生物工程下游技术-第一章节幻灯片

第一章 生物反应器 Bioreactor,Section One,A bioreactor is a vessel in which is carried out a chemical process which involves organisms or biochemically active substances derived from such organisms. Bioreactors are commonly cylindrical, ranging in size from some liter to cube meters, and are often made of stainless steel.,Bioreactor,Bioreactor design is quite a complex engineering task. Under optimum conditions the microorganisms or cells will reproduce at an astounding rate. The vessel's environmental conditions like gas (i.e., air, oxygen, nitrogen, carbon dioxide) flow rates, temperature, pH and dissolved oxygen levels, and agitation speed need to be closely monitored and controlled.,One bioreactor manufacturer, Broadley-James Corporation, uses vessels, sensors, controllers, and a control system, digitally networked together for their bioreactor system.,1. Introduction,Crude medicinal preparations that were aqueous or alcoholic extracts of plant materials were known for centuries to practitioners of the indigenous methods of medicine.,The pain-killing salicylates and antimalarial compounds extracted from the bark of certain trees are notable examples of older medicines. Similarly, animal organs such as the pancreas, placenta, and the urine of pregnant females have been a source of hormones for therapeutic use.,Until recently, human albumin was manufactured from pools of human placenta collected from Third World countries. But the high risk of virus contamination from unidentified donors of placenta and the impracticality of identifying the donors, forced the discontinuation of this process. Today, plasma from unpaid donors is the major source of albumin and the risk of transmission of viruses calls for extensive purification including the use of dedicated virus removal and inactivation steps to render the product safe for human use.,Although crude preparations from plant or animal sources are still used as medicinals in some parts of the world, modern medicines in most countries are extremely pure. The high level of drug safety and purity are demanded by the regulatory authorities in such countries as the United States, Europe, and Japan. Fortunately, the biopharmaceutical industries are able to meet the stringent demands because they have access to a variety of excellent purification techniques.,The science of biotechnology covers the exploitation of microorganisms and cell cultures, which form the major source of high value compounds. More recently, geneticists have succeeded in breeding transgenic sheep and goats, and methods have been developed to get these animals to express the desired products in their milk. The industry today manufactures on a large scale compounds that would otherwise have been difficult, if not impossible, to produce in significant quantities for treating many diseases.,Whether produced from plants, animal tissue, microorganisms, or from cell culture, the desired products are present in rather complex process streams and need extensive purification. A great majority of these products are proteins, which makes this task even more difficult. If these were nonprotein molecules, such as antibiotics for example, one could use simpler solvent extraction methods to isolate the compounds from the solutions in which they are present.,Thus, in the biotechnology industry, there is quite a challenge to the biochemists and chemical engineers in the downstream processing departments of the companies. They employ diverse purification methods in the research laboratory at the bench scale and these are eventually scaled up to the production floor. The methods are used in complementary fashion to develop cost-effective methods in quick time and enable the companies to bring the products to market ahead of their competitors.,This chapter attempts to give the reader an overview of the techniques available for downstream purification of biotechnology products. Readers are advised to refer to specific chapters in later sections of this volume where these techniques are described in detail.,As stated before, the industry manufactures products from a number of sources and their downstream processing varies not only from product to product, but also varies depending on the source of the product. Each process, therefore, needs to be finely tailored depending on the properties of the product and the process stream from which it is recovered and purified.,2. Manufacturing Processes in the Industry,2.1. Products of Recombinant Bacterial Fermentation,The first step in these processes is the separation of the biomass from its surrounding broth. The protein of interest is expressed within the cell as a soluble protein, but it is quite often present in the form of an insoluble refractive mass called the “inclusion bodies.”,The recovery of the biomass is sometimes performed by preparative centrifugation, but the preferred method today is by means of tangential-flow filtration systems using microporous membranes of appro