Initial Total Sugar Concentration Research Articles

Enhancing and monitoring spore production in Clostridium butyricum using pH-based regulation strategy and a robust soft sensor based on back-propagation neural networks.

Clostridium butyricumis a probiotic that forms anaerobic spores and plays a crucial role in regulating gut microbiota. However, the total viable cell count and spore yield of C. butyricum in industrial production are comparatively low. To this end, we investigated the metabolic characteristics of the strain and proposed three distinct pH regulation strategies for enhancing spore production. In addition, precise measurement of fermentation parameters such as substrate concentration, total viable cell count, and spore concentration is crucial for successful industrial probiotics production. Nevertheless, online measurement of these intricate parameters in the fermentation of C. butyricum poses a considerable challenge owing to the complex, nonlinear, multivariate, and strongly coupled characteristics of the production process. Therefore, we analyzed the capacitance and conductivity acquired from a viable cell sensor as the core parameters for the fermentation process. Subsequently, a robust soft sensor was developed using a seven-input back-propagation neural network model with input variables of fermentation time, capacitance, conductivity, pH, initial total sugar concentration, ammonium ion concentration, and calcium ion concentration. The model enables the online monitoring of total viable biomass count, substrate concentrations, and spore yield, and can be extended to similar fermentation processes with pH changes as a characteristic feature.

Mathematical modeling of bioethanol production from sweet sorghum juice under high gravity fermentation: Applicability of Monod-based, logistic, modified Gompertz and Weibull models

BackgroundMathematical modeling of a fermentation process is crucial in understanding and predicting dynamics of the process, which can be used in process improvement, design and control. The present study aimed to develop Monod-based kinetic models to describe cell growth, substrate consumption and ethanol production by Saccharomyces cerevisiae NP 01 under high gravity (HG) fermentation of sweet sorghum juice (SSJ). ResultsThe fermentation using an initial total sugar (TS) concentration of 240 g/L resulted in 113.3 g/L of ethanol production, with 90.9% TS consumption and a fermentation efficiency of 94.4%. Growth of the yeast in terms of specific growth rate was found to be inhibited at a threshold TS concentration of 65 g/L, and the maximum specific growth rate, Monod constant and inhibition constant were 0.45 1/h, 19.5 g/L and 0.002 L/(g·h), respectively. Monod-based models incorporating substrate and product inhibition terms showed high applicability to describe the changes of cell, TS and ethanol concentrations, based on the values of bias factor, accuracy factor, coefficient of determination and root mean square error. ConclusionsThe Monod-based models fitted the data equally well as compared with the logistic, modified Gompertz, and Weibull models, despite estimating the value of different kinetic parameters. These results demonstrated that all the models tested were applicable in modeling HG ethanol fermentation.How to cite: Salakkam A, Phukoetphim N, Laopaiboon P, et al. Mathematical modeling of bioethanol production from sweet sorghum juice under high gravity fermentation: Applicability of Monod-based, logistic, modified Gompertz and Weibull models. Electron J Biotechnol 2023;64. https://doi.org/10.1016/j.ejbt.2023.03.004.

Microalga Coelastrella sp. Cultivation on Unhydrolyzed Molasses-Based Medium towards the Optimization of Conditions for Growth and Biomass Production under Mixotrophic Cultivation.

Improving biomass production with the utilization of low-cost substrate is a crucial approach to overcome the hindrance of high cost in developing large-scale microalgae production. The microalga Coelastrella sp. KKU-P1 was mixotrophically cultivated using unhydrolyzed molasses as a carbon source, with the key environmental conditions being varied in order to maximize biomass production. The batch cultivation in flasks achieved the highest biomass production of 3.81 g/L, under an initial pH 5.0, a substrate to inoculum ratio of 100:3, an initial total sugar concentration of 10 g/L, and a sodium nitrate concentration of 1.5 g/L with continuous light illumination at 23.7 W/m2. The photobioreactor cultivation results indicated that CO2 supplementation did not improve biomass production. An ambient concentration of CO2 was sufficient to promote the mixotrophic growth of the microalga as indicated by the highest biomass production of 4.28 g/L with 33.91% protein, 46.71% carbohydrate, and 15.10% lipid. The results of the biochemical composition analysis suggest that the microalgal biomass obtained is promising as a source of essential amino acids and pigments as well as saturated and monounsaturated fatty acids. This research highlights the potential for bioresource production via microalgal mixotrophic cultivation using untreated molasses as a low-cost raw material.

