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close this bookBioconversion of Organic Residues for Rural Communities (UNU, 1979)
close this folderPerspectives on bioconversion of organic residues for rural communities
View the document(introduction...)
View the documentIntroduction
View the documentSources of available nutrients
View the documentThe most suitable materials for bioconversion
View the documentCharacteristics of residues
View the documentBioconversion systems
View the documentPhysical and chemical treatments
View the documentMicrobial conversion
View the documentThe animal conversion phase
View the documentSummary
View the documentReferences

Sources of available nutrients

An inventory of nutrient sources is rather illuminating (see Figure 1). There are approximately 9,000 million ha of land in the world. Close to 50 per cent of this area consists of forests and shrub lands. Another 35 per cent is pasture and grassland, and 15 per cent is arable land. Of the produce grown on arable land, by far the major part is discarded as residue. This means that approximately 95 per cent of the land areas mentioned in Figure 1 could provide a source of nutrients yet untapped in the sense that their agricultural residues are not being utilized directly for human consumption.

Figure. 1. Land Production of Potential Nutrients

Food science and technology at present concentrate mainly on the 5 per cent of the annual production of potential nutrients that can be used after relatively simple forms of processing, such as cooking or baking. The 95 per cent residue needs considerable processing, be it physical, chemical, or via some form of bioconversion before it can be turned into suitable feed or food. This paper will concentrate on the products that we refer to as organic residues. They are what is left after agricultural production, sometimes left behind on the land (straw), on the farm (manure), or in agro-industries. They are relatively easily available for conversion into food.

Figure 2 shows some of the most important agricultural crops. There is a line along which we can divide these products. On the left side we find the percentage considered to be the main food component of the crops. They can be used without much processing by the human consumer (grain, oil, starch, vegetable protein). On the right side are the residues that comprise approximately two-thirds of the total production.

Figure. 2. Agricultural Crops

Two routes are available to convert these residues into useful products, as indicated in Figure 2: through feeding to animals, or by some industrial process.

Because these residues form the major part of agricultural production, their conversion into food via efficient and safe systems deserves far more attention than we have paid it so far.

Tremendous efforts are required to make such new systems operational. Therefore, we should concentrate on a limited number of the most promising ones and approach them in a multi-disciplinary fashion.

Those of us involved in developing new conversion systems will agree that the creation of acceptable food from novel sources usually requires animal conversion as a last step. Microbial conversion alone produces, in most cases, biomass, e.g., single-cell protein that is not accepted as a food by most consumers.