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

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Abstract

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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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.
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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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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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