(Adapted from Van den Tweel et al., 1994, 7)
Enzyme sources including microorganisms, plant and animal tissue, cells, extracts and sub-cellular organelles can be thought to be used as a biocatalysts if they present the desired enzymatic activity. However, in the context of industrial exploitation the catalyst must be amenable to economic production in large scale, which implies culturable cells with short generation times, capable of growth on relatively inexpensive media.
Because of their rapid growth rates and ease of cultivation, bacteria, yeasts and filamentous fungi are currently the main source of enzymes and are likely to remain so.
In the selection of the biocatalyst for the pertinent bioconversion several questions must be answered once the starting material has been chosen:
Many proteins used in the food industry are only slightly purified from the natural state. However, one must destinguish categories of proteins in relation to their usage. As a dietary supplement of human and animal foods it is the aminoacid content one must regard. As a technological aid for baking, cooking and adhesives manufacture, it is the physical properties, such as elasticity, water retention and adhesion, one must explore.
When the protein of interest is an enzyme, the major concern is that the producing organism is able to secrete the target enzyme with a high yield, high activity, with only a few contaminating proteins (if no deleterious activities are added to the process, such as the proteolytic). In this way, the cost of the enzyme would be reduced.
After these criteria have been identified, several strategies can be followed to obtain suitable biocatalysts (with sufficient activity, selectivity and stability):
1) Selection of novel biocatalysts
2) The application of existing biocatalysts
3) Genetic modification of existing biocatalysts
When the enzyme of interest is not commercially available or more than one enzyme activities at the same time are desired (vd list of commercial enzymes and enzyme blends in reference [1]), national and regional culture collections may be the next step to access to known biocatalitic capabilities. However, it should be recognized that many of the microbes listed for particular catalytical activities have not been characterized accordingly.