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Lactic acid bacteria are widely used because they produce lactic acid naturally, are resistant to acidic pH and a wide temperature range, and frequently produce lactic acid as a primary metabolite. In this study, Enterococcus durans isolated from buffalo milk was employed in lactic acid fermentation with the primary goal of obtaining fermentation parameters for an effective process enabling the use of lactose as an alternative carbon source. Fermentative parameters such as initial concentration of carbon source, dissolved oxygen concentration, cell recycling, and batch with pulse operation mode were studied to find the best conditions for L-(+)-lactic acid production. The association of 20 g·L−1 of lactose with 10 g·L−1 of glucose enabled the best bioconversion to lactic acid. Anaerobiosis did not contribute to increasing lactic acid production. Batch fermentation with cell recycling was the strategy that enhanced lactic acid production and lactose consumption, reaching 26.07 g·L−1, 0.36 g·L−1 ·h−1 of productivity and yielding about 0.86 g·g−1. It is fundamental to evaluate the parameters of lactic acid fermentation and provide efficient and sustainable production methods. [ABSTRACT FROM AUTHOR]

Industrial production of ethanol by fermentation using renewable feedstock such as sugarcane stalks has been demonstrated as a sustainable fuel chain in Brazil. This work focused on the production of cellulosic ethanol from sugarcane bagasse in a pilot scale unit by applying the current bioprocessing strategies with the aim of recovering and characterizing the end products. The feedstock was pretreated at 190 °C and a residence time of 10 min. Enzymatic hydrolysis was performed with commercial cellulolytic enzymes. Fermentation's substrates were formulated with hydrolysate and supplemented with 8%wt sugarcane molasses. The fermentations were set up to mimic the conventional industrial fermentation in Brazil's ethanol distilleries at high cell density with cell recycling. The fermentation resulted in a reproducible performance by the yield of 0.49 g/g, productivity of 6.96 g/(L∙h), and cell viability of 95.3%. Ethanol was recovered in a lab-scale distillation batch system. Distilled fractions showed higher content of higher alcohols and sulfur content than the standard specification of ANP (National Agency of Petroleum - Brazilian Agency) for ethanol fuel. The distillation bottom product (vinasse) presented most characteristics suitable for fertilizer or biogas applications, except for sodium and sulfate content. Therefore, for a successful technology, transference processing adjustments should be made to make the product commercially suitable and the side stream compatible for disposal as fertilizer or digestion for biogas production. • Experimental evaluation of production of ethanol from sugarcane bagasse hydrolysate. • Production of hydrolysate in a pilot scale reactor and saccharification with commercial hydrolytic enzymes. • Hydrolysate conditioned by clarification process and nutrients supplementation with 8% wt of sugarcane molasses. • Fermentation with an industrial yeast Saccharomyces cerevisiae at high cell density and recycling in a fed-batch mode. • Characterization of the recovered ethanol showed a noticeable amount of higher alcohols (propanol and 2-Methyl-1-propanol). • The bottom distillation product presented higher salts content and organic matter than the current ethanol process. [ABSTRACT FROM AUTHOR]

Abstract The Very High Gravity (VHG) fermentation is a technology that can lead to a reduction in waste generation, a reduction in energy consumption and GHG emissions and several technical, economic, and environmental advantages. Having, as a limiting factor, yeast tolerance to the most diverse stressors in the fermentation medium. To overcome this limitation, the aim of the work was to verify the potential protective effect of silica (+A) on Saccharomyces cerevisiae (Ethanol Red®) submitted to VHG fermentation. Initially, an adaptive test to VHG fermentation was carried out, with 5 cell recycles in musts from sugar cane syrup. Each recycle was subjected to the treatments, in quadruplicate: T1C (control) - Wort without silica supplementation; T2S100- Wort with supplementation of 100 mg L-1 of silica and T3S300- Wort with supplementation of 300 mg L -1 of silica. As a result, the T3S300 treatment in the adaptive test, showed viability of 77.5 to 81.55%; biomass production from 8.1 to 10.0 g L-1; yield from 90.0 to 95.3% and productivity from 7.3 to 10.9 mL L-1h-1. In conclusion, the treatment of the wort with silica (+A) (100 and 300 mg L-1) has an effect protector on yeast and may present positive responses in VHG fermentations.