Using a Novel Pervaporative Sequential-Co-immobilized Two-Sectional Bioreactor with an Ultralow Fouling–Biofouling Superhydrophobic Silicallite-1/PDMS Membrane to Enhance Bioethanol Production

This study is on the efficient fermentation of high glucose (G) and xylose (X) levels (G/X ratio of 1.5:1), simulating the hydrolysate of lignocellulosic wastes, via an innovative integrated two-stage fermentation–pervaporation process. Immobilized Zymomonas mobilis (Z) and Pichia stipitis (P) were exploited in a sequential-co-immobilized culture (Z in the first stage and Z and P in second stage) to simultaneously increase bioethanol productivity and lessen the inhibitions. The threshold inhibition was evaluated in 100 mL shake flasks by raising the initial total sugar concentration from 50 to 200 g/L where complete inhibition was observed at 200 g/L. Subsequently, fermentation (G: 120 g/L, X: 80 g/L) was examined in a sequential-co-immobilized two-sectional bioreactor (ITB-2L) during 200 h. ITB resulted in 100% glucose and 16% xylose conversion, showing ethanol productivity of 0.26 g/L·h and yield of 0.4 ge/gs. To investigate the effect of reducing inhibitions, a tubular superhydrophobic silicalite-1/PDMS pervaporative (TSP) autoclavable membrane with antiswelling properties was fabricated. The pervaporative sequential-co-immobilized two-sectional bioreactor (PITB) using TSP enhanced xylose conversion (57%), ethanol productivity (0.39 g/L·h), and yield (0.47 ge/gs). The membrane surface was probed after 161 h of usage, and the limited presence of only negative ions on its surface proved its superior ultralow fouling–biofouling formation. PITB proved itself as a robust integrated process for the second-generation bioethanol production.

Enhanced Cadaverine Production by Engineered Escherichia coli Using Soybean Residue Hydrolysate (SRH) as a Sole Nitrogen Source.

An economical source of nitrogen is one of the major limiting factors for sustainable cadaverine production. The utilization potential of soybean residue for enhanced cadaverine production by engineered Escherichia coli DFC1001 was investigated in this study. The SRH from soybean residue could get the protein extraction rate (PE) of 67.51% and the degree of protein hydrolysis (DH) of 22.49%. The protein molecular weights in SRH were mainly distributed in 565Da (72.28%) and 1252Da (17.11%). These proteins with small molecular weights and concentrated molecular weight distribution were favorable to be transformed by engineered E. coli DFC1001, and then SRH replaced completely yeast powder as an only nitrogen source for cadaverine production. The maximum cadaverine productivity was 0.52g/L/h, achieved with a constant speed feeding strategy in the optimized SRH fermentation medium containing an initial total sugar concentration of 30g/L and exogenous added minerals, which indicated that soybean residue could be a potential feedstock for economic cadaverine production.

