Evaluación de levaduras nativas productoras de etanol presentes en el bagazo de caña de azúcar

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La hidrólisis química o enzimática del bagazo de caña de azúcar permite la obtención de azúcares fermentables, utilizados en la producción biotecnológica de etanol, mediante el empleo de levaduras comerciales o autóctonas obtenidas de diferentes materiales lignocelulósicos. El objetivo de este trabajo fue valorar la capacidad de producción de etanol de cepas de levaduras nativas, aisladas en medio YPD e hidrolizado de bagazo de caña de azúcar, concentrado hasta un 75 %. Utilizando como variables de estudio el tipo de cepa y el tiempo de proceso, se realizó un análisis multifactorial (ANOVA) para su evaluación. Los resultados obtenidos con la cepa seleccionada UAT-3, fueron para YP/S de 0.441 7 g/g y QP de 0.076 7 g/L·h a las 120 h. Las condiciones de proceso utilizadas en el presente estudio permitieron aislar y seleccionar cepas nativas de Sacharomyces cereviseae, con características adecuadas para ser utilizadas en procesos biotecnológicos industriales de producción de etanol, utilizando como sustrato residuos o subproductos derivados de la industria azucarera como el bagazo de caña de azúcar.

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... Also, it should be noted that ethanol is a net energy source, easily storable, with a high oxygen content (35%) and clean combustion; it is considered to have an excellent potential for application as fuel [12]. Furthermore, a renewable resource is biomass generated by photosynthetic organisms (autotrophs), which store energy in the form of sugars that can be transformed into ethanol through fermentation [13]. ...
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El mucílago es un componente de la vaina de cacao, está constituido por el mesocarpio del fruto y representa el 15-20% del peso del grano fresco, el alto contenido de azúcares reductores que se encuentra en el mucílago de las variedades CCN-51 7.42% de azúcares y 11.36% en Nacional) permitió que el mucílago se degradara fácilmente y de esta manera obtener bioetanol el mismo que fue sometido a diferentes análisis para determinar las características fisicoquímicas, los análisis realizados sobre la degradación del mucílago del cacao CCN51 fueron: pH 4.07, 12.9 Sólidos totales, 0.9% acidez total, 60 °GL, turbidez de 2.93 NTU, una densidad de 0.91 g / cm3, y calor específico de 0.92 kJ / Kg ° C, mientras que la variedad Nacional obtuvo un pH de 4.67, 13.6 de sólidos totales, 1.7 g / cm3 de acidez total, 52 °GL, turbidez 9,33 NTU, una densidad de 0,93 g/cm3 y calor específico de 0,95 kJ/Kg °C. La concentración de levadura Saccharomyces cerevisiae aplicada para obtener bioetanol y que mejores resultados se obtuvieron es del 0,05% esto permite que durante el proceso de fermentación del bioetanol a partir del mucílago del cacao los azúcares se oxiden más fácilmente para producir un mayor contenido alcohólico.
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Bio-Ethanol is a renewable; eco-friendly energy source can be produced from bio-mass (hemicelluloses). Pteris (fern) is grown very fast and has not major economic importance but it is a reliable source of hemicelluloses can be converted to bio-Ethanol. In the hydrolysis of hemicelluloses the concentration of glucose and the reaction rate was observed with respect to the different parameters, like pH, temperature, substrate diameter, substrate loading. In this study we found optimal parameters, NH 4 OH treatment as the best treatment among H 2 SO 4, NH 4 OH, and NaOH treatment. In addition, pH 7, temperature 35°C, substrate diameter 45μm-63μm, and substrate loading 0.25gm in 100ml working volume was found as optimum operation condition for hydrolysis reaction, which was carried out by pseudomonas sp., isolated from cow dung. In this experiment sugar concentration was measured with UV spectrophotometer using DNS reagent finding the equilibrium time is 72hours for hydrolysis process and the maximum sugar concentration of 1.7625mg/l was achieved. Subsequently we study the fermentation process using yeast to produce Bio-Ethanol from reducing sugar solution obtained from the hydrolysis process on optimum reaction condition and yield the Ethanol concentration 0.333 mg/L, measured with UV spectrophotometer. Furthermore, it was also observed that the activity of yeast was sustain, in the reaction condition (pH = 7, temperature = 25°C), only for 50 hours. In sum, it could be conclude that 0.1332 mg of ethanol can be produce from 1gm of pteris where the conversion of reducing sugar to ethanol is 20% approximately in the optimum reaction condition., "Production of Bio-fuel (Bio-Ethanol) from Biomass (Pteris) by Fermentation Process with Yeast." Sustainable Energy, vol. 2, no. 1 (2014): 25-28. doi: 10.12691/rse-2-1-5.
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Bioconversion of hemicellulosic sugars into second generation (2G) ethanol plays a pivotal role in the overall success of biorefineries. In this study, ethanol production performance of a novel xylose-fermenting yeast, Scheffersomyces shehatae UFMG-HM 52.2, was evaluated under batch fermentation conditions using sugarcane bagasse (SB) hemicellulosic hydrolysate as carbon source. Dilute acid hydrolysis of SB was performed to obtain sugarcane bagasse hemicellulosic hydrolysate (SBHH). It was concentrated, detoxified, and supplemented with nutrients in different formulations to prepare the fermentation medium to the yeast evaluation performance. S. shehatae UFMG-HM 52.2 (isolated from Brazilian Atlantic rain forest ecosystem) was used in fermentations carried out in Erlenmeyer flasks maintained in a rotator shaker at 30 ∘ C and 200 rpm for 72 h. The use of a fermentation medium composed of SBHH supplemented with 5 g/L ammonium sulfate, 3 g/L yeast extract, and 3 g/L malt extract resulted in 0.38 g/g of ethanol yield and 0.19 g L.h of volumetric productivity after 48 h of incubation time.
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Sugarcane bagasse is now a major source of fibre for pulp and papermaking in Mexico, bagasse pulps are used for all grades of paper: writing, toilet tissue, towelling, glassine, and others. The storage and handling of fibres are critical factors in the resulting pulp yield and quality because bagasse is a fibrous residue that remains after crushing the stalks, and contains short fibres and is a seasonal raw material. The storage produced at harvest time becomes necessary when it is used for operations that are carried out continuously throughout the year, such as pulp and paper production. Nevertheless the sugar cane bagasse fibers suffer severe degradation while in storage due to the action of undesirable microorganisms. The causes for the deterioration as fermentation proceed and the methods of storing and handling the bagasse to minimize this degradation are discussed. The purpose of this paper is to analyze the impact of quality from bagasse stored for 12 months on mechanical pulp properties compared with those of corresponding bleached and unbleached pulp made from mills bagasse (fresh bagasse). Soda pulping from storaged bagasse gave the best results in yield, degree of delignification and brightness; but it was found that all of the pulp strength and drainage properties were increased to the fresh bagasse pulp (burst index 42%, folding endurance 610% and breaking length 53%, Freeness 10%, drainage time of pulp 4.2%, porosity 20% and refinement degree 17.6%) however, tear index was reduced 14.2%. The analysis showed the influence of storage method on the mechanical properties of bleached and unbleached bagasse pulp and the need for an improved wet bulk storage system to produce acceptable quality chemical bagasse pulps from conventional bleaching method (CEH sequence) and ECF y TCF pulps.
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The ethanol yield and productivity obtained during fermentation of lignocellulosic hydrolysates is decreased due to the presence of inhibiting compounds, such as weak acids, furans and phenolic compounds formed or released during hydrolysis. This review describes the effect of various detoxification methods on the fermentability and chemical composition of the hydrolysates. Inhibition of fermentation can be relieved upon treatment with the ligninolytic enzyme laccase, pre-fermentation by the filamentous fungus Trichoderma reesei, removal of non-volatile compounds, extraction with ether or ethyl acetate, and treatment with alkali or sulfite. Various fermentation strategies can also be used to improve yield and productivity in lignocellulosic hydrolysates. Batch, fed-batch, and continuous fermentation are discussed in relation to inhibition of fermentation in lignocellulosic hydrolysates.
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The viability of the Mexican sugar industry is a political imperative. Sugar is Mexico’s largest agricultural industry. Sugar cane is the first largest cultivated crop, supplying raw material to over 57 mills located in 15 states. The current inefficiency of the Mexican industry and the advent of increased production, displacing domestic sugar used in soft drinks; and the government issued a large number of import permits thus allowing large quantities of lower price world sugar like HFCS to enter the domestic market. All together these factors contributed to crisis of sector. The industry should be restructured and downsized to be competitive producing ethanol (EtOH), like the easiest ways to increase the predominate alternate fuel and the opportunity to make the Mexican sugar cane future a reality. If the ethanol (EtOH) is produced, it’s possible to see a growing role for renewables in the Mexican’s energy future, the factories sugar must involve them as partners in the continued expansion of ethanol production and use in México, export opportunities, increase public awareness of ethanol’s benefits and create an economic climate for ethanol’s expanded use. The flexibility of production of sugar and ethanol at the factories will allow a role for ethanol to be used to achieve the nation’s clean air goals. The most important opportunity for sugar cane industry is to continue to reduce ethanol production costs through genetic engineering, feedstock diversity using whole sugar cane and technology improvements.
