1.2 Production and Purification
Generally, large-scale microbial cultivation or cell culture, and product purification steps are carried out in a stepwise manner (Fig. 1-2).
Figure 1-2 Steps in Large Scale Biotechnological Processes
A typical procedure begins with the formulation and sterilization of growth medium and sterilization of the fermentation equipment. The cells are grown first as a stock culture (5 to 10 mL), then in a shake flask (200 to 1,000 mL), and then in a seed fermentor (10 to 100 liters). Finally, the production fermentor (1,000 to 100,000 liters) is inoculated. After the fermentation step is completed, the cells are separated from the culture fluid by either centrifugation or filtration. If the product is intracellular, the cells are disrupted, the cell debris removed, and the product recovered from the debris-free broth. If the product is extracellular, it is purified from the cell-free culture medium.
Although microorganisms can be grown in a number of different ways (batch, fed-batch, or continuous culture), it is most common to cultivate them in a batch fermentor. In batch fermentation, the sterile growth medium is inoculated with a suitable amount of microorganisms, and the fermentation, i.e cell growth, proceeds without any further addition of fresh growth medium. In some processes the cells themselves will be the product. In others the product is what the cells produce as they grow or as they are induced to produce. For example, in yeast manufacture the product is the biomass (cell) itself while in insulin manufacture, the product is formed as an intracellular product. In this case, the cells are disrupted to harvest the intracellular insulin and the cell debris is discarded.