Fermentation of starch to ethanol by a complementary mixture of an amylolytic yeast andSaccharomyces cerevisiae

Summary Synergistic coculture of an amylolytic yeast (Saccharomycopsis fibuligera) andS. cerevisiae, a non-amylolytic yeast, fermented unhydrolyzed starch to ethanol with conversion efficiencies over 90% of the theoretical maximum. Fermentation was optimal between pH 5.0 to 6.0. Using a starch concentration of 10% (w/v) and a 5% (v/v) inoculum ofS. fibuligera, increasingS. cerevisiae inoculum from 4% to 12% (w/v) resulted in 35–40% (w/v) increase in ethanol yields. Anaerobic or limited aerobic incubation almost doubled ethanol yields.     

Kinetics of repeated batch production of ethanol by immobilized growing yeast cells

Summary Kinetic and yield parameters for growth and ethanol production from sucrose (100 g/l) bySaccharomyces cerevisia entrapped in K-carrageenan and calcium alginate were identical to those of free cells. Cell leakage was minimum with calcium alginate gel. For the sixth batch, 4.51 g/lh ethanol productivity (94% conversion of sucrose) was obtained; 60.5 g/l of ethanol was obtained from 200 g/l sucrose with 83.2% conversion, indicating inhibition effects.     

Ethanol production from sucrose by immobilizedZymomonas mobilis cells in polyurethane foam

Summary The possibility of using polyurethane foam as a support for the immobilization ofZymomonas mobilis cells to carry out sucrose conversion to ethanol was investigated. Sucrose hydrolysis efficiencies of 90% and higher, volumetric reactor productivity of 20 gL^–1h^–1 and final ethanol concentration of 6.3% (v/v) at a dilution rate of 0.4 h^–1 show the good performance of polyurethane foams for whole cell immobilization.     

Use of high-ethanol-resistant yeast isolates from Nigerian palm wine in lager beer brewing

High-ethanol-resistant yeasts, characterized as Saccharomyces sp., were isolated from Nigerian palm wine with added sucrose for high gravity brewing. The yeast isolates that survived the highest ethanol production were used to ferment brewery wort and produced 8.2 to 8.5% (v/v) ethanol; values almost double that of the control yeast from a local brewery.     

Selection of yeast able to produce ethanol from glucose at 40° C

Summary A total of 55 yeast strains selected from 7 genera known to ferment carbohydrates to ethanol were screened for their ability to ferment glucose to ethanol in shaken flask culture at 37°, 40° and 45°C. Yields of more than 50% of the theoretical maximum were obtained with 28 strains at 37°C, but only 12 at 40°C. Only 6 could grow at 45°C, but they produced poor yields. In general Kluyveromyces strains were more thermotolerant than Saccharomyces and Candida strains, but Saccharomyces strains produced higher ethanol yields. The 8 strains with the highest yields at 40°C were evaluated in batch fermentations. Three of these, two Saccharomyces and one Candida, were able to meet minimum commercial targets set at 8% (v/v) ethanol from 14% (w/v) glucose at 40°C.     

Top and bottom yeasts together accelerate ethanol production in molasses fermentation

Summary Alcohol producing top and bottom yeasts were employed individually and together to assess their role in enhancing the rate of ethanol production, in cane molasses fermentation, at 30°C. The combination of top yeastS.cerevisiae NCIM 3281, and bottom yeastS.uvarum NCIM 3509, improved the enthanol production rate by 32.6% in batch fermentation and 25.2% in recycling yeasts cell fermentation as compared to their mean value of individual ethanol production activity.     

Adaptation of Candida shehatae and Pichia stipitis to wood hydrolysates for increased ethanol production

Summary Candida shehatae ATCC 22984 and Pichia stipitis CBS 5776 were tested for ethanol production from xylose, glucose-xylose mixtures, and aspen wood total hydrolysates. Adaptation of these yeasts to wood hydrolysate solutions by recycling resulted in improved substrate utilization and ethanol production. Compared to the non-adapted cultures, recycled C. shehatae and P. stipitis in aspen hydrolysate increased g ethanol/g sugar consumed from 0.39 and 0.41 to 0.45 and 0.47; while ethanol production from a 70:30 glucose-xylose solution (total sugars 140 g/L) was 45 g/L in 24 h and 60 g/L in 72 h with the adapted yeasts compared to 15 g/L and 28 g/L in the same times with the parent strains.     