Lactic acid bacteria are widely used because they produce lactic acid naturally, are resistant to acidic pH and a wide temperature range, and frequently produce lactic acid as a primary metabolite. In this study, Enterococcus durans isolated from buffalo milk was employed in lactic acid fermentation with the primary goal of obtaining fermentation parameters for an effective process enabling the use of lactose as an alternative carbon source. Fermentative parameters such as initial concentration of carbon source, dissolved oxygen concentration, cell recycling, and batch with pulse operation mode were studied to find the best conditions for L-(+)-lactic acid production. The association of 20 g·L−1 of lactose with 10 g·L−1 of glucose enabled the best bioconversion to lactic acid. Anaerobiosis did not contribute to increasing lactic acid production. Batch fermentation with cell recycling was the strategy that enhanced lactic acid production and lactose consumption, reaching 26.07 g·L−1, 0.36 g·L−1·h−1 of productivity and yielding about 0.86 g·g−1. It is fundamental to evaluate the parameters of lactic acid fermentation and provide efficient and sustainable production methods.

Poly(β-L-malic acid) (PMLA) is a water-soluble, biodegradable, and biocompatible polymer with broad prospective applications and can be hydrolyzed to produce widely used acidulant L-malic acid. In order to meet an increasing demand of PMLA, we employed two effective cell-recycling strategies to produce PMLA from raw cassava hydrolysate by Aureobasidium pullulans ZD-3d. In fed-batch fermentation with raw cassava hydrolysate, 101.9 g/L PMLA was obtained with the productivity and yield of 0.77 g/L/h and 0.40 g/g, respectively. Further, three times of membrane filtration–based cell recycling fermentation was carried out, with a high productivity and yield of 1.04–1.64 g/L/h and 0.5–0.84 g/g achieved, respectively. While harnessing centrifugation-based cell recycling fermentation for five times, the productivity and yield approached 0.98–1.76 g/L/h and 0.78–0.86 g/g, respectively. To our knowledge, the processes showed the highest average PMLA productivity compared with others using low-cost biomass, which offered efficient and economical alternatives for PMLA production. Key points: • PMLA production from raw cassava hydrolysate by Aureobasidium pullulans was studied • High PMLA productivity and yield were obtained via two cell recycling strategies • The highest average PMLA productivity from low-cost biomass to date was achieved [ABSTRACT FROM AUTHOR]

BACKGROUND: Nitrosomonas eutropha is a chemolithoautotrophic organism with an ability to oxidize ammonium to nitrite and nitrate. Continuous culture with and without cell recycling was used to enhance production of N. eutropha cell biomass using a 40‐L bioreactor. Whole cell biotransformation was used to convert methane (CH4) present in the biogas into biomethanol using N. eutropha. RESULTS: The maximum biomass production rate of N. eutropha was increased by three‐fold with provision of cell recycling in the continuous culture. Removal of nitrite from the continuous culture resulted in high activity of ammonia monooxygenase enzyme responsible for conversion of CH4 to biomethanol. Use of ammonium sulfate as a source of electrons for biotransformation reaction with N. eutropha resulted in a maximum 119.86 mg L−1 of biomethanol production. CONCLUSION: Our research provides an efficient process for biomass production of N. eutropha using continuous culture. We have demonstrated improvement in CH4 to biomethanol conversion using biogas as feedstock. © 2021 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The presence of toxic degradation products in lignocellulosic hydrolysate typically reduced fermentation rates and xylose consumption rate, resulting in a decreased ethanol productivity. In the present study, Zymomonas mobilis 8b was investigated for high cell density fermentation with cell recycling to improve the ethanol productivity in lignocellulosic hydrolysate. The fermentation performances of Z. mobilis 8b at various conditions were first studied in yeast extract-tryptone medium. It was found that nutrient level was essential for glucose and xylose co-fermentation by Z. mobilis 8b and high cell density fermentation with cell recycling worked well in yeast extract-tryptone medium for 6 rounds fermentation. Z. mobilis 8b was then studied in enzymatic hydrolysates derived from dilute acid (DA) pretreated corn stover (CS) and ammonia pretreated CS for high cell density fermentation with cell recycling. Ethanol productivity obtained was around three times higher compared to traditional fermentation. Ethanol titer and metabolic yield were also enhanced with high cell density fermentation. Z. mobilis 8b cells showed high recyclability in ammonia pretreated CS hydrolysate.

