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PubMed2005

Occurrence and diversity of yeasts involved in fermentation of West African cocoa beans.

Samples of cocoa beans were taken on two separate occasions during heap and tray fermentations in Ghana, West Africa. In total 496 yeast isolates were identified by conventional microbiological analyses and by amplification of their ITS1-5.8S rDNA-ITS2 regions. For important species the identifications were confirmed by sequencing of the D1/D2 domain of the 5' end of the large subunit (26S) rDNA. Assimilations of organic acids and other carbon compounds were conducted. For dominant yeasts intraspecies variations were examined by determination of chromosome length polymorphism (CLP) using pulsed-field gel electrophoresis. For the heap fermentations maximum yeast cell counts of 9.1 x 10(7) were reached, whereas maximum yeast counts of 6.0 x 10(6) were reached for the tray fermentations. Candida krusei was found to be the dominant species during heap fermentation, followed by P. membranifaciens, P. kluyveri, Hanseniaspora guilliermondii and Trichosporon asahii, whereas Saccharomyces cerevisiae and P. membranifaciens were found to be the dominant species during tray fermentation followed by low numbers of C. krusei, P. kluyveri, H. guilliermondii and some yeast species of minor importance. For isolates within all dominant species CLP was evident, indicating that several different strains are involved in the fermentations. Isolates of C. krusei, P. membranifaciens, H. guilliermondii, T. asahii and Rhodotorula glutinis could be found on the surface of the cocoa pods and in some cases on the production equipment, whereas the origin of e.g. S. cerevisiae was not indicated by the results obtained. In conclusion, the results obtained show that fermentation of cocoa beans is a very inhomogeneous process with great variations in both yeast counts and species composition. The variations seem to depend especially on the processing procedure, but also the season and the post-harvest storage are likely to influence the yeast counts and the species composition.

Africa, Western↗
PubMed2006

Functional genomic analysis of commercial baker's yeast during initial stages of model dough-fermentation.

Gene expression profiles of baker's yeast during initial dough-fermentation were investigated using liquid fermentation (LF) media to obtain insights at the molecular level into rapid adaptation mechanisms of baker's yeast. Results showed that onset of fermentation caused drastic changes in gene expression profiles within 15 min. Genes involved in the tricarboxylic acid (TCA) cycle were down-regulated and genes involved in glycolysis were up-regulated, indicating a metabolic shift from respiration to fermentation. Genes involved in ethanol production (PDC genes and ADH1), in glycerol synthesis (GPD1 and HOR2), and in low-affinity hexose transporters (HXT1 and HXT3) were up-regulated at the beginning of model dough-fermentation. Among genes up-regulated at 15 min, several genes classified as transcription were down-regulated within 30 min. These down-regulated genes are involved in messenger RNA splicing and ribosomal protein biogenesis and in transcriptional regulator (SRB8, MIG1). In contrast, genes involved in amino acid metabolism and in vitamin metabolism, such as arginine biosynthesis, riboflavin biosynthesis, and thiamin biosynthesis, were subsequently up-regulated after 30 min. Interestingly, the genes involved in the unfolded protein response (UPR) pathway were also subsequently up-regulated. Our study presents the first overall description of the transcriptional response of baker's yeast during dough-fermentation, and will thus help clarify genomic responses to various stresses during commercial fermentation processes.

Bread↗
PubMed2006

Liquid sourdough fermentation: industrial application perspectives.

Sourdough fermentation is considered to play a key role to get improved flavour, texture, nutritional and shelf-life properties of bakery products. Since few years Barilla R&D has been focusing on liquid sourdough fermentation which may deserve several advantages with respect to traditional processes. The results showed that the micro-biota of sourdough markedly influences flavour and texture of bakery products. Particular attention has been paid to lactic acid bacteria and yeasts. Selected lactic acid bacteria and yeasts were tested in sourdough liquid fermentation as single strain or in association. The parameters of fermentations were optimized and standardized to set up a laboratory plant liquid fermentation. Only a few strains of lactic acid bacteria were found to be suitable for liquid fermentation alone or in association with yeasts. Fermentations were carried out at pilot plant and an industrial technology was developed. This work describes the results found for the organoleptic profile of an industrial bread started with liquid sourdough with respect to bakers' yeast bread without sourdough addition.

Bioreactors↗
PubMed2004

Application of central composite design and response surface methodology to the fermentation of olive juice by Lactobacillus plantarum and Debaryomyces hansenii.

The objectives of this study were to investigate the effects of NaCl, calcium acetate and calcium lactate in concentrations corresponding to ionic strengths equivalent to 2-10%, w/v salt brines as well as the 50% replacement of NaCl contained in the above mixture by KCl. A central composite design and response surface methodology were used to optimize the maximum specific growth rate of Lactobacillus plantarum ATCC 8014 and Debaryomyces hansenii 2114. The fermentation was carried out in olive juice obtained from Kalamon black olives at 30 degrees C with initial pH 5.0. Mathematical models describing the combined effects of these factors on the maximum specific growth rate of L. plantarum or D. hansenii were established. Both strains in single cultures showed higher maximum specific growth rate in olive juice supplemented with NaCl/KCl, Ca-acetate and Ca-lactate. But in mixed culture fermentations of olive juice supplemented with NaCl, Ca-acetate and Ca-lactate, higher specific growth rates were obtained. Under the optimum growth conditions determined for the single culture fermentations, i.e. 378.4 mM NaCl, 34.1 mM Ca-acetate and 39.9 mM Ca-lactate, mixed culture fermentation was undertaken by varying the time of inoculation of the yeast strain. When D. hansenii was inoculated 48 h before L. plantarum the maximum specific growth rate of L. plantarum was increased to 0.247 per hour, which was significantly higher compared to L. plantarum alone (0.211 per hour). In mixed culture fermentation of olive juice supplemented with the mixture of NaCl/KCl under similar conditions as above, a maximum specific growth rate of L. plantarum of 0.218 per hour was determined. The optimum conditions determined for mixed culture fermentation are useful in fermentation of black olives Kalamon variety under lower salt content.

Acetates↗
PubMed2005

Characterisation of the microflora of attiéké, a fermented cassava product, during traditional small-scale preparation.

Attiéké is a fermented cassava product consumed mainly in Cote d'Ivoire. The aim of this study was to characterise the attiéké fermentation by examining products from 15 small-scale production sites at various stages of its preparation. For the preparation of attiéké, fresh cassava is grated to a pulp and inoculated with 10% of a spontaneous traditional inoculum. The inocula contained aerobic mesophiles at mean numbers of 8.2 x 10(7) cfu/g and lactic and acetic acids at mean concentrations of 0.2% and 0.1%, respectively. The mean pH was 5.0. Lactic acid bacteria were the dominant microorganisms in cassava pulp throughout fermentation with the mean numbers being 1.2 x 10(9) cfu/g after 15 h. The identification to the species level of microorganisms from one representative attiéké production of good quality showed that, at the start of fermentation, Leuconostoc mesenteroides subsp. mesenteroides was present in the highest numbers, accounting for 20% of all lactic acid bacteria. As the fermentation proceeded, this species was replaced by homofermentative lactic acid bacteria, Lactobacillus salivarius and Lactobacillus delbrueckii subsp. delbrueckii, present at 20% and 16%, respectively, and obligate heterofermentatives, Lactobacillus fermentum and Lactobacillus confusus at 12% and 10%, respectively, of total lactic acid bacteria in the flora at the end of fermentation. High numbers of acid-sensitive microorganisms, Bacillus circulans, Bacillus lentus, Enterobacter sakazakii, Enterobacter cloacae and Klebsiella pneumoniae subsp. pneumoniae, were transferred to the pulp in the inocula, but acidification to a mean pH of 4.4 with mean lactic and acetic acid concentrations of 0.59% and 0.2%, respectively, prevented their growth and reduced their numbers to less than 10(2) cfu/g at the end of fermentation. The mean numbers of Candida tropicalis, the main yeast present, remained relatively constant at about 10(5) cfu/g throughout attiéké production. The mean numbers of aerobic mesophiles decreased to below 10(2) cfu/g as a result of the steaming process. The finished attiéké had a mean pH of 4.4 and mean lactic and acetic acid concentrations of 0.6% and 0.1%, respectively.

Acetic Acid↗
PubMed2006

Influence of fermentation temperature on volatile thiols concentrations in Sauvignon blanc wines.

The effect of Saccharomyces cerevisiae strains on the amount of 4-mercapto-4-methylpentan-2-one, a major varietal aroma of Sauvignon blanc wines, was demonstrated by previous research work. However, the influence of different alcoholic fermentation parameters on the levels of volatile thiols (4-mercapto-4-methylpentan-2-one, 3-mercaptohexan-1-ol and 3-mercaptohexyl acetate) in wines has not yet been investigated. The impact of fermentation temperature on the final amount of volatiles thiols and on some other analytical parameters (ethanol, total acidity, residual sugars, volatile acidity) was determined in a model medium and in grape juice. Interaction between fermentation temperature and yeast strain was also tested. The fermentation temperature influenced the amount of volatile thiols irrespective of the yeast strain used. The final levels of 4MMP and 3MH in model medium and in wines were higher when the alcoholic fermentation is conducted at 20 degrees C than at 13 degrees C. The 3MHA, which was correlated with the amount of 3MH determined in wines, was also higher when the alcoholic fermentation was conducted at 20 degrees C. From a technological point of view, the choice of yeast strain and fermentation temperature has a decisive influence on the concentrations of the varietal aromas of Sauvignon blanc wines.

Fermentation↗
PubMed2006

Rapid screening of the fermentation profiles of wine yeasts by Fourier transform infrared spectroscopy.

A rapid screening method for the evaluation of the major fermentation products of Saccharomyces wine yeasts was developed using Fourier transform infrared spectroscopy and principal component factor analysis. Calibration equations for the quantification of volatile acidity, glycerol, ethanol, reducing sugar and glucose concentrations in fermented Chenin blanc and synthetic musts were derived from the Fourier transform infrared spectra of small-scale fermentations. The accuracy of quantification of volatile acidity in both Chenin blanc and synthetic must was excellent, and the standard error of prediction was 0.07 g l(-1) and 0.08 g l(-1), respectively. The respective standard error of prediction in Chenin blanc and synthetic musts for ethanol was 0.32% v/v and 0.31% v/v, for glycerol was 0.38 g l(-1) and 0.32 g l(-1), for reducing sugar in Chenin blanc must was 0.56 g l(-1) and for glucose in synthetic must was 0.39 g l(-1). These values were in agreement with the accuracy obtained by the respective reference methods used for the quantification of the components. The screening method was applied to quantify the fermentation products of glycerol-overproducing hybrid yeasts and commercial wine yeasts. Principal component factor analysis of the fermentation data facilitated an overall comparison of the fermentation profiles (in terms of the components tested) of the strains. The potential of Fourier transform infrared spectroscopy as a tool to rapidly screen the fermentative properties of wine yeasts and to speed up the evaluation processes in the initial stages of yeast strain development programs is shown.

Ethanol↗
PubMedDate not supplied

Antimutagenic effects of doenjang (Korean fermented soypaste) and its active compounds.

Doenjang (Korean fermented soypaste) is one of the important fermented foods of Korea. Doenjang has been traditionally manufactured from meju, which is fermented rectangular shape molded from crushed cooked soybeans. The main microorganisms involved for meju fermentation are Bacillus subtilis and molds such as Rizopus sp., Mucor sp., and Aspergillus sp. We have already reported that doenjang is safe from mycotoxin, especially, aflatoxin contamination due to the manufacturing process of the doenjang. We have demonstrated that the doenjang extracts showed strong antimutagenic activities against various carcinogens/mutagens including aflatoxin B(1). The traditionally fermented soypaste, doenjang showed higher antimutagenic activity than the raw soybeans, cooked soybeans, meju and other fermented soybeans in the Ames test. The active compounds that were identified are genistein, linoleic acid, beta-sitosterol glucoside, soyasaponin, etc. The active compounds exhibited strong antimutagenic activities in the Ames test, SOS chromotest and Drosophila wing spot test. More genistein was formed during the doenjang fermentation from genistin in the soybeans. Genistein and linoleic acid were the most effective active compounds found in doenjang.

4-Nitroquinoline-1-oxide↗
PubMed2002

An overview of small-scale food fermentation technologies in developing countries with special reference to Thailand: scope for their improvement.

Small-scale food fermentation technologies in developing countries have evolved through years of experience rather than through scientific breakthroughs. Many small-scale manufacturers are, therefore, reluctant to accept change and modify fermentation processes. Upgrading the quality and safety of fermented foods, while reducing their production cost and maintaining their authenticity and uniqueness, is of utmost importance. One strategic approach, which has been successfully implemented for the improvement of small-scale soy sauce fermentation in Thailand, is the consortium approach. This approach has allowed industry to work closely in sharing knowledge and common problems, which in turn has provided scientists with the research direction that would best benefit the industry. This consortium approach has brought about changes in the methodologies used in the production of soy sauce, by shortening processing times, introducing fiberglass tanks as bioreactors instead of the traditionally used small earthenware containers and introducing cost-effective waste management systems. One barrier to the application of starter cultures in the small-scale fermentation industry is the loss of uniqueness of fermented products. However, the advent of molecular biology techniques has allowed science to tailor starter cultures to the specific requirements of the manufacturer. Using the techniques of molecular biology, it has been shown that microflora of a specific product vary according to origin and sensory quality. A cell bank is being developed to serve as a resource base for Thai fermented pork sausage in order to facilitate the application of starter cultures in the manufacture of that product.

Developing Countries↗
PubMed1999

Saccharomyces cerevisiae cell fatty acid composition and release during fermentation without aeration and in absence of exogenous lipids.

Medium-chain fatty-acids (MCFA) are among the main aroma compounds of fermented beverages. High concentrations of MCFA have been found in sluggish and stuck fermentations. It has been suggested that they arrest cell growth, as they may be toxic, but the causes of sluggish and stuck fermentations are still unclear. The aim of this work was to see whether the production of MCFA is related to fatty acid synthesis in the absence of exogenous lipids and aeration, and whether their increase can be regarded as a consequence, instead of the cause, of sluggish and stuck fermentations. Two possibilities were considered: (i) MCFA are produced to replace unsaturated fatty acids (UFA) for cell membrane fluidity when the lack of oxygen makes desaturation of saturated fatty acids (SFA) impossible; or (ii) MCFA are produced following the release of medium-chain acyl-CoA from the fatty acid synthetase complex (FAS) due to the accumulation of SFA, and their hydrolysis to recycle CoA-SH. In the first hypothesis, MCFA should be active in cell metabolism and be found in cell structures; in the second, MCFA should be a discard and prevalently found outside the cell. We carried out a Saccharomyces cerevisiae fermentation experiment in a synthetic, lipid-free medium without aeration. We measured the fatty acid composition of yeast cells and the amounts of MCFA and their ethyl esters in the medium throughout the fermentation. Cell growth and the oxygen content of the medium were also monitored. We found that MCFA are not immobilized in cell structures, but mainly released into the medium. Cell growth is arrested because fatty acid biosynthesis is prevented by the lack of oxygen. The higher MCFA concentrations found in sluggish and stuck fermentations can be thus regarded as an effect, and not the cause, of this arrest. Some suggestions for the prevention of these events are proposed.

Caproates↗
PubMed2004

Production of heterologous protein by Methylobacterium extorquens in high cell density fermentation.

The green fluorescent protein (GFP) was used as a model protein to study the recombinant protein production by the strain Methylobacterium extorquens ATCC 55366. Scale-up from shake flasks to 20 l fed-batch fermentation was achieved using methanol as a sole carbon and energy source and a completely minimal culture medium. Two different expression vectors were used to express GFP. Clone PCM-GFP containing the vector pCM110 with native promoter of the methanol dehydrogenase PmxaF produced approximately 100-fold more GFP than the clone PRK-GFP containing the vector pRK310 with the heterogeneous promoter Plac. Several fed-batch fermentations with and without selective pressure (tetracycline) were run in a 20 l stirred tank fermenter using the two different clones of M. extorquens. The methanol concentration was monitored with an on-line semiconductor gas sensor in the culture broth. It was maintained at a non-toxic level of 1.4 g l(-1) with an adaptative control which regulates the methanol feed rate. The same growth profile was achieved in all fermentations. The maximum growth rate (micro(max)) was 0.18 h(-1) with an overall yield (Y(X/S)) of 0.3 g g(-1) methanol. With this high cell density fermentation process, we obtained high levels (up to 4 g l(-1)) of GFP with the clone PCM-GFP. The maximum specific GFP production (Y(GFP/X)) with this clone was 80 mg g(-1) representing approximately 16% of the total cell protein. Additional feeding of pure oxygen to the fermenter permitted a longer phase of exponential growth but had no effect on the total yields of biomass and GFP. The specific GFP production of clone PCM-GFP remained unaffected in the presence or absence of selective pressure (tetracycline), within the initial 50 h of the fermentation culture. These results suggest that M. extorquens ATCC 55366 could be an interesting candidate for overexpression of recombinant proteins.

Bacterial Proteins↗
PubMed2000

Influence of fiber fermentability on nutrient digestion in the dog.

Eight mature dogs (17.2 +/- 0.2 kg) surgically fitted with ileal T-cannulas were used in a replicated 4-x-4 Latin-square-design experiment to evaluate nutrient disappearance at the terminal ileum and through the digestive tract. Two fiber types, cellulose, a crystalline, slowly fermented fiber, and pectin, a soluble, rapidly fermented fiber, were fed in different increments, and the effects on nutrient availability were assessed. Treatments included 1) 100% cellulose, 2) 66% cellulose and 33% pectin, 3) 66% pectin and 33% cellulose, and 4) 100% pectin. Fiber was added at 10% of diet dry matter (DM). Diets were fed at 100% of ME for maintenance and offered at 0730 and 1730 h. All periods were 21 d, which included 3 d of diet transition and 7 d of adaptation. Daily DM intake was 210 +/- 5 g. Total tract and large-intestine DM digestibility increased linearly (P < 0.01) with increased pectin. These changes in DM digestion were largely the result of changes in fiber digestion. Fermentation of total dietary fiber in the large intestine went from less than zero to 39% of ileal flow (linear, P < 0.01). Total-tract crude-protein digestibility decreased linearly (P < 0.01) with increased pectin. This study demonstrated that fiber fermentability significantly affects digestion in the dog. Increasing fermentable fiber increased the digestion of DM and energy. However, increased fiber fermentability inversely affects crude protein digestibility. The lower crude-protein digestibility could be attributed to larger microbial protein excretion as a result of greater fermentation of pectin versus cellulose.

Ammonia↗
PubMed2000

Effects of animal or plant protein diets on cecal fermentation in guinea pigs (Cavia porcellus), rats (Rattus norvegicus) and chicks (Gallus gallus domesticus).

Monogastric herbivores such as the guinea pig depend on energy supply from enteric fermentation as short-chain fatty acids (SCFA) corresponding to 30-40% of their maintenance energy requirements. They evolved specific digestive system to adapt their indigenous microflora to plant polysaccharides fermentation. No information has been available about the adaptability of microbial fermentation in hindgut of the monogastric herbivorous to an animal protein diet. We investigated if the guinea pig can fully retrieve energy of an animal protein diet by hindgut fermentation compared with a plant protein diet. For comparison, we also studied two omnivores. End products of in vitro cecal fermentation (SCFA, ammonia and gases) were measured to judge how well an animal protein diet could be fermented. The animal protein diet resulted in the less intensive fermentation with increased feed intake and volume of cecal contents than the plant protein diet only in guinea pigs. This may be due to a limited capacity of the hindgut microflora to adapt to the substrate rich in animal protein. We also found that chick cecal contents produced methane at higher emission rate than ruminants.

Animals↗
PubMed2002

Evolution of carbohydrate fraction in carbonated fermented milks as affected by beta-galactosidase activity of starter strains.

The influence of carbonation on the evolution of lactose, galactose and glucose in fermented milks with added probiotic bacteria (Lactobacillus casei, Lactobacillus acidophilus and/or Bifidobacterium bifidum) was evaluated and related to beta-galactosidase activity of starter strains. During incubation and first days of refrigeration, lactose hydrolysis resulting in the liberation of galactose and glucose occurred in CT (Streptococcus thermophilus/Lb. casei), AT (Str. thermophilus/Lb. acidophilus) and ABT fermented milks (Str. thermophilus/Lb. acidophilus/Bifid. bifidum). Levels of galactose were higher than those of glucose and could be related to the preferential consumption of glucose by actively growing bacteria. Through the incubation, lactose and monosaccharide levels were not affected by milk carbonation. However, during refrigerated storage the presence of this gas was associated with slightly lower content of lactose and higher levels of galactose and glucose in AT and ABT products but not in CT fermented milks. Through the refrigeration galactose was moderately utilised by Lb. acidophilus in AT products whereas the presence of Bifid. bifidum seems to prevent the consumption of this sugar in ABT fermented milks. Glucose remained constant, with minor variations in CT products but a continuous increase of this sugar occurred in carbonated AT and ABT fermented milks during storage. Beta-galactosidase activity displayed by Str. thermophilus strains was similar at pH 6.5 (initial pH of non-carbonated samples) and pH 6.3 (initial pH of carbonated samples) whereas Lb. acidophilus LaA3 showed greater beta-galactosidase activity at pH 6.3 than at higher pH values. Thus, the enhanced metabolic activity of Lb. acidophilus caused by the low initial pH of carbonated milk also promoted higher cellular beta-galactosidase activity that could have released greater amounts of galactose and glucose from lactose in AT and ABT fermented milks through the refrigerated period. In CT fermented milks, similar beta-galactosidase activity levels of Str. thermophilus at pH 6.5 and 6.3 together with the absence of beta-galactosidase activity in Lb. casei could explain the lack of differences on glucose and galactose content between carbonated and non-carbonated samples.

Animals↗
PubMedDate not supplied

Simultaneous saccharification and co-fermentation of crystalline cellulose and sugar cane bagasse hemicellulose hydrolysate to lactate by a thermotolerant acidophilic Bacillus sp.

Polylactides produced from renewable feedstocks, such as corn starch, are being developed as alternatives to plastics derived from petroleum. In addition to corn, other less expensive biomass resources can be readily converted to component sugars (glucose, xylose, etc.) by enzyme and/or chemical treatment for fermentation to optically pure lactic acid to reduce the cost of lactic acid. Lactic acid bacteria used by the industry lack the ability to ferment pentoses (hemicellulose-derived xylose and arabinose), and their growth and fermentation optima also differ from the optimal conditions for the activity of fungal cellulases required for depolymerization of cellulose. To reduce the overall cost of simultaneous saccharification and fermentation (SSF) of cellulose, we have isolated bacterial biocatalysts that can grow and ferment all sugars in the biomass at conditions that are also optimal for fungal cellulases. SSF of Solka Floc cellulose by one such isolate, Bacillus sp. strain 36D1, yielded l(+)-lactic acid at an optical purity higher than 95% with cellulase (Spezyme CE; Genencor International) added at about 10 FPU/g cellulose, with a product yield of about 90% of the expected maximum. Volumetric productivity of SSF to lactic acid was optimal between culture pH values of 4.5 and 5.5 at 50 degrees C. At a constant pH of 5.0, volumetric productivity of lactic acid was maximal at 55 degrees C. Strain 36D1 also co-fermented cellulose-derived glucose and sugar cane bagasse hemicellulose-derived xylose simultaneously (SSCF). In a batch SSCF of 40% acid-treated hemicellulose hydrolysate (over-limed) and 20 g/L Solka Floc cellulose, strain 36D1 produced about 35 g/L lactic acid in about 144 h with 15 FPU of Spezyme CE/g cellulose. The maximum volumetric productivity of lactic acid in this SSCF was 6.7 mmol/L (h). Cellulose-derived lactic acid contributed to about 30% of this total lactic acid. These results show that Bacillus sp. strain 36D1 is well-suited for simultaneous saccharification and co-fermentation of all of the biomass-derived sugars to lactic acid.

Bacillus↗
PubMedDate not supplied

Extractive fermentation for enhanced propionic acid production from lactose by Propionibacterium acidipropionici.

An extractive fermentation process using an amine extractant and a hollow-fiber membrane extractor to selectively remove propionic acid from the fermentation broth was developed to produce propionate from lactose. Compared to the conventional batch fermentation, the extractive fermentation had a much higher productivity ( approximately 1 g/(L.h) or 5-fold increase), higher propionate yield (up to 0.66 g/g or more than 20% increase), higher final product concentration (75 g/L or higher), and higher product purity ( approximately 90%). Meanwhile, acetate and succinate productions in the extractive fermentation were significantly reduced. The improved fermentation performance can be attributed to the reduced product inhibition and a possible metabolic pathway shift to favor more propionic but less acetic and succinic acid production. The process was stable and gave consistent long-term performance over the 1. 5-month period studied. The effects of propionate concentration, pH, and amine content in the solvent on the extractive fermentation were also studied and are discussed in this paper.

Fermentation↗
PubMedDate not supplied

Fermentations with new recombinant organisms.

United States fuel ethanol production in 1998 exceeded the record production of 1.4 billion gallons set in 1995. Most of this ethanol was produced from over 550 million bushels of corn. Expanding fuel ethanol production will require developing lower-cost feedstocks, and only lignocellulosic feedstocks are available in sufficient quantities to substitute for corn starch. Major technical hurdles to converting lignocellulose to ethanol include the lack of low-cost efficient enzymes for saccharification of biomass to fermentable sugars and the development of microorganisms for the fermentation of these mixed sugars. To date, the most successful research approaches to develop novel biocatalysts that will efficiently ferment mixed sugar syrups include isolation of novel yeasts that ferment xylose, genetic engineering of Escherichia coli and other gram negative bacteria for ethanol production, and genetic engineering of Saccharoymces cerevisiae and Zymomonas mobilis for pentose utilization. We have evaluated the fermentation of corn fiber hydrolyzates by the various strains developed. E. coli K011, E. coli SL40, E. coli FBR3, Zymomonas CP4 (pZB5), and Saccharomyces 1400 (pLNH32) fermented corn fiber hydrolyzates to ethanol in the range of 21-34 g/L with yields ranging from 0.41 to 0.50 g of ethanol per gram of sugar consumed. Progress with new recombinant microorganisms has been rapid and will continue with the eventual development of organisms suitable for commercial ethanol production. Each research approach holds considerable promise, with the possibility existing that different "industrially hardened" strains may find separate applications in the fermentation of specific feedstocks.

Escherichia coli↗
PubMed2002

Fermentation of cottonseed and other feedstuffs in cattle rumen fluid.

Bovine rumen fluid was fermented anaerobically over 48 h with cottonseed, corn, alfalfa, or a mixture of these substrates in anaerobic mineral buffer. Samples taken at different incubation times were derivatized with n-butanol and subjected to gas chromatography and mass spectroscopy. No unusual fermentation end-products from the cottonseed substrate were detected. Cottonseed supported rumen fermentation at levels comparable to those of the other substrates. Major components were usually found in the decreasing order of acetate, propionate, butyrate, and valerate, although acetate and propionate concentrations decreased late in the alfalfa and mixed-feed fermentations, eventually allowing butyrate concentrations to exceed those of propionate. As expected, lactate was produced in high concentrations when corn was fermented. The minor components 2-methylpropionate, 2- and 3-methylbutyrate, phenylacetate, phenylpropionate, and caproate also accumulated, with their relative concentrations varying with the substrate. Succinate was produced in substantial amounts only when corn and alfalfa were fermented; it did not accumulate when cottonseed was the substrate. Samples containing cottonseed were derivatized and subjected to reversed-phase high-performance liquid chromatography, revealing that gossypol concentrations did not change during fermentation.

Acetates↗