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Hemicelluloses, the second most abundant polysaccharide in nature, are well suited for ethanol production due to their enormous availability, low cost and environmental benign process. The major fraction in hemeicelluloses is pentosans and the conversion of pentosans to ethanol is problematic. To get the process economized, the conversion of hemicellulose to ethanol with a satisfactory yield is necessary. In recent years, significant advances have been made towards the technology of pentosans to ethanol conversion. However, there are technical and economical impediments to the development of commercially viable processes utilizing hemicellulosic derived sugars. This article provides an overview of the new insights in pentose sugars conversion into ethanol, pentoses resources, microorganisms and the technology.
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During hydrolysis of lignocellulosic materials a wide range of compounds which are inhibitory to microorganisms are formed or released. Based on their origin the inhibitors are usually divided in three major groups: weak acids, furan derivatives, and phenolic compounds. These compounds limit efficient utilisation of the hydrolysates for ethanol production by fermentation. If the inhibitors are identified and the mechanisms of inhibition elucidated, fermentation can be improved by developing specific detoxification methods, choosing an adapted microorganism, or optimising the fermentation strategy. The present review discusses the generation of inhibitors during degradation of lignocellulosic materials, and the effect of these on fermentation yield and productivity. Inhibiting mechanisms of individual compounds present in the hydrolysates and their interaction effects are reviewed.
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The ethanol production in Colombia represents one of the more important economic lines, produced like antiseptic, reliable alcohol and additive for the gasoline. The porpuse of this work was of to increase the efficiency in the production of ethanol and to find a microorganism that represents an alternative in production, in front a Saccharomyces cerevisiae it. Stocks of Zymomonas mobilisto var. mobilis (Zmm1 and Zmm2) and pomaceae (Zmp1 and Zmp2), they were isolated of samples of molasses of sugar cane in order to previously make a comparative study with results reported from free cells. A stock was used control Zymomonas mobilis mobilis (CETC) 560, considered high ethanol producer. Free cells in fermentador of 1L and were immobilized in matrix of calcium alginate. At the end of the fermentation process the ethanol production was determined by picnometry; results revealed to a concentration of immobilization of 2% p/v, a yield of 92. 1%, on the part of the native stocks Zmm1 and Zmm2 and of 97. 85%, with Zmm compared 560, with the obtained yields of ethanol from free cells, 72. 9% on the part of Zmm1 and 76. 74% with Zmm 560. The analysis of these data, demonstrates to the advantages of the use of immobilized cells forehead to free cells, in fermentation processes, representing a great possibilities for the Biotechnological development of our country, since they allow to consider a Zymomonas mobilis sp . like an alternative for ethanol production on industrial scale, specially the native stocks Zmm1 and Zmm2 that was part of this study. La producción de etanol en Colombia representa uno de los renglones económicos más importantes, producido como alcohol antiséptico, solvente y aditivo para la gasolina. El objetivo de este trabajo fue aumentar la eficiencia en la producción de etanol y encontrar microorganismos que representen una alternativa en producción frente a Saccharomyces cerevisiae . Cepas de Zymomonas mobilis, var. mobilis (Zmm1 y Zmm2) y pomaceae (Zmp1 y Zmp2), fueron aisladas de muestras de melazas de caña con el propósito de realizar un estudio comparativo con resultados reportados anteriormente a partir de células libres. Fue utilizada una cepa control Zymomonas mobilis mobilis (CETC) 560, considerada alta productora de etanol. Células libres en fermentador de 1L y se inmovilizaron en matriz de alginato de calcio. Al final del proceso de fermentación fue determinada la producción de etanol por picnometría. Los resultados revelaron a una concentración de inmovilización del 2% p/v, un rendimiento de 92.1%, por parte de las cepas nativas Zmm1 y Zmm2 y de 97.85%, con Zmm 560, comparado con los rendimientos de etanol obtenidos a partir de células libres, de 72.9% por parte de Zmm1 y 76.74% con Zmm 560. El análisis de estos datos, demuestran las ventajas de la utilización de células inmovilizadas frente a células libres, en procesos de fermentación y representan grandes posibilidades para el desarrollo Biotecnológico de nuestro país, ya que permiten considerar a Zymomonas mobilis sp., como alternativa para producción de etanol a escala industrial, especialmente las cepas autóctonas Zmm1 y Zmm2 que hicieron parte de este estudio.