The available pneumococcal conjugate vaccines provide protection against only those serotypes that are included in the vaccine, which leads to a selective pressure and serotype replacement in the population. An alternative low-cost, safe and serotypeindependent vaccine was developed based on a nonencapsulated pneumococcus strain. This study evaluates process intensification to improve biomass production and shows for the first time the use of perfusion-batch with cell recycling for bacterial vaccine production. Batch, fed-batch, and perfusion-batch were performed at 10 L scale using a complex animal component-free culture medium. Cells were harvested at the highest optical density, concentrated and washed using microfiltration or centrifugation to compare cell separation methods. Higher biomass was achieved using perfusion-batch, which removes lactate while retaining cells. The biomass produced in perfusion-batch would represent at least a fourfold greater number of doses per cultivation than in the previously described batch process. Each strategy yielded similar vaccines in terms of quality as evaluated by western blot and animal immunization assays, indicating that so far, perfusion-batch is the best strategy for the intensification of pneumococcal whole-cell vaccine production, as it can be integrated to the cell separation process keeping the same vaccine quality. [ABSTRACT FROM AUTHOR]

The production of Brazilian ethanol has aroused worldwide interest, since it is made from a source of renewable biomass, sugarcane and yeast metabolism. Thus, the objective of this study is to compare the characteristics of sugarcane and sorghum biomass and to evaluate the ethanol and glycerol production of yeast FT-858 in different culture conditions. An exploratory qualitative bibliographical study was performed regarding the technological characteristics of saccharine substrates. A pre-inoculum using sterile liquid medium YPD 2% was prepared, in which 0.10 g of FT-858 yeast was inoculated and incubated at 30 ° C for 10h at 250rpm. Cells were collected by centrifugation and inoculated in the fermentation medium based on sugarcane and sorghum at the concentration of 22 ° Brix. The process was carried out by cellular recycling and inoculated into the substrate at 30 and 40 ° C at 250rpm. Aliquots of 4 ml were collected for intracellular glycerol analysis via enzymatic kit and ethanol concentration by gas chromatography. It can be observed that both substrates have a similar composition in relation to sugars, although the sugarcane juice has a higher sucrose. The accumulation of intracellular glycerol was more significant in the cane juice at both temperatures and the ethanol concentration decreased throughout the recycle. [ABSTRACT FROM AUTHOR]

The presence of toxic degradation products in lignocellulosic hydrolysate typically reduced fermentation rates and xylose consumption rate, resulting in a decreased ethanol productivity. In the present study, Zymomonas mobilis 8b was investigated for high cell density fermentation with cell recycling to improve the ethanol productivity in lignocellulosic hydrolysate. The fermentation performances of Z. mobilis 8b at various conditions were first studied in yeast extract-tryptone medium. It was found that nutrient level was essential for glucose and xylose co-fermentation by Z. mobilis 8b and high cell density fermentation with cell recycling worked well in yeast extract-tryptone medium for 6 rounds fermentation. Z. mobilis 8b was then studied in enzymatic hydrolysates derived from dilute acid (DA) pretreated corn stover (CS) and ammonia pretreated CS for high cell density fermentation with cell recycling. Ethanol productivity obtained was around three times higher compared to traditional fermentation. Ethanol titer and metabolic yield were also enhanced with high cell density fermentation. Z. mobilis 8b cells showed high recyclability in ammonia pretreated CS hydrolysate. [ABSTRACT FROM AUTHOR]

Polyhydroxyalkanoates (PHA) are microbial biopolyesters utilized as "green plastics". Their production under controlled conditions resorts to bioreactors operated in different modes. Because PHA biosynthesis constitutes a multiphase process, both feeding strategy and bioreactor operation mode need smart adaptation. Traditional PHA production setups based on batch, repeated batch, fed-batch or cyclic fed-batch processes are often limited in productivity, or display insufficient controllability of polyester composition. For highly diluted substrate streams like is the case of (agro) industrial waste streams, fed-batch enhanced by cell recycling has recently been reported as a viable tool to increase volumetric productivity. As an emerging trend, continuous fermentation processes in single-, two- and multi-stage setups are reported, which bring the kinetics of both microbial growth and PHA accumulation into agreement with process engineering and allow tailoring PHA's molecular structure. Moreover, we currently witness an increasing number of CO2-based PHA production processes using cyanobacteria; these light-driven processes resort to photobioreactors similar to those used for microalgae cultivation and can be operated both discontinuously and continuously. This development is parallel to the emerging use of methane and syngas as abundantly available gaseous substrates, which also calls for bioreactor systems with optimized gas transfer. The review sheds light on the challenges of diverse PHA production processes in different bioreactor types and operational regimes using miscellaneous microbial production strains such as extremophilic Archaea, chemoheterotrophic eubacteria and phototrophic cyanobacteria. Particular emphasis is dedicated to the limitations and promises of different bioreactor-strain combinations and to efforts devoted to upscaling these processes to industrially relevant scales. [ABSTRACT FROM AUTHOR]

