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close this bookBioconversion of Organic Residues for Rural Communities (UNU, 1979)
View the documentFrom the charter of the United Nations University
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close this folderPerspectives on bioconversion of organic residues for rural communities
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View the documentSources of available nutrients
View the documentThe most suitable materials for bioconversion
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close this folderAvailability of organic residues as a rural resource
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View the documentDiscussion summary: Papers by van der Wal and Barreveld
close this folderMicro-organisms as tools for rural processing of organic residues
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View the documentMicrobial utilization of mono- and di-saccharide residues
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View the documentMicrobial utilization of cellulose and ligno-cellulose residues
View the documentAlgal culture as a source of biomass
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close this folderProduction of feed as an objective for bioconversion systems
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close this folderEnvironmental goals for microbial bioconversion in rural communities
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View the documentDiscussion summary: Papers by Porter, Berk and La Rivière
close this folderStrategies for developing small-scale fermentation processes in developing countries
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close this folderProduction of microbial protein foods on edible substrates, food by-products, and ligno-cellulosic wastes
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View the documentDevelopment of protein-rich vegetarian meat substitutes in the western world
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close this folderThe role of ruminants in the bioconversion of tropical byproducts and wastes into food and fuel
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View the documentNutritional limitations in the use of tropical by-products and waste
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View the documentAn integrated system for converting tropical feeds and byproducts into milk, beef, and fuel
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close this folderPossible applications of enzyme technology in rural areas
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close this folderIndian experience with treated straw as feed
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View the documentAnnex 1. The energy efficiency of the two-stage, feed-fuel processing of straw in indian villages
View the documentAnnex 2. Method of calculating the value presented in table 2 for the efficiency of naoh energy usage
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View the documentAnnex 4. Calculated efficiency of milk production by straw-fed village buffaloes
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close this folderIndian experience with algal ponds
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close this folderOrganic residues in aquaculture
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close this folderBiogas generation: developments. Problems, and tasks - an overview
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View the documentMicrobiology of CH4, or bio-methanogenesis
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close this folderMushroom production technology for rural development
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close this folderThe combination of algal and anaerobic waste treatment in a bioregenerative farm system
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close this folderA continuous composting system for disposal and utilization of animal wastes at the village level
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close this folderBioconversion of fruit and vegetable wastes
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close this folderIntegrated research on agricultural waste reclamation
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View the documentProduction of yeast from soybean cooking waste at miso factories
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close this folderSolid state fermentation of starchy substrates
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close this folderProduction of single-cell protein from cellulose
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close this folderAnalysis of energy cost of integrated systems
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close this folderAnalysis of bioconversion systems at the village level
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close this folderNutritional evaluation of bioconversion products for farm animals
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close this folderBioconversion products: toxicology - problems and potential
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close this folderNutritional evaluation in humans
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View the documentEvaluation of products of bioconversion for human consumption
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View the documentThe evaluation of various food products
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View the documentDiscussion summary: Papers by van Weerden, Shacklady, and Bressani
close this folderBiomass from organic residues for animal and human feeding
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close this folderAppropriate biotechnology - summary remarks
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The evaluation of various food products

Food Products Derived from Animals

Domestic animals such as ruminants, swine, and poultry will probