Alginate Application in Immobilized Biocatalysts
Using Biocatalysts such as enzymes or active whole cells is helpful to carry out many commercial chemical syntheses and conversions, such as the use of enzymes for the conversion of glucose to fructose, the use of whole cells for the conversion of starch to ethanol, and the continuous production of yoghurt, etc. In order to carry out these processes on a moderate to large scale, the biocatalysts must be concentrated and recoverable for re-use.
This can be achieved by "immobilizing" the enzymes or cells by entrapping them in a material that will still allow penetration by the substance to be converted or changed. Originally, single enzymes were isolated and used for a specific conversion, but now similar or better results can be obtained by using whole cells, and this is more economical. An added advantage of immobilization is that the cells last longer. Ordinary suspended cells may have good activity for only 1-2 days, while immobilized cells can last for 30 days. One of the first materials to be used for immobilization is beads made with calcium alginate. The whole cells are suspended in sodium alginate solution and this is added dropwise to a calcium chloride solution. The beads form in much the same way as described for artificial cherries. In use, they are packed into a column and a solution of the substance to be converted is fed into the top of the column and allowed to flow through the bed of beads containing the immobilized biocatalyst in the cells. The conversion happens and the product comes out at the bottom. A simple example is to immobilize yeast cells, flow a solution of sugar through the beads, and the sugar is converted to alcohol.