The major bottleneck in industrial alcoholic fermentation is inhibition by the product, which limits the ethanol yield and productivity. An efficient way of overcoming this problem is to use gas stripping to remove the ethanol during the process. In this work, the production of ethanol from sugarcane using extractive continuous fermentation with CO 2 stripping was modeled and simulated. The ethanol stripping performance was first evaluated experimentally, varying the specific CO 2 flow rate (ϕ CO 2 ), the solution temperature (T sol ), and the initial ethanol concentration (C E0 ). The parameters ϕ CO 2 and T sol showed positive influences on the stripping kinetics. The proposed CO 2 stripping model considered the removal of ethanol and water, as well as changes in the solution volume, and was able to accurately describe the process. Modeling and simulation of the continuous fermentation were performed considering different conditions of feed substrate concentration and cell recycling. The results indicated that ethanol inhibition could be alleviated by CO 2 stripping. In addition, the combined use of stripping and cell recycling enabled the use of feed musts containing up to 400 g L −1 of sucrose, with high substrate conversion, ethanol productivity of 10.79 g L −1 h −1 , and total ethanol amount produced of 174.80 g L −1 (22.2°GL), which is about twice the value achieved in an industrial process without ethanol removal by CO 2 stripping. This strategy is very promising, compared to traditional processes used in Brazilian distilleries, and has the potential to reduce the global process costs, since it decreases the energy consumed for product recovery and allows the use of smaller fermenters. [ABSTRACT FROM AUTHOR]

2,2-Bis(hydroxymethyl)butyric acid (BHMB) is an important multifunctional chemical for the emerging bio-based polymer industry. It can be produced from trimethylolpropane (TMP) by selective oxidation using growing cells of Corynebacterium sp. ATCC 21245. However, this process is limited by the low volumetric productivity and low concentration of the final product. In the present study, we performed sequential batch operation with cell recycling in media containing glycerol, acetic acid, and increasing concentrations of yeast extract. This approach enhanced the conversion of 10 and 15 g/L TMP to 11.0 and 16.3 g/L BHMB at rates of 0.50 and 0.20 g/L . h, respectively. Applying a cell bleeding strategy resulted in an overall 10-fold improvement in productivity. The consequently prolonged biocatalyst viability resulted in a quantitative conversion of 20 g/L TMP to 22.3 g/L BHMB and a yield of 1.10 g BHMB /g TMP (100% molar yield). This work facilitates further studies of the selective oxidation on other industrially important polyols. [ABSTRACT FROM AUTHOR]

Although first-generation fuel ethanol is produced in Brazil from sugarcane-based raw materials with high efficiency, there is still little knowledge about the microbiology, the biochemistry and the molecular mechanisms prevalent in the non-aseptic fermentation environment. Learning-by-doing has hitherto been the strategy to improve the process so far, with further improvements requiring breakthrough technologies. Performing experiments at an industrial scale are often expensive, complicated to set up and difficult to reproduce. Thus, developing an appropriate scaled down system for this process has become a necessity. In this paper, we present the design and demonstration of a simple and effective laboratory-scale system mimicking the industrial process used for first generation (1G) fuel ethanol production in the Brazilian sugarcane mills. We benchmarked this system via the superior phenotype of the Saccharomyces cerevisiae PE-2 strain, compared to other strains from the same species: S288c, baker's yeast, and CEN.PK113-7D. We trust that such a system can be easily implemented in different laboratories worldwide, and will allow a better understanding of the S. cerevisiae strains that can persist and dominate in this industrial, non-aseptic and peculiar environment. [ABSTRACT FROM AUTHOR]

