Yeast industrial production

The aim is to produce biomass or a mass of cells such as microbes, yeast and fungi. The commercial production of biomass has been seen in the production of baker s yeast, which is used in the baking industry. Production of single cell protein (SCP) is used as biomass enriched in protein.6 An algae called Spirulina has been used for animal food in some countries. SCP is used as a food source from renewable sources such as whey, cellulose, starch, molasses and a wide range of plant waste. 

This intractable problem may now be close to being solved. A Saccharomyces species that expressed the xylose isomerase gene from an anaerobic fungus was found to grow slowly on pentoses [29]. Improvement resulted from a combination of rational engineering - overexpression of the pentose phosphate-converting enzymes (see Fig. 8.5) - and classical strain improvement [30]. The authors conclude The kinetics of xylose fermentation are no longer a bottleneck in the industrial production of ethanol with yeast ... 

Krebs cycle and the constituents of respiratory chains are repressed (Gancedo 1992 Polakis et al. 1965 Barnett and Entian 2005). Therefore, under wine fermentation conditions, Saccharomyces cerevisiae can only ferment sugars. Saccharomyces cerevisiae can only use respiration when the sugar concentration is really low and when oxygen is present in the medium. These conditions are used for the industrial production of selected dry yeast. 

In 1929 Kinoshita [107] identified itaconic acid as the major metaboHc product of A. itaconicus. Later research showed that A. terreus is a better biocatalyst for itaconic acid accumulation. A number of yeast strains belonging to Candida and Rhodotorula [108] can also accumulate a limited amount of itaconic acid. Patents on the industrial production of itaconic acid using Aspergilli as the biocatalyst from molasses were issued in 1961. The currently preferred industrial process uses improved strains of A. terreus as the biocatalyst. The most often studied itaconic acid producers are A. terreus NRRL 265 and A. terreus NRRL 1960. 

S. cerevisiae laboratory strains have been selected for unicellular growth and multiple genetic markers, mainly auxotrophies, to enable easy selection. It has become evident recently that auxotrophic markers impair specific growth rate, chronological hfespan [28], and tolerance to high ethanol concentrations [29]. Therefore, it appears advisable to use wild-type strains for industrial production rather than (auxotrophic) laboratory strains. For many other yeast species, this is less of a concern as most of their laboratory strains are nearly wild type. 

Fermentation a form of metabolism producing incompletely oxidized end products. Per unit of substrate, F. yields far less energy than respiration, e.g. a yeast cell obtains 2 molecules ATP per molecule of glucose when it ferments glucose to ethanol, whereas complete respiration would yield 38 molecules of ATP (see Alcoholic fermentation). Strictly speaking, F. is an anaerobic process (Pasteur defined F. as life without air ) but the term is also widely and loosely applied to certain aerobic processes, such as acetic acid F., and to any industrial production process employing microorganisms in a fermentor (see Fermentation techniques). 

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