Sequential dark and photo-fermentative hydrogen gas production from agar embedded molasses

In this study, molasses and dark fermentation effluent were solidified using agar and used for H2 production by dark and photo-fermentation. During dark fermentation, the solid jelly form of molasses enabled a slow release of the substrate to the liquid broth hindering fast pH decreases. The initial total sugar concentration, H2 yield, H2 rate and lag phase in dark fermentation were 36.2 g/L, 226.24 mL H2/g TS, 29.85 mL H2/h and 4.37 h, respectively. Photo-fermentation of 5.77 g TVFA/L embedded dark fermentation effluent did not lead to efficient H2 production. The best performance in photo-fermentation was obtained with 1.55 g TVFA/L containing diluted dark fermentation effluent. The H2 yield, H2 rate and lag phase in photo-fermentation were 870.26 mL H2/g TVFA, 0.913 mL H2/h and 54.07 h, respectively. Embedding concentrated substrate using agar can enhance H2 production performance but only if the release of the substrate does not exceed inhibitory levels and if the rate of diffusion is tolerable for microbial activity.

Effect of Myclobutanil Pesticide on the Physiological Behavior of Two Newly Isolated Saccharomyces cerevisiae Strains during Very-High-Gravity Alcoholic Fermentation.

Yeasts are able to act as biosorbents, as their cell wall includes several components capable of binding organic xenobiotic compounds that can potentially be removed during various fermentation processes. In the present investigation, two novel Saccharomyces cerevisiae strains (LMBF-Y 16 and LMBF-Y-18), previously isolated from grapes, were studied regarding their physiological behavior (dry cell weight—DCW production, substrate uptake, and ethanol and glycerol biosynthesis) during fermentations of grape must, in some cases enriched with commercial glucose and fructose (initial total sugar concentration approximately 150 and 250 g/L, respectively). Myclobutanil (a chiral triazole fungicide broadly used as a protective agent of vine) was also added to the culture media at various concentrations in order to assess the ability of the yeasts to simultaneously perform alcoholic fermentations and detoxify the medium (i.e., to remove the fungicide). In the first set of experiments and for both tested strains, trials were carried out in either 250 mL or 2.0 L agitated shake flasks in either synthetic glucose-based experiments or grape musts. Since the results obtained in the trials where the cultures were placed in 2.0 L flasks with grape musts as substrates were superior in terms of both DCW and ethanol production, these experimental conditions were selected for the subsequent studies. Both strains showed high fermentative efficiency, producing high amounts of DCW (9.5–10.5 g/L) in parallel with high ethanol production, which in some cases achieved values very close to the maximum theoretical ethanol production yield (≈0.49 g of ethanol per g of sugar). When using grape must with initial total sugars at approximately 250 g/L (very high gravity fermentation media, close to winemaking conditions), significantly high ethanol quantities (i.e., ranging between 105 and 123 g/L) were produced. Myclobutanil addition slightly negatively affected sugar conversion into ethanol; however, in all cases, ethanol production was very satisfactory. A non-negligible myclobutanil removal during fermentation, which ranged between 5%–27%, as a result of the adsorptive or degradative capacity of the yeast was also reported. The presence of myclobutanil had no effect on DCW production and resulted in no significant differences in the biosynthesis of glycerol. Therefore, these newly isolated yeast strains could be excellent candidates for simultaneous high ethanol production and parallel pesticide removal in a general biorefinery concept demonstrating many environmental benefits.

Improvement in the yield and selectivity of lactulose synthesis with Bacillus circulans β-galactosidase

A commercial preparation of β-galactosidase from Bacillus circulans was evaluated as catalyst in the synthesis of lactulose considering temperature, pH, initial total sugar concentration, enzyme to initial lactose mass ratio and fructose to lactose molar ratio (F/L) as variables. The results obtained in terms of selectivity (SLu) yield (YLu) and productivity (πLu) of lactulose synthesis showed that only the initial total sugar concentration and lactose to fructose molar ratio were significant, the latter strongly affecting SLu. Best results were obtained at F/L of 20, being YLu = 0.54, πLu = 0.043 g h−1·mg enz−1, and SLu = 30.9. Under these conditions lactulose synthesis was favored over transgalactosylated oligosaccharides (TOS), due to the higher chance of transferring the galactosyl group into fructose at high F/L. Yields of lactulose and TOS depended on the enzyme origin, while their maximum concentrations were obtained at different lactose conversions (at 0.7 for lactulose and at 0.45 for TOS) and depended on the kinetics of reactions. Yields attained with Bacillus circulans β-galactosidase are higher than obtained with enzymes from other origin at comparable conditions, so this system is a preferred option for lactulose production.

