Bioreactor large-scale industrial fermentations

Large-Scale Industrial Fermentations Challenges for Bioreactor Modeling... 

The growth of cells on a large scale is called industrial fermentation. Industrial fermentation is normally performed in a bioreactor, which controls aeration, pH and temperature. Microorganisms utilise an organic source and produce primary metabolites such as ethanol,... 

Temperature Ihe temperature in a bioreactor is an important parameter in any bioprocess, because all microorganisms and enzymes have an optimal temperature at which they function most efficiently. For example, optimal temperature for cell growth is 37 °C for Escherichia coli and 30 °C for Saccharomyces sp, respectively. Although there are many types of devices for temperature measurements, metal-resistance thermometers or thermistor thermometers are used most often for bioprocess instrumentation. The data of temperature is sufficiently reliable and mainly used for the temperature control of bioreactors and for the estimation of the heat generation in a large-scale aerobic fermentor such as in yeast production or in industrial beer fermentation. 

Stirred-tank bioreactors are widely used in the modern biotechnological industry. Most products produced from animal cells on a large scale worldwide are manufactured in this type of bioreactor. In general, these reactors are very similar to fermenters used in industrial submerged culture of microorganisms, and are simple to design, having the shape of a tank and impellers to promote mixture of the contents. 

In this example airlift bioreactors were used as it was generally assumed that plant cells are difficult to grow in stirred fermentors, due to their sensitivity for shear forces. However recent studies in our laboratories have shown that this is not a general characteristic of plant cells. Efforts to measure the shear sensitivity of Catharanthus roseus cell cultures were not succesful, as even at stirrer speeds as high as 1000 rpm (normal speed 100 rpm) in a 3 1 vessel, the cells were still viable after one month. Similar results were found for tobacco cell cultures (6). This means that stirred fermentors can also be considered for large scale culture, which makes the economy more favourable, as such fermentors do already exist in fermentation industry, whereas airlift bioreactors are scarcely used. 

This section will review recent reports of attempts to produce PHA. Emphasis will be put on processes using R. eutropha or A. latus, and the survey will be limited to literature on PHA production in bioreactor only. While flask experiments are the necessary first stages in the development of new production strategies (e.g., the use of inexpensive substrates and sources of growth factors, as recently reported in [229] and [230], respectively) and therefore of high interest, the potential of a novel system can be truly assessed only once it has been scaled up to fermentor operation, in which culture conditions at least approach those of industrial fermentations. The other area of research with a possible future impact on large-scale production of PHAs, the use of transgenic plants, will be briefly discussed. 

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