, the fermentation yield based on glucose and the ethanol productivity were approximately 27.2 g/l, 92.0% and 8.2 g/l/h, respectively. These results suggest that the process is effective for production of fuel ethanol from bamboo.     

The effect of temperature,pH, and initial glucose concentration on the kinetics of ethanol production by Zymomonas mobilis in batch fermentation

Summary Zymomonas mobilis, strain ATCC 10988, was used to evaluate the effects of pH (5.0 to 8.0), temperature (30°C to 40°C), and initial glucose concentration (75 g/l to 150 g/l) on the kinetics of ethanol production from glucose using batch fermentation. Specific ethanol production rate was maximum and nearly constant over a pH range of 6.0 to 7.5. End-of-batch ethanol yield and specific growth rate were insensitive to pH in the range of 5.0 to 7.5. End-of-batch ethanol yield was maximum and nearly constant between 30°C and 37°C but decreased by 24% between 37°C and 40°C. All other kinetic parameters are greatest at 34°C. End-of-batch ethanol yield is maximum at an initial glucose concentration of 100 g/l. Specific growth rate reaches a maximum at 75 g/l, but specific ethanol production rate decreases throughout the range. The optimum initial glucose concentration of 100 g/l gives the highest ethanol yield at a specific ethanol production rate less than 10% below the maximum observed.     

Simultaneous saccharification and ethanol fermentation of oxalic acid pretreated corncob assessed with response surface methodology

Response surface methodology was used to evaluate optimal time, temperature and oxalic acid concentration for simultaneous saccharification and fermentation (SSF) of corncob particles by Pichia stipitis CBS 6054. Fifteen different conditions for pretreatment were examined in a 2³ full factorial design with six axial points. Temperatures ranged from 132 to 180 °C, time from 10 to 90 min and oxalic acid loadings from 0.01 to 0.038 g/g solids. Separate maxima were found for enzymatic saccharification and hemicellulose fermentation, respectively, with the condition for maximum saccharification being significantly more severe. Ethanol production was affected by reaction temperature more than by oxalic acid and reaction time over the ranges examined. The effect of reaction temperature was significant at a 95% confidence level in its effect on ethanol production. Oxalic acid and reaction time were statistically significant at the 90% level. The highest ethanol concentration (20 g/l) was obtained after 48 h with an ethanol volumetric production rate of 0.42 g ethanol l⁻¹ h⁻¹. The ethanol yield after SSF with P. stipitis was significantly higher than predicted by sequential saccharification and fermentation of substrate pretreated under the same condition. This was attributed to the secretion of β-glucosidase by P. stipitis. During SSF, free extracellular β-glucosidase activity was 1.30 pNPG U/g with P. stipitis, while saccharification without the yeast was 0.66 pNPG U/g.     

海带发酵制取生物乙醇的影响因素与优化条件

针对海带的碳水化合物不易被单一菌株发酵转化为乙醇的难题,通过酸化、匀浆和消化等预处理和正交试验,利用多酶系多菌种微生物复合发酵剂的酿酒曲,研究海带发酵制取生物乙醇的影响因素与优化条件。结果表明:在预处理试验中,加入一定量的Na2CO3,可以提高海带液中还原性糖和总糖的含量;消化温度对总糖影响相对较大,而对还原性糖的影响较小;过滤不利于得到较高浓度的乙醇;在优化条件中,发酵液的初始酸碱度是最重要的,其次是发酵温度和基质浓度,发酵液体积的影响程度相对较小。在基质(海带)质量浓度为0.15 g/L、温度34℃、起始pH 6.5和发酵液体积200 mL时,可以获得最大的乙醇产量4.09 g(以100 g海带计)。