Sequential fermentation of hydrogen and methane from steam-exploded sugarcane bagasse hydrolysate

The goal of this study was to sequential fermentation of hydrogen and methane from sugarcane bagasse (SCB). Steam explosion conditions for pretreating SCB were optimum at 195 °C and 1.5 min, which yielded 36.35 g/L of total sugar and 2.35 g/L of total inhibitors. Under these conditions (all in g/L): glucose, 11.33; xylose, 24.41; arabinose, 0.61; acetic acid, 2.33; and furfural, 0.02 were obtained. The resulting hydrolysate was used to produce hydrogen by anaerobic mixed cultures. A maximum hydrogen production rate of 396.50 mL H2/L day was achieved at an initial pH of 6 and an initial total sugar concentration of 10 g/L. The effluent from the hydrogen fermentation process was further used to produce methane. Response surface methodology with central composite design was used to obtain the suitable conditions for maximizing methane production rate (MPR). An MPR of 185.73 mL/L day was achieved at initial pH, Ni and Fe concentrations of 7.59, 3.61 mg/L and 8.44 mg/L, respectively. Total energy of 304.11 kJ/L-substrate was obtained from a sequential fermentation of hydrogen and methane. This approach will not only add value to SCB, in the form of safe and clean energy, but also provide a solution for making use of this abundant waste.

Optimization of particle number, substrate concentration and temperature of batch immobilized reactor system for biohydrogen production by dark fermentation

Immobilized cell bioreactor was operated in batch mode for biohydrogen generation by dark fermentation from acid hydrolyzed waste wheat powder. It was aimed to optimize the fermentation conditions with the purpose of obtaining the highest hydrogen yield (YH2) and production rate (HPR) by applying Box–Wilson statistical experimental design method. Particle number (PN = 120–240; X1), initial total sugar concentration (TS0 = 10–30 g/l; X2) and fermentation temperature (T = 35–55 °C; X3) were selected as independent variables. Polyester fibers with particle diameter “Dp” = 0.5 cm were used as support material to immobilize microorganisms with heat-pretreated sludge. Quadratic equations for production yield and rate were developed by using experimental results. The maximum YH2 (3.21 mol H2/mol glucose) and HPR (73.3 ml H2/h) were predicted at the optimum conditions of PN = 240, TS0 = 10 g/l and T = 44.9 °C. Also, analysis of variance, as well as sum of ranking difference test results demonstrated that fitting models were statistically significant.

Pretreatment conditions of palm oil mill effluent (POME) for thermophilic biohydrogen production by mixed culture

The availability of fermentable sugars in POME is one of the critical factors that determine the fermentative biohydrogen production yield. This study was carried out to determine the pretreatment conditions viz., temperature, hydrolysis time and acid concentration that can yield the highest monomeric sugars, to be utilized for production of biohydrogen from POME by mixed culture dark fermentation. Two different acids were used, nitric acid and phosphoric acid in the pretreatment of POME. Batch fermentation was performed to determine the potential of pretreated POME as a substrate for the production of biohydrogen under the tested pretreatment conditions. Higher hydrogen yield was successfully achieved using pretreated POME as compared to raw POME by mixed culture. Maximum hydrogen production was 0.181 (mmol/L/h), which corresponded to the yield of 1.24 mol H2/mol glucose achieved at 0.8% (w/v) phosphoric acid with initial total reducing sugar concentration of 18.47 g/L. Hence, the results implied that POME pretreated with 0.8% (w/v) phosphoric acid is a potential substrate for efficient biohydrogen fermentation yield that is 97% higher than untreated POME. While POME pretreated with 1% (w/v) of nitric acid showed 65% improvement in biohydrogen yield as compared to untreated POME. Therefore, the results implied that both pretreatment methods of POME showed significant increase in the biohydrogen production.