Polyhydroxyalkanoates (PHA) are microbial biopolyesters utilized as “green plastics”. Their production under controlled conditions resorts to bioreactors operated in different modes. Because PHA biosynthesis constitutes a multiphase process, both feeding strategy and bioreactor operation mode need smart adaptation. Traditional PHA production setups based on batch, repeated batch, fed-batch or cyclic fed-batch processes are often limited in productivity, or display insufficient controllability of polyester composition. For highly diluted substrate streams like is the case of (agro) industrial waste streams, fed-batch enhanced by cell recycling has recently been reported as a viable tool to increase volumetric productivity. As an emerging trend, continuous fermentation processes in single-, two- and multi-stage setups are reported, which bring the kinetics of both microbial growth and PHA accumulation into agreement with process engineering and allow tailoring PHA’s molecular structure. Moreover, we currently witness an increasing number of CO2-based PHA production processes using cyanobacteria; these light-driven processes resort to photobioreactors similar to those used for microalgae cultivation and can be operated both discontinuously and continuously. This development is parallel to the emerging use of methane and syngas as abundantly available gaseous substrates, which also calls for bioreactor systems with optimized gas transfer. The review sheds light on the challenges of diverse PHA production processes in different bioreactor types and operational regimes using miscellaneous microbial production strains such as extremophilic Archaea, chemoheterotrophic eubacteria and phototrophic cyanobacteria. Particular emphasis is dedicated to the limitations and promises of different bioreactor–strain combinations and to efforts devoted to upscaling these processes to industrially relevant scales.

Ethanol has provoked great interest due to its potential as an alternative fuel. Nevertheless, fermentation processes must be developed by increasing the low volumetric productivity achieved in conventional cultures (batch or continuous) to make this product become economically competitive. This can be achieved by using techniques leading to high cell concentration and reducing inhibition by the end-product. One of the frequently employed methods involves cell recycling. This work thus developed a membrane reactor incorporating a filtration module with 5 u,m stainless steel tubular units inside a 3L stirred jar fermenter for investigating its application in continuous ethanol production. The effects of cell concentration and transmembrane pressure difference on permeate flux were evaluated for testing the filtration module's performance. The internal cell retention system was operated in Saccharomyces cerevisiae continuous culture derived from sucrose, once fermentation conditions had been selected (30 °C, 1.25 -1.75 vvm, pH 4.5). Filter unit permeability was maintained by applying pulses of air. More than 97% of the grown cells were retained in the fermenter, reaching 51 g/L cell concentration and 8.51 g/L.h average ethanol productivity in culture with internal cell retention; this was twice that obtained in a conventional continuous culture. Key words: Membrane reactor, Saccharomyces cerevisiae, alcoholic fermentation, cell recycling.

Effects of degradation products (low molecular weight compounds produced during pretreatment) on the microbes used in the RaBIT (Rapid Bioconversion with Integrated recycling Technology) process that reduces enzyme usage up to 40% by efficient enzyme recycling were studied. Chemical genomic profiling was performed, showing no yeast response differences in hydrolysates produced during RaBIT enzymatic hydrolysis. Concentrations of degradation products in solution were quantified after different enzymatic hydrolysis cycles and fermentation cycles. Intracellular degradation product concentrations were also measured following fermentation. Degradation product concentrations in hydrolysate did not change between RaBIT enzymatic hydrolysis cycles; the cell population retained its ability to oxidize/reduce (detoxify) aldehydes over five RaBIT fermentation cycles; and degradation products accumulated within or on the cells as RaBIT fermentation cycles increased. Synthetic hydrolysate was used to confirm that pretreatment degradation products are the sole cause of decreased xylose consumption during RaBIT fermentations. [ABSTRACT FROM AUTHOR]

Background The Rapid Bioconversion with Integrated recycle Technology (RaBIT) process reduces capital costs, processing times, and biocatalyst cost for biochemical conversion of cellulosic biomass to biofuels by reducing total bioprocessing time (enzymatic hydrolysis plus fermentation) to 48 h, increasing biofuel productivity (g/L/h) twofold, and recycling biocatalysts (enzymes and microbes) to the next cycle. To achieve these results, RaBIT utilizes 24-h high cell density fermentations along with cell recycling to solve the slow/incomplete xylose fermentation issue, which is critical for lignocellulosic biofuel fermentations. Previous studies utilizing similar fermentation conditions showed a decrease in xylose consumption when recycling cells into the next fermentation cycle. Eliminating this decrease is critical for RaBIT process effectiveness for high cycle counts. Results Nine different engineered microbial strains (including Saccharomyces cerevisiae strains, Scheffersomyces (Pichia) stipitis strains, Zymomonas mobilis 8b, and Escherichia coli KO11) were tested under RaBIT platform fermentations to determine their suitability for this platform. Fermentation conditions were then optimized for S. cerevisiae GLBRCY128. Three different nutrient sources (corn steep liquor, yeast extract, and wheat germ) were evaluated to improve xylose consumption by recycled cells. Capacitance readings were used to accurately measure viable cell mass profiles over five cycles. Conclusion The results showed that not all strains are capable of effectively performing the RaBIT process. Acceptable performance is largely correlated to the specific xylose consumption rate. Corn steep liquor was found to reduce the deleterious impacts of cell recycle and improve specific xylose consumption rates. The viable cell mass profiles indicated that reduction in specific xylose consumption rate, not a drop in viable cell mass, was the main cause for decreasing xylose consumption. [ABSTRACT FROM AUTHOR]

