|Bioconversion of Organic Residues for Rural Communities (UNU, 1979)|
|Possible applications of enzyme technology in rural areas|
The above examples illustrate the possibilities of using enzyme technology to achieve new or improved use of natural products such as starch and cellulose. In the example of starch hydrolysis, it is possible to produce a fermentable syrup that can be used to cultivate acceptable food and feed yeasts. The major limitation, however, is the lack of the required enzymes in the rural community.
In the second example, a fermentation directly on cellulase that will allow both accumulation of enzymes via saccharification and production of useful products is described. This approach is particularly exciting because it offers a method by which enzyme unavailability can be overcome. The micro-organisms that contain the desired sets of enzyme activity readily reproduce themselves. Therefore, it is possible to develop, via high technology in the laboratory, strains of micro-organisms that have the desired properties and then take these organisms into the field where they can be reproduced repeatedly and used on a local basis. In this manner, the microbial cell becomes the vehicle for transferring high technology to the community.
Examining further the example of cellulose hydrolysis, it is possible to develop a system for saccharification of cellulose for sugar production, or a system for the direct conversion of cellulose to ethanol, acetic acid, or lactic acid. Alternatively, it is possible to add a second microbial culture that would utilize the sugars released by C. thermocellum-mediated cellulose saccharification. The resulting mixed culture could be used to produce lactic acid for use as a food preservative, short-chain fatty acids for animal feeding, or solvents for use in extraction of oilseed meals. Furthermore, via genetic engineering, it should be possible to incorporate traits in these organisms to make them withstand the highly competitive environment encountered in the rural community. The increased ability to compete with indigenous organisms is important so that fermentations can be run with little or no sterilization, under conditions of variable pH and temperature, or in combination with other desired organisms.
The key question raised earlier, of how to transfer and propagate enzyme technology in the field, could be answered by using starter cultures either prepared at a central location or propagated by a serial transfer using techniques similar to those used for traditional food fermentations. An interesting alternative would be to take advantage of the concept of immobilized whole cells. For this purpose, one could use readily available inorganic supports, such as porous rocks. One may choose to use high carbonate rocks to exert some pH control of the fermentation, or simply volcanic rock with a high degree of porosity. The microorganisms present in the system would adsorb to, and become associated with, the solid phase so that after removal of the fermentation liquid the organisms would be left behind. This would serve to help build up a substantial active population of microorganisms, as well as serially transfer the desired population from fermentation to fermentation, even from family to family and village to village.