Fermentative hydrogen production from Jerusalem artichoke by Clostridium tyrobutyricum expressing exo-inulinase gene

Clostridium tyrobutyricum ATCC25755 has been reported as being able to produce significant quantities of hydrogen. In this study, the exo-inulinase encoding gene cloned from Paenibacillus polymyxa SC-2 was into the expression plasmid pSY6 and expressed in the cells of C. tyrobutyricum. The engineered C. tyrobutyricum strain efficiently fermented the inulin-type carbohydrates from Jerusalem artichoke, without any pretreatment being necessary for the production of hydrogen. A comparatively high hydrogen yield (3.7 mol/mol inulin-type sugar) was achieved after 96 h in a batch process with simultaneous saccharification and fermentation (SSF), with an overall volumetric productivity rate of 620 ± 60 mL/h/L when the initial total sugar concentration of the inulin extract was increased to 100 g/L. Synthesis of inulinase in the batch SSF culture was closely associated with strain growth until the end of the exponential phase, reaching a maximum activity of 28.4 ± 0.26 U/mL. The overall results show that the highly productive and abundant biomass crop Jerusalem artichoke can be a good substrate for hydrogen production, and that the application of batch SSF for its conversion has the potential to become a cost-effective process in the near future.

Metabolic engineering of Clostridium tyrobutyricum for enhanced butyric acid production from glucose and xylose

Clostridium tyrobutyricum is a promising microorganism for butyric acid production. However, its ability to utilize xylose, the second most abundant sugar found in lignocellulosic biomass, is severely impaired by glucose-mediated carbon catabolite repression (CCR). In this study, CCR in C. tyrobutyricum was eliminated by overexpressing three heterologous xylose catabolism genes (xylT, xylA and xlyB) cloned from C. acetobutylicum. Compared to the parental strain, the engineered strain Ct-pTBA produced more butyric acid (37.8g/L vs. 19.4g/L) from glucose and xylose simultaneously, at a higher xylose utilization rate (1.28g/L·h vs. 0.16g/L·h) and efficiency (94.3% vs. 13.8%), resulting in a higher butyrate productivity (0.53g/L·h vs. 0.26g/L·h) and yield (0.32g/g vs. 0.28g/g). When the initial total sugar concentration was ~120g/L, both glucose and xylose utilization rates increased with increasing their respective concentration or ratio in the co-substrates but the total sugar utilization rate remained almost unchanged in the fermentation at pH 6.0. Decreasing the pH to 5.0 significantly decreased sugar utilization rates and butyrate productivity, but the effect was more pronounced for xylose than glucose. The addition of benzyl viologen (BV) as an artificial electron carrier facilitated the re-assimilation of acetate and increased butyrate production to a final titer of 46.4g/L, yield of 0.43g/g sugar consumed, productivity of 0.87g/L·h, and acid purity of 98.3% in free-cell batch fermentation, which were the highest ever reported for butyric acid fermentation. The engineered strain with BV addition thus can provide an economical process for butyric acid production from lignocellulosic biomass.

The effect of support particle type on thermophilic hydrogen production by immobilized batch dark fermentation

The objective of the study was to select microorganism support particle to enhance hydrogen production in an immobilized system by dark fermentation. Stainless steel scrubber, volcanic stone, tulle, polyester fiber, loofah sponge, plastic bath sponge, sea sponge and aquarium biological sponges were used as support materials to investigate hydrogen production potentials of these particles. Waste wheat was the substrate and it was hydrolyzed in diluted sulfuric acid at high temperature to obtain sugar solution. Heat and acid pretreatment method was applied to anaerobic sludge to eliminate methanogens and to select spore forming hydrogen producing bacteria like Clostridium sp. Experiments were conducted at different initial total sugar concentrations TS0 = 13 ± 1 g/L, 17 ± 1 g/L, 27 ± 3 g/L under thermophilic conditions (55 °C) for all particle types. The highest hydrogen yield (YH2 = 1.96 mol H2/mol glucose) and maximum hydrogen production rate (HPR = 7.39 ml H2/h) were obtained with polyester fiber particles at TS0 = 13 ± 1 g/L. The particle size of polyester fiber was varied between Dp = 0.5–3 cm at TS0 = 13 ± 1 g/L. The highest production yield of 1.96 mol H2/mol glucose was obtained with particle size of Dp = 1.5 cm. The results indicated that polyester fiber can be used as microorganism support particle for hydrogen production in immobilized bioprocesses.

