Fermentacion microbiana

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  • Publicado : 18 de marzo de 2010
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Objectives
The overall objective of this experiment is to produce bioethanol by glucose fermentation with three different strains of Saccharomyces to compare which strain produces more ethanol.
Specifically the laboratory experience aimed to:
• Understand the concepts that involve bioethanol production.
• Carry out a fermentation to develop techniques using the Bioflo 3000bioreactor.
• Prepare yeast growth medium.
• Learn how to inoculate and take samples aseptically from the bioreactor.
• Measure cell growth and draw a growth curve graph using data from the spectrophotometer.
• Use High Performance Liquid chromatography as an analytical tool to determine ethanol concentration at different stages of the fermentation.
• Improve teamwork.

Background

Bioethanol: ethanol as a fuel
The effort to develop bioethanol technology gained significant momentum in the late 1970s as a result of the energy crises that occurred in that decade (6). Today, with rising prices for crude oil and increasing political instability in oil producing countries, the use of bio-based alcohols as solvents or basic chemicals is again underconsideration (1). Total world carbon dioxide emissions from the consumption of fuels increased by 11.4 percent from 1992 to 2001. The largest single portion of the energy used in the US is petroleum-derived fuel, which makes up for more than half of the imported energy (U.S. department of energy, 1995). An accelerated release of fossil entombed CO2 due to human activity is now generally accepted as a majorfactor contributing to the green house effect (1). The Stern-Review on the Economics of Climate Change has publicized the economic necessity to limit global warming. In the last years due to rising environmental concerns and to the periodic crises in some of the larger oil exporting countries, bioethanol has become a viable and realistic alternative in the energy market. Therefore, the developmentof cost-effective technologies for fuel ethanol production is a priority for many research centers, universities and private firms, and even for different governments.
One fuel that has the potential to match the convenient features of petroleum at a relatively low price is ethanol produced from biomass resources (bioethanol). It is already an important element of transportation fuelproduction; about 12% of the gasoline currently sold in the U.S. contains 8% to 10% ethanol as a fuel additive. When added as an additive, bioethanol increases octane and provides oxygen to promote more complete combustion and reduce exhaust emissions of carbon monoxide, unburned hydrocarbons and other toxics. Common gasoline produced, has a petroleum-derived additive that is cause of water pollutionconcerns. Reacting ethanol with isobutylene it forms ethyl tertiary butyl ether (ETBE), an emerging fuel additive that provides the same benefits when added to gasoline as direct alcohol while simultaneously reducing the vapor pressure of the mixture and the evaporative release of fuel compounds that contribute to ozone formation and smog (1). Because ethanol can directly replace this component,ethanol can also be used as an alternative fuel (typically in an 85% blend) to reduce the dependence of foreign oil (which currently supplies more than half the U.S. petroleum demand). Making ethanol from the starch in corn grain already supports a two billion dollar per year industry in the U.S. alone (1).
Like modern crude oil refinery, the bioindustry for biofuels has a dual purpose in the economy,as it is used as a supply of energy as well as basic chemicals. The upcoming “biorefinery” revitalizes the old tradition of a careful thrifty economy and intends to make use of all energy and carbon stored in biomass, feeding by-products into secondary conversion process or refining them as fuel (1).

Technology
Bioethanol can be produced from raw materials containing fermentable sugars as:...
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