The effects of both biomass age and cell recycling on the 1,3-propanediol (1,3-PDO) production by Klebsiella pneumoniae were investigated in a membrane-supported bioreactor using hollow-fiber ultrafiltration membrane module in two separate experiments. It was determined that older cells have a negative effect on 1,3-PDO production. The concentrations of by-products, such as acetic acid and ethanol, increased in cultures with older cells, whereas the concentrations of succinic acid, lactic acid and 2,3-butanediol decreased. The effect of cell recycling was comparatively studied at a cell recycling ratio of 100 %. The results showed that cell recycling had also negative effects on 1,3-PDO fermentation. It was hypothesized that both cell recycling and biomass age caused metabolic shifts to undesired by-products which then inhibited the 1,3-PDO production. On the other hand, the use of hollow-fiber ultrafiltration membrane module was found to be very effective in terms of removal of cells from the fermentation broth. [ABSTRACT FROM AUTHOR]

Abstract: Fermentative production of optically pure lactic acid has roused interest among researchers in recent years due to its high potential for applications in a wide range of fields. More specifically, the sharp increase in manufacturing of biodegradable polylactic acid (PLA) materials, green alternatives to petroleum-derived plastics, has significantly increased the global interest in lactic acid production. However, higher production costs have hindered the large-scale application of PLA because of the high price of lactic acid. Therefore, reduction of lactic acid production cost through utilization of inexpensive substrates and improvement of lactic acid production and productivity has become an important goal. Various methods have been employed for enhanced lactic acid production, including several bioprocess techniques facilitated by wild-type and/or engineered microbes. In this review, we will discuss lactic acid producers with relation to their fermentation characteristics and metabolism. Inexpensive fermentative substrates, such as dairy products, food and agro-industrial wastes, glycerol, and algal biomass alternatives to costly pure sugars and food crops are introduced. The operational modes and fermentation methods that have been recently reported to improve lactic acid production in terms of concentrations, yields, and productivities are summarized and compared. High cell density fermentation through immobilization and cell-recycling techniques are also addressed. Finally, advances in recovery processes and concluding remarks on the future outlook of lactic acid production are presented. [Copyright &y& Elsevier]

Highlights: [•] A cell recycling two-tank system was used for continuous production of bioethanol. [•] Each tank fermentor equipped with a settler for recycling of flocculent yeast. [•] The system was effective for ethanol production at high dilution rates. [•] The productivity was tremendously enhanced compared with batch fermentation. [ABSTRACT FROM AUTHOR]

Abstract: A continuous butanol production system with high-density Clostridium saccharoperbutylacetonicum N1-4 generated by cell recycling was established to examine the characteristics of butanol fermentation from xylose. In continuous culture without cell recycling, cell washout was avoided by maintaining pH>5.6 at a dilution rate of 0.26h−1, indicating pH control was critical to this experiment. Subsequently, continuous culture with cell recycling increased cell concentration to 17.4gL−1, which increased butanol productivity to 1.20gL−1 h−1 at a dilution rate of 0.26h−1 from 0.529gL−1 h−1 without cell recycling. The effect of dilution rates on butanol production was also investigated in continuous culture with cell recycling. Maximum butanol productivity (3.32gL−1 h−1) was observed at a dilution rate of 0.78h−1, approximately 6-fold higher than observed in continuous culture without cell recycling (0.529gL−1 h−1). [Copyright &y& Elsevier]

Fructooligosaccharide (FOS) production was carried out using fructosyl transferase (FTase) produced by Aspergillus oryzae CFR 202 under submerged fermentation conditions. The pellets of A. oryzae CFR 202 obtained after 48 h of fermentation were supplemented with fresh media after every 24 h and fermentation was carried out to produce FTase. FTase so obtained was used to produce FOS using 60% sucrose as substrate at 55 °C at pH 5.15. FTase activity was maintained in the range of 15 ± 2 U/ml/min up to six recycles. FOS yields were maintained at 53% up to 6th cycle. Recycling of pellets could not be carried out after 6th cycle due to disintegration. The system is advantageous and economical in that it does not require supplementation of any additional nutrients nor it requires the development of fresh inoculum. [Copyright &y& Elsevier]