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close this bookBioconversion of Organic Residues for Rural Communities (UNU, 1979)
close this folderProduction of single-cell protein from cellulose
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Discussion

The experiments described in this paper clearly show that there are several approaches to the development of a successful technology for fermentation of cellulose. As mentioned earlier, cellulose occurs complexed with hemicelluloses and lignin in nature. Thus, if fermentation is to be developed on native ligno-cellulosics, we have to deal with at least three different types of carbon compounds as substrafes, namely, short-chain pentose polymers, complex aromatic polymers built from phenyl-propane units, and insoluble, large molecular linear polymer cellulose. In general, microbial growth on more than one substrate tends to lower the overall growth rate. Hence, the productivity of the fermentation may, in all probability, be lower on mixed substrates with a single organism (6) than on the different components of the mixture if used singly. However, the productivity on mixed substrates may be increased with a system of several microbes whose populations can coexist commensally or neutrally (15). With the latter approach it may be difficult to obtain, from fermentation, final products of uniform composition. In order to ensure the reproducibility of composition of the product, our efforts have been directed to examine microbial growth on treated cellulose with a single organism under aseptic conditions.

Of all the three systems of micro-organisms discussed, the technology for SCP production with Aspergillus has advanced farthest. Although our initial intention was to develop a lowlevel technology for producing fungal protein under non-sterile conditions, it became apparent that, with the present knowledge on cultivation of Aspergillus, it may be much more economical to produce SCP by continuous cultivation under aseptic environments. To date, this is the first report on continuous cultivation of a micro-organism for the production of SCP with 80 - 85 per cent assimilation of cellulose. It is almost tempting to speculate that, with further development of the process on the pilot fermenters, the problems of scaling up can easily be overcome and that the production of SCP from cellulose is on the verge of becoming a reality.