Ethanol production by Zymomonas mobilis CP4 from sugar cane chips

Summary The fermentation of large sugar cane chips (1.0–1.5 in) to ethanol by Zymomonas mobilis CP4 (Z. mobilis) was studied in two glass fermentors operating with culture circulation for agitation (the EX-FERM type): a. A laboratory scale(2.5 liter) cylindrical vessel; b. A bench scale (8 liter) wide vessel. Z. mobilis cultures consumed 89–96% of the cane sucrose, converting it to ethanol by 90–97% of the theoretical yield in the laboratory scale fermentor and by 83–90% in the bench scale fermentor culture. Comparative Saccharomyces spp. cultures in laboratory fermentor consumed 96–98% of the cane sucrose, with ethanol conversion of only 75–79% of the theoretical yield.These preliminary results indicated that sucrose in agricultural size sugar cane chips was ethanol fermentable as compared to small size sugar cane chips or to sugar cane juice. Z. mobilis CP4 cultures converted sucrose more efficiently to ethanol than Saccharomyces spp. as shown in the laboratory scale fermentor studies.The ethanol yields in a wide bench scale fermentor cultures were slightly lower than in a laboratory fermentor.     

Production of ethanol and biomass from various carbohydrates byKluyveromyces fragilis

Summary Growth ofKluyveromyces fragilis NRC 2475 and the production of ethanol by the yeast were studied in the media containing one of the following sugars: glucose, lactose, galactose, or a glucose-galactose (50% 50%) mixture as a carbon source.The largest biomass yield and the lowest yield of ethanol were obtained in the medium containing glucose. The medium containing galactose gave the lowest yield of biomass and the largest yield of ethanol. When lactose was used for the growth and production of ethanol the obtained results for both biomass and ethanol were between those obtained with glucose and galactose.The ethanol productivities, expressed in terms of ethanol produced either per unit of cells, or per unit of cells and time, were the highest in the system with galactose and the lowest in that with glucose.     

Role of antimicrobial agents in simultaneous saccharification and fermentation of paddy malt mash to ethanol by mixed cultures of Saccharomyces cerevisiae PH03 and Zymomonas mobilis ZM4

Summary Among various antimicrobial plant extracts, chemicals and antibiotics used for simultaneous saccharification and fermentation, penicillin G prevented contamination and did not inhibit amylase activity and growth of the synergistic co-cultures Saccharomyces cerevisiae PH03 and Zymomonas mobilis ZM4 during a 7-day fermentation of paddy malt (25.0%) mash (18.0% dextrose equivalent) to ethanol at 30°C and pH 5.5. The treatment yielded 10.1% (v/v) ethanol from the mash which was significantly more than that of the boiled and fermented mash (9.3% v/v) and equal to that of the mash boiled and fermented (10 2% v/v) after added amylases treatment. Most of the other compounds (kanamycin, streptomycin, polymyxin, tetracycline) had growth inhibitory effect especially on Z.mobilis.     

Fermentation capabilities ofZymomonas mobilis glycolytic enzymes

Summary Cell-free extracts ofZymomonas mobilis were capable of fermenting glucose to ethanol and CO₂ when stimulated by arsenate to act as an ATP uncoupler. 2M glucose was completely converted resulting in a final concentration of 16.5 % w/v ethanol. 1 M glucose was completely converted at temperatures up to 50°C. The results demonstrate that the glycolytic enzymes are more resistant to temperature and ethanol than are the living cells.     

Ethanol and biomass from Palmyra palm sap

Summary A strain ofSaccharomyces cerevisiae, Y18, has been isolated and characterized for the production of ethanol and biomass from the sap of Palmyra palm. The ethanol and biomass produced by Y18 in batch cultures without aeration were 70 g/L and 6 g/L respectively, from saps containing 150 g/L of sucrose. Under aerobic conditions, the biomass produced was 0.5 g/g sucrose, with crude and true protein contentsentrations of 57 and 52 % w/w respectively.     

The isomaltulose synthesising enzyme ofSerratia plymuthica

Summary An intracellular enzyme was located inSerratia plymuthica which produced isomaltulose from sucrose. The enzyme was purified giving a preparation with a specific activity of 1,285. It has pH and temperature optima of 6.0 and 30°C, respectively. The enzyme was stable retaining 100% activity after 2 weeks at 30°C. It had an isoelectric point at pH 9.0, a Mr of 79,500 and the Km for sucrose was 65.3mM. The enzyme converted 40% (w/v) sucrose to isomaltulose with an efficiency of 87%.     

High ethanol yields using Aspergillus oryzae koji and corn media

Summary High ethanol and stillage solids have been achieved using whole corn mashes. Ethanol yields of 14% (v/v) (89.5% of theory) and stillage levels of approximately 23% (w/v) were obtained in 74–90 hours using mild acid pretreatment with Aspergillus oryzae wheat bran koji saccharification. High ethanol yields were also obtained with bacterial amylase, instead of the acid treatment, when the sterilization step was omitted. The implications of ethanol fermentation process modifications are explored.     

Effect of temperature on sucrose to ethanol conversion by Zymomonas mobilis strains

Summary Two strains of Zymomonas mobilis were tested for their ability to ferment sucrose to ethanol at elevated temperatures (30–42.5°C). The optimal temperature for efficient sucrose to ethanol conversion was 35°C with 22–27 h fermentation time and 75% conversion efficiency. Increases in magnesium concentration improved one of the strains at 40°C from 38 to 76% ethanol yield efficiency.     

Could the improvements in the alcoholic fermentation of high glucose concentrations by yeast immobilization be explained by media supplementation?

Summary The maximal concentration of ethanol produced during the fermentation of 320 g/l glucose bySaccharomyces bayanus was higher when the yeast cells were immobilized either by adsorption on celite or by entrapment in k-carrageenan beads (from 10.5% with free cells up to 14.5% and 13.1% (v/v) respectively). This increase was due to medium supplementation with the compounds present in the immobilization supports.     

The kinetics of ethanol production by Zymomonas mobilis on fructose and sucrose media

Summary Z.mobilis is strain ZM4 was grown on 250 g/l fructose and sucrose media in batch culture and on 100 and 150 g/l sucrose media in continuous culture. With fructose, a significant reduction in the growth rate and the cell yield was apparent although the other kinetic parameters were similar to those previously reported for fermentation of glucose. With sucrose the major differences were a reduction in ethanol yield, (due to levan formation) and a lower final ethanol concentration. Ethanol inhibition of sucrose metabolism occurred at relatively low ethanol concentrations compared to those inhibiting glucose metabolism.     

Conversion of cellobiose and xylose to ethanol by immobilized growing cells of Clostridium saccharolyticum on charcoal support

Summary An immobilization technique has been developed for the conversion of both cellobiose and xylose to ethanol, which may be considered as one stage of a process for the conversion of cellulosic biomass to ethanol. Relatively inexpensive charcoal was used as a support material, with 23 mg dry weight of Clostridium saccharolyticum cells per g dry weight of support. Tests were run for 170 h at 0.15 1/h dilution rate. From a 3% (w/v) sugar mixture, 0.7% (w/v) ethanol was obtained with over 97% cellobiose and 62% xylose utilization.     

The inhibitory effect of ethanol on ethanol production by Zymomonas mobilis

Summary In an effort to establish the reasons for the limitations in the final ethanol concentration of Zymomonas mobilis fermentation, the effects of CO₂ and ethanol on the fermentation were investigated using continuous and fed-batch cultivation systems. The nucleation and stripping out of CO₂ from the fermenter using diatomaceous earth or nitrogen gas or both exhibited a profound effect on the glucose uptake rate during the early stages of fed-batch fermentation, but did not improve final ethanol yields. The addition of ethanol together with above mentioned experiments confirmed conclusively that ethanol inhibition is responsible for the final ethanol concentration obtainable during Zymomonas mobilis fermentation. The final concentration lies between 90 and 110 gl⁻¹ or approximately 12–15% (v/v) ethanol.     

Continuous production of ethanol from a glucose,xylose and arabinose mixture by a flocculent strain ofPichia stipitis

Summary Enhanced rates of continuous ethanol production by a flocculent strain ofPichia stipitis from a sugar mixture (xylose 75%, glucose 20%, arabinose 5%) were attained using a single-stage gas lift tower fermentor. With a substrate feed of 50g/l, the biomass accumulated at a level near 50g/l, showed a maximum and stable ethanol productivity of 10.7 g/l.h, with a substrate conversion of 80%; the ethanol yield reached 0.41g/g. In these operating conditions, similar performances were obtained when D.xylose alone was supplied.