Kinetic Models and Effects of Initial Total Soluble Sugar Concentrations on Batch Ethanol Fermentation of Sweet Sorghum Stalk Juice by Saccharomyces cerevisiae Strain

Effects of initial total soluble sugar concentrations on batch ethanol fermentation of sweet sorghum stalk juice by Saccharomyces cerevisiae strain were investigated at initial total soluble sugar concentrations of 85–156 g/L. The result showed that cell growth and the ethanol yield were increased with the increase of initial total soluble sugar concentrations. The kinetic parameters at initial total soluble sugar concentrations of 85–156 g/L were obtained. With the increase of initial total soluble sugar concentration, an inhibition of initial total soluble sugar concentration on the maximum specific growth rate (μmax) was observed. However, the increase of initial total soluble sugar concentration favors in the increase of the maximum specific ethanol production rate (qmax). The models proposed by Hinshelwood were found to be appropriate for describing the batch growth and ethanol fermentation of sweet sorghum stalk juice by immobilized Saccharomyces cerevisiae at initial total soluble sugar concentrations of 85–156 g/L because the correlation coefficients for the cell growth kinetic model and the ethanol production kinetic model were greater than 0.99.

Enhanced l-lysine production from pretreated beet molasses by engineered Escherichia coli in fed-batch fermentation

Faster sugar consumption rate and low-cost nitrogen source are required for the chemical biosynthesis using molasses. Five pretreatment methods were applied to beet molasses prior to fermentation through engineered Escherichia coli, respectively, and corn steep liquid was used as an organic nitrogen source to replace expensive yeast extract. Furthermore, the effects of different feeding strategy in fed-batch fermentation on L-lysine production were investigated. The experimental results showed that combined tricalcium phosphate, sulfuric acid, and activated carbon pretreatment method (TPSA) pretreatment could improve the sugar consumption rate most greatly, and the initial total sugar concentration of 35 g/L from TPSA-pretreated beet molasses gave the best results with respect to L-lysine production, dry cell weight concentration, and L-lysine yield in batch fermentation. Moreover, a mixture of low-cost corn steep liquid and yeast extract containing equal amount of nitrogen could be used as the organic nitrogen source for effective L-lysine fermentation, and constant speed feeding strategy of TPSA-pretreated beet molasses promoted L-lysine production by engineered E. coli. The TPSA-pretreated beet molasses had a sugar consumption rate of 1.75 g/(L h), and a L-lysine yield of 27.81% was achieved, compared with the theoretical yield of 62% by glucose. It was clarified that the pretreatment significantly enhanced the conversion of sugars in beet molasses to L-lysine.

Kinetic Modeling of Ethanol Batch Fermentation by Escherichia Coli FBWHR Using Hot-Water Sugar Maple Wood Extract Hydrolyzate as Substrate

A recombinant strain of Escherichia coli FBWHR was used for ethanol fermentation from hot-water sugar maple wood extract hydrolyzate in batch experiments. Kinetic studies of cell growth, sugar utilization and ethanol production were investigated at different initial total sugar concentrations of wood extract hydrolyzate. The highest ethanol concentration of 24.05 g/L was obtained using an initial total sugar concentration of 70.30 g/L. Unstructured models were developed to describe cell growth, sugar utilization and ethanol production and validated by comparing the predictions of model and experimental data. The results from this study could be expected to provide insights into the process performance, optimize the process and aid in the design of processes for large-scale production of ethanol fermentation from woody biomass.