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La obtención de etanol a partir de biomasa lignocelulósica mediante un proceso de Sacarificación y Fermentación Simultáneas (SFS), requiere un pretratamiento previo de la biomasa que altere su estructura, facilitando la acción de los enzimas. Durante el pretratamiento se forman una serie de productos de degradación que pueden afectar al microorganismo, actuando como potenciales inhibidores de la fermentación. Estos productos (ácidos alifáticos, productos de degradación de azúcares y compuestos aromáticos de degradación de la lignina) no solubilizados y recuperación en la fracción líquida obtenida tras el pretratamiento. En este trabajo se han identificado los productos de degradación generados en el pretratamiento por explosión por vapor de madera de chopo, estudiándose el efecto de estos compuestos sobre la producción de biomasa y etanol de la levadura termotolerante Kluveromyces marxianus, tanto individualmente como en combinaciones binarias y ternarias. Se ha estudiado la influencia del pH del medio de fermentación sobre la toxicidad de los ácidos y la asimilación de estos productos tóxicos por el microorganismo. Finalmente, se ha estudiado el aprovechamiento de la fracción líquida como medio de fermentación para producir etanol a partir de biomasa mediante un proceso de Sacarificación y Fermentación Simultáneas (SFS). El objetivo es reducir la cantidad de agua residual generada en el pretratamiento y disminuir la necesidad de agua en el proceso. Para ello se ha sometido a la fracción líquida generada en el pretratamiento a distintos tratamientos de destoxificación (neutralización, evaporación, procesos de oxidación avanzada y aplicación de zeolitas) con objeto de aumentar su fermentabilidad. La aplicación de un tratamiento de destoxificación, hace posible utilizar esta fracción líquida como medio para producir etanol en un proceso de SFS, permitiendo un ahorro de entre el 30 y 60% del agua utilizada en el proceso
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ResumenAutoctonous yeasts having fermentation ability in producing ethanol from Musa (AAB Simmonds) plantain surplus pulp in the Córdoba department of Colombia Resumen: Se evaluó la capacidad fermentativa de levaduras nativas de la zona costanera del departamento de Córdoba, Colombia, para la obtención de etanol a partir de la pulpa de excedentes de plátano Musa (AAB Simmonds), con el objetivo de encontrar cepas eficientes. Los microorganismos utilizados correspondieron a las especies: Kloeckera sp, Candida guillliermondii 14AD, Candida albicans y Candida guillliermondii 13AD (nativas), y una cepa comercial de referencia, Saccharomyces cerevisiae T73. La fermentación se realizó a diferentes concentraciones de sustrato, siendo la concentración del 40% la mejor; se evaluó la producción de etanol mediante el método colorimétrico del dicromato de potasio utilizando un equipo espectrofotómetro Lambda 11. Se observó que la levadura Candida guilliermondii 14AD nativa fue la más eficiente con una producción promedio de 3,45% v/v de etanol a las 72 horas de fermentación; no se encontraron diferencias estadísticamente significativas con la producción de etanol a partir de la cepa de referencia, la cual produjo 3,59% v/v. Estos resultados sugieren la existencia de levaduras nativas con capacidad para ser utilizadas en la obtención de etanol a partir de material residuo de plátano.Palabras clave: etanol; fermentación; levaduras; método del dicromato de potasio. Abstract: Native yeasts’ (Cordoba, Colombia) fermentation ability for producing ethanol from plantain (Musa AAB Simmonds) surplus pulp was evaluated; the object was to find efficient yeasts. The microorganisms used here came from the Kloeckera sp, Candida guillliermondii (14AD), Candida albicans and Candida guilllier-mondii 13AD strains (native) and Saccharomyces cerevisiae T73 (a commercial reference yeast). Fermentation was carried out on different substrate concentrations, the 40% one giving the best result; ethanol production was evaluated by the potassium dichromate colorimetric method using a Lambda 11 spectrophotometer. It was observed that the Candida guilliermondii 14AD native yeast was the most efficient, having an average 3.45% v/v ethanol production after 72 hours’ fermentation. There were no statistically significant differences compared to reference yeast strain ethanol production (3.59% v/v). These results suggest that native yeasts can be used in obtaining ethanol from residual plantain matter.Key words: ethanol; fermentation; yeast; potassium dichromate method.
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The killer phenomenon in yeasts has been revealed to be a multicentric model for molecular biologists, virologists, phytopathologists, epidemiologists, industrial and medical microbiologists, mycologists, and pharmacologists. The surprisingly widespread occurrence of the killer phenomenon among taxonomically unrelated microorganisms, including prokaryotic and eukaryotic pathogens, has engendered a new interest in its biological significance as well as its theoretical and practical applications. The search for therapeutic opportunities by using yeast killer systems has conceptually opened new avenues for the prevention and control of life-threatening fungal diseases through the idiotypic network that is apparently exploited by the immune system in the course of natural infections. In this review, the biology, ecology, epidemiology, therapeutics, serology, and idiotypy of yeast killer systems are discussed.
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Four strains of bakers' yeast were analysed for their hyperosmotic responses when in media that mimic conditions occurring in bread doughs. Two of the strains produced strong fermentative activity in medium with low osmotic stress, but produced considerably less ethanol in high sucrose concentration medium. Two other strains produced more similar fermentation activities across the range of media tested. The strains that were inhibited by high sucrose concentration were unable to produce significant amounts of glycerol under hyperosmotic conditions. By contrast, the yeasts that were not inhibited significantly by high sucrose produced a considerable amount of glycerol. The strains that produced significant glycerol exhibited efficient expression of the glycerol-3-phosphate dehydrogenase gene GPD1. These novel data on the molecular responses of industrially relevant strains of bakers' yeasts are prerequisite to designing strategies for improving the performance of industrial yeasts in high sugar concentration media.
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Killer yeasts secrete proteinaceous killer toxins lethal to susceptible yeast strains. These toxins have no activity against microorganisms other than yeasts, and the killer strains are insensitive to their own toxins. Killer toxins differ between species or strains, showing diverse characteristics in terms of structural genes, molecular size, mature structure and immunity. The mechanisms of recognizing and killing sensitive cells differ for each toxin. Killer yeasts and their toxins have many potential applications in environmental, medical and industrial biotechnology. They are also suitable to study the mechanisms of protein processing and secretion, and toxin interaction with sensitive cells. This review focuses on the biological diversity of the killer toxins described up to now and their potential biotechnological applications.
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Modification of ethanol productivity and yield, using mineral medium supplemented with glucose or xylose as carbon sources, was studied in ethanologenic Escherichia coli KO11 by increasing the activity of five key carbon metabolism enzymes. KO11 efficiently converted glucose or xylose to ethanol with a yield close to 100% of the theoretical maximum when growing in rich medium. However, when KO11 ferments glucose or xylose in mineral medium, the ethanol yields decreased to only 70 and 60%, respectively. An increase in GALP(Ec) (permease of galactose-glucose-xylose) or PGK(Ec) (phosphoglycerate kinase) activities did not change xylose or glucose and ethanol flux. However, when PDC(Zm) (pyruvate decarboxylase from Zymomonas mobilis) activity was increased 7-fold, the yields of ethanol from glucose or xylose were increased to 85 and 75%, respectively, and organic acid formation rates were reduced. Furthermore, as a response to a reduction in acetate and ATP yield, and a limited PDC(Zm) activity, an increase in PFK(Ec) (phosphofructokinase) or PYK(Bs) (pyruvate kinase from Bacillus stearothermophilus) activity drastically reduced glucose or xylose consumption and ethanol formation flux. This experimental metabolic control analysis showed that ethanol flux in KO11 is negatively controlled by phosphofructokinase and pyruvate kinase, and positively influenced by the PDC(Zm) activity level.
México posee un marco normativo desde 2008 para impulsar la pro­ducción de bioenergéticos, pero está aún no se incrementa en forma significativa; no obstante, existen regiones y estados interesados en ponerse a la vanguardia, como el estado de Veracruz, donde el gobierno estatal promueve la siembra de cultivos destinados a la producción de biocombustibles, así como, la reconversión industrial del aprovechamiento de la caña de azúcar. La región Córdoba-Paso del Macho representa una zona de alto interés porque allí se locali­zan nueve de los 18 ingenios del estado y están establecidas tres empresas que producen bioeta­nol. El propósito de este estudio fue analizar la política estatal en materia de biocombustibles, prin­cipalmente con caña energética, sus alcances socio-económicos y probables externalidades socio-ambientales al incorporarse como regiones productoras. Se realizó un análisis documental, bibliográfico y hemerográfico, de las publicacio­nes realizadas sobre el tema en el periodo de 2009 a 2013. Se visitó ésta región en los meses de julio a agosto de 2011, realizando talleres participativos en tres comunidades, así como 20 entrevistas semi-estructuradas a diversos agentes involucrados en la producción cañera. Los resultados permitieron observar que Veracruz carece de un proyecto energético integral a pesar de sus importantes reservas petrol­eras y que finca su interés en atraerinversiones extranjeras, dificul­tando el tránsito hacia una política energética basada en los recursos renovables y las capacidades locales ambientales, tecnológicas y sociales. Los agrocombustibles represen­tan una alternativa regional, en pequeña y mediana escala para la producción de biocomubustibes, pero deben establecerse mecanis­mos normativos que garanticen el uso diversificado del suelo, para conservar el abastecimiento de ali­mentos y evitar su encarecimiento. Se requiere adicionalmente con­siderar la rentabilidad social y establecer mecanismos estrictos de control para preservar las áreas naturales protegidas. Archivo XML (SciELO)
Biotechnology represents a viable alternative for a sustainable industrial development, as it provides the tools needed to adapt and modify organisms, products systems, and processes to improve industrial activity. This makes it more profitable, diverse and friendly with the environment than the traditional chemical and physical processes. In this regard, extremophilic microorganisms represent the most promising option as a source of biomolecules with biocatalytic capacity, able to withstand drastic process conditions; In addition, their full-scale use may lead to industrials sustainability.
Suitability of 8 different peach cultivars ('Sunhaven', 'Redhaven', 'Kateroo', 'J.H. Hale', 'Flavorcrest', 'July Elberta', 'Stark Early Giant', 'Richahaven') for wine preparation was determined. On the basis of highest diameter, length, pulp content and total sugar; optimum acidity and medium total phenols, the cultivars 'J.H. Hale', 'Sunhaven', 'Redhaven' and 'Kateroo' were rated superior. To prepare wine, the peach pulp was diluted in 1:1 ratio, raising the initial TSS to 24 degrees B, adding pectinol (0.5%), DHAP (0.1%), followed by fermentation with Saccharomyces cerevisiae var. ellipsoideus (5%). The must of cultivars viz. 'Kateroo', 'Sunhaven' and 'Flavorcrest' gave the highest rate of fermentation and ethanol content. With highest phenols (278-306 ppm), total esters (75-101 ppm) and alcohol contents (10.8-11.8% v/v) and lowest volatile acidity (0.020-0.023% A.A.), aldehyde (43-56 ppm) and higher alcohols (113-131 ppm), wines of cultivars 'Redhaven', 'J.H. Hale', 'Sunhaven' and 'Flavorcrest' were found to be superior. Based on the sensory quality, the wines of all the cultivars were acceptable but those of 'Redhaven', 'Sunhaven', 'J.H. Hale', 'Flavorcrest' and 'July Elberta' were adjudged better than others. It is concluded that cultivars 'Redhaven', 'Richahaven', 'J.H. Hale, 'Sunhaven' and 'Flavorcrest' and 'July Elberta' are suitable for preparation of wine.
The influence of the severity of dilute sulfuric acid hydrolysis of spruce (softwood) on sugar yield and on the fermentability of the hydrolysate by Saccharomyces cerevisiae (Baker’s yeast) was investigated. Fermentability was assessed as the ethanol yield on fermentable sugars (mannose and glucose) and the mean volumetric productivity (4 h). The hydrolysis conditions, residence time, temperature, and sulfuric acid concentration were treated as a single parameter, combined severity (CS). When the CS of the hydrolysis conditions increased, the yield of fermentable sugars increased to a maximum between CS 2.0–2.7 for mannose, and 3.0–3.4 for glucose above which it decreased. The decrease in the yield of monosaccharides coincided with the maximum concentrations of furfural and 5-hydroxymethylfurfural (5-HMF). With the further increase in CS, the concentrations of furfural and 5-HMF decreased while the formation of formic acid and levulinic acid increased. The yield of ethanol decreased at approximately CS 3; however, the volumetric productivity decreased at lower CS. The effect of acetic acid, formic acid, levulinic acid, furfural, and 5-HMF on fermentability was assayed in model fermentations. Ethanol yield and volumetric productivity decreased with increasing concentrations of acetic acid, formic acid, and levulinic acid. Furfural and 5-HMF decreased the volumetric productivity but did not influence the final yield of ethanol. The decrease in volumetric productivity was more pronounced when 5-HMF was added to the fermentation, and this compound was depleted at a lower rate than furfural. The inhibition observed in hydrolysates produced in higher CS could not be fully explained by the effect of the by-products furfural, 5-HMF, acetic acid, formic acid, and levulinic acid.
Economic interest in xylitol production can be enhanced if the needed xylose solutions can be obtained from the hydrolysis of low-cost lignocellulosic wastes. Sugar cane bagasse is a renewable, cheap and widely available waste in tropical countries. The hydrolysis of sugar cane bagasse to obtain xylose solutions has a double consequence, the elimination of a waste and the generation of a value-added product. The objective of this work was to study the xylose production from sugar cane bagasse by sulphuric acid hydrolysis at several temperatures (100, 122 and 128 °C) and concentrations of acid (2%, 4% and 6%). Kinetic models were developed to explain the variation with time of xylose, glucose, acetic acid and furfural generated in the hydrolysis. Optimal conditions found were 2% H2SO4 at 122 °C for 24 min, which yielded a solution with 21.6 g xylose/l, 3 g glucose/l, 0.5 g furfural/l and 3.65 g acetic acid/l. In these conditions, ≈90% of the hemicelluloses was hydrolysed.
Enzymatic hydrolysis of pretreated sugarcane bagasse was performed to investigate the production of ethanol. The sugarcane bagasse was pretreated in a process combining steam explosion and alkaline delignification. The lignin content decreased to 83%. Fed-batch enzymatic hydrolyses was initiated with 8% (w/v) solids loading, and 10FPU/g cellulose. Then, 1% solids were fed at 12, 24 or 48h intervals. After 120h, the hydrolysates were fermented with Saccharomyces cerevisiae UFPEDA 1238, and a fourfold increase in ethanol production was reached when fed-batch hydrolysis with a 12-h addition period was used for the steam pretreated and delignified bagasse.
In Mexican alcohol distilleries using sugarcane molasses, one reason for low alcoholic fermentation efficiency is the use of inferior yeast cultures. The objective of the present study was to isolate and select yeast strains from alcoholic fermentations of natural sources (sugarcane molasses, grape juice, cane juice and pineapple) from Veracruz city market and Mexican distilleries, and to evaluate their performance under laboratory conditions in an effort to select superior strains for industrial fermentations. Ethanol production, glucose composition, growth rate, “Killer” activity, ethanol and glucose tolerance of the most promising strains were monitored on synthetic and molasses media. A total of 112 yeast strains were isolated by their capacity to produce ethanol, and from these, only 58 were selected on the basis of best ethanol theoretical yields (88–96%). These strains were exposed several times to high concentrations of glucose and ethanol in order to select ethanol- and glucose-tolerant yeast; 10 were obtained that adapted best to these conditions and that showed “Killer” activity. Of these strains, U3-11, M11, JC10 and U2-10 (obtained from grape juice, sugarcane molasses and cane juice) demonstrated the highest adaptation to both ethanol (5–7% w/v) and glucose (20% w/v). The maximum yield obtained was 0.46 g/g (90% theoretical yield) in a 20-L bioreactor with cane molasses under nonsterile conditions. The selected yeasts could be introduced into industrial processes in Mexican distilleries using sugarcane molasses in order to improve productivity and diminish contamination problems.
Cachaa (aguardente) is a rum-style spirit made from sugar cane juice by artisanal methods in Brazil. A study was made of the production, biochemistry and microbiology of the process in fifteen distilleries in Sul de Minas. Identification of 443 yeasts showed Saccharomyces cerevisiae to be the predominant yeast but Rhodotorula glutinis and Candida maltosa were predominant in three cases. Bacterial infection is a potential problem, particularly in older wooden vats, when the ratio of yeasts:bacteria can be 10:1 or less. A study of daily batch fermentations in one distillery over one season in which 739 yeasts were identified revealed that S. cerevisiae was the predominant yeast. Six other yeast species showed a daily succession: Kluyveromyces marxianus, Pichia heimii and Hanseniaspora uvarum were present only at the beginning, Pichia subpelliculosa and Debaryomyces hansenii were detected from mid to the end of fermentation, and Pichia methanolica appeared briefly after the cessation of fermentation. Despite a steady influx of yeasts from nature, the species population in the fermenter was stable for at least four months suggesting strong physiological and ecological pressure for its maintenance. Cell densities during the fermentation were: yeasts – 4 108/ml; lactic acid bacteria – 4 105/ml; and bacilli – 5 104/ml. Some acetic acid bacteria and enterobacteriaceae appeared at the end. Sucrose was immediately hydrolysed to fructose and glucose. The main fermentation was complete after 12 hours but not all fructose was utilised when harvesting after 24 hours.
Fermentation of d-xylose by Pichia stipitis was inhibited by acetic acid and the degree of inhibition depended on the acetic acid concentration, the availability of oxygen, and the pH. A 50% inhibition of the volumetric rate of ethanol production occurred at acetic acid concentrations of 0.8 and 13.8 g l−1 at pH 5.1 and 6.5, respectively under anaerobic conditions. No acetic acid was utilized in the absence of oxygen. Under oxygen-limited conditions at pH 6.5, an acid hydrolysate of sugar cane bagasse containing (g l−1) d-xylose (40.9), d-glucose (3.1), l-arabinose (4.5), and acetic acid (9.0) was fermented to ethanol at a rate of 0.15 g(l h)−1, and an ethanol yield of 0.27 g g−1 sugar was obtained. When the hydrolysate was treated with an anion exchange resin, 84% of the acetic acid was removed and the subsequent fermentation resulted in a rate of ethanol production [0.56 g(l h)−1] and an ethanol yield (0.37 g g−1 sugar) similar to that obtained in a xylose-arabinose-glucose medium lacking acetic acid.
The great variety of agaves and their multiple uses have played an important role in the cultural identification of Mexico. They have been exploited in many ways for over 10,000 years, and one of these applications is the production of alcoholic nondistilled and distilled beverages. Most of the production processes of these Mexican beverages involve a complex fermentation in which bacteria (mainly lactic and acetic acid) and yeasts (non-Saccharomyces and Saccharomyces) are present in stable mixed populations, or succeeding one another, and have a significant impact on the sensorial characteristics and nutritive value of the final product. This minireview focuses on several nondistilled and distilled Agave beverages, their production area, the Agave species used in their elaboration, the functional microbiota involved in the fermentation process, their fermentation products (when known), the biochemical changes of these unique fermentations, and their impact on the quality and sensorial characteristics of the product.
The effect of acetic acid concentration on xylose-fermentation to xylitol by Candida guilliermondii FTI 20037 was evaluated in semisynthetic medium containing different concentrations of the acid. Increasing acetic acid concentration up to 1.0 g/l favored xylitol yield and productivity, with maximum values of 0.82 g/g and 0.57 g/l.h, respectively. The presence of acetic acid reduced cell production at all concentration. Furthermore, acetic acid was assimilated by the yeast together with the sugars and was depleted from the medium at concentrations of less than 3.0 g/l. The ability of this yeast to assimilate acetic acid suggests that these cells act as agents of medium detoxification. This behavior may lead to a viable microbiological process of xylitol production by C. guilliermondii FTI 20037 using xylose-rich lignocellulosic hydrolysates in which acetic acid is commonly present, causing inhibition of fermentative activity.
Ethanol production was evaluated from wheat straw (WS) hemicellulose acid hydrolysate using an adapted and parent strain of Pichia stipitis. NRRL Y-7124. The treatment by boiling and overliming with Ca(OH)(2) significantly improved the fermentability of the hydrolysate. Ethanol yield (Yp/s) and productivity (Qp av) were increased 2.4+/-0.10 and 5.7+/-0.24 folds, respectively, compared to neutralized hydrolysate. Adaptation of the yeast to the hydrolysate resulted further improvement in yield and productivity. The maximum yield was 0.41+/-0.01 g(p) g(s)(-1), equivalent to 80.4+/-0.55% theoretical conversion efficiency. Acetic acid, furfurals and lignins present in the hydrolysate were inhibitory to microbial growth and ethanol production. The addition of these inhibitory components individually or in various combinations at a concentrations similar to that found in hydrolysate to simulated medium resulted a reduction in ethanol yield (Yp/s) and productivity (Qp av). The hydrolysate used had the following composition (expressed in g x l(-1)): xylose 12.8+/-0.25; glucose 1.7+/-0.3; arabinose 2.6+/-0.21 and acetic acid 2.7+/-0.33.
Owing to technical improvements in the processes used to produce ethanol from biomass, construction of at least two waste-to-ethanol production plants in the United States is expected to start this year. Although there are a number of robust fermentation microorganisms available, initial pretreatment of the biomass and costly cellulase enzymes remain critical targets for process and cost improvements. A highly efficient, very low-acid pretreatment process is approaching pilot testing, while research on cellulases for ethanol production is expanding at both enzyme and organism level.
Ethanol is the major product of yeast sugar fermentation and yet, at certain concentrations, it is very toxic to yeast cells. The major targets for ethanol's toxicity are the plasma membrane and the cytosolic enzymes: ethanol alters membrane organization and permeability and inactivates and unfolds globular cytosolic enzymes. The effects of ethanol on the plasma membrane are attenuated by the presence of trehalose, a disaccharide of glucose that is accumulated simultaneously with urea. The data presented in this paper show that trehalose is not effective at protecting yeast cytosolic inorganic pyrophosphatase against the inactivation of its catalytic activity promoted by alcohols. In contrast, 1 M trehalose increased the toxicity of alcohols against pyrophosphatase by at least 34%. On the other hand, 1.5 M urea attenuated the inactivation of pyrophosphatase promoted by alcohols by approximately 50%. Here we propose that, in the presence of alcohols, urea functions as a molecular filter, enriching the vicinity of the protein with water and excluding alcohol molecules. Conversely, trehalose tends to increase the interaction of alcohols with protein molecules, by withdrawing water, leading to a stronger inactivation promoted for a given concentration of alcohol in the bulk solution on pyrophosphatase activity.
The study of the fermentation performance of Saccharomyces cerevisiae strains under high sugar stress during the vinification of partially dried grapes. Microvinification of partially dried grape must with sugar concentration of 35 degrees Brix was performed using four commercial strains to carry out alcoholic fermentation. A traditional red vinification without nutrients addition was applied. Yeasts displayed different efficiency to convert sugar in ethanol and varied in glycerol yield. Sugar consumption and ethanol level were attested at 80-87% and 143.5-158.0 g l(-1) respectively. High correlation between sugar and assimilable nitrogen consumption rate was observed. Statistical treatment of data by principal component analysis highlighted the different behaviours that strains exhibited in regard to the production of higher alcohols and other compounds important to wine quality. Saccharomyces cerevisiae strains displayed appreciable capability to overcome osmotic stress and to yield ethanol fermenting high sugar concentration grape must in winemaking condition. The results provided insights on the strain contribution to wine quality subordinate to stress condition. This investigation is of applicative interest for winemaking and processing industry that use high sugar concentration musts.
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