Effects of temperature and substrate concentration on lipid production by Chlorella vulgaris from enzymatic hydrolysates of lipid-extracted microalgal biomass residues (LMBRs).

The enzymatic hydrolysates of the lipid-extracted microalgal biomass residues (LMBRs) from biodiesel production were evaluated as nutritional sources for the mixotrophic growth of Chlorella vulgaris and lipid production at different temperature levels and substrate concentrations. Both parameters had a significant effect on cell growth and lipid production. It was observed that C. vulgaris could grow mixotrophically in a wide range of temperatures (20∼35°C). The optimal temperature for cell growth and lipid accumulation of the mixotrophic growth of C. vulgaris was between 25 and 30°C. The neutral lipids of the culture at 25°C accounted for as much as 82% of the total lipid content in the microalga at culture day 8. Fatty acid composition analysis showed that the increase of saturated fatty acids was proportional to the increase in temperature. The maximum biomass concentration of 4.83g/L and the maximum lipid productivity of 164mg/L/day were obtained at an initial total sugar concentration of 10g/L and an initial total concentration of amino acids of 1.0g/L but decreased at lower and higher substrate concentrations. The present results show that LMBRS could be utilized by the mixotrophic growth of C. vulgaris for microalgal lipid production under the optimum temperature and substrate concentration.

Economical production of poly(ε-l-lysine) and poly(l-diaminopropionic acid) using cane molasses and hydrolysate of streptomyces cells by Streptomyces albulus PD-1.

Poly(ε-L-lysine) (ε-PL) and poly(L-diaminopropionic acid) (PDAP) co-production by Streptomyces albulus PD-1 from cane molasses and hydrolysate of strepyomyces cells (HSC) was investigated for the first time in this study. The optimal initial total sugar concentration of the cane molasses pretreated with sulfuric acid was determined to be 20 g L(-1), and HSC could substitute for yeast extract for ε-PL and PDAP co-production. When fed-batch fermentation was performed in 1t fermentor with pretreated cane molasses and HSC, 20.6 ± 0.5 g L(-1) of ε-PL and 5.2 ± 0.6 g L(-1) of PDAP were obtained. The amount of strepyomyces cells obtained in one fed-batch fermentation is sufficient to prepare the HSC to satisfy the demand of subsequent fermentations, thus the self-cycling of organic nitrogen source becomes available. These results suggest that the low-cost cane molasses and HSC can be used for the economical production of ε-PL and PDAP by S. albulus PD-1.

Optimization of citric acid production from a carrot juice-based medium by Yarrowia lipolytica using response surface methodology

In this study, diluted and fortified carrot juice was used for modelling and optimization of citric acid production by a new mutant strain, Yarrowia lipolytica K-168. Protein concentrate obtained from fine flour -a byproduct of semolina production- was used as a nitrogen source in the fermentation medium. Interactive effects of selected independent variables, initial total sugar concentration, initial pH, initial concentration of protein concentrate obtained from fine flour of semolina and temperature, on the growth and citric acid production of the yeast were investigated. An experimental design including 30 experiments was conducted by using the method of central composite design. Modelling the effects of these independent variables on maximum citric acid concentration, maximum citric acid production rate, citric acid yield, the ratio of maximum citric acid concentration to maximum isocitric acid concentration and specific growth rate were performed by response surface methodology. The variations of all of the responses with the independent variables were defined by a quadratic model. Numeric optimization was performed by using the desireability function. The conditions with 190.83 g/L initial sugar concentration, 5.90 initial pH, 0.07 g/L initial concentration of fine flour protein concentrate and 27.86 °C were determined as optimal conditions for citric acid production. The maximum citric acid concentration reached to 80.53 g/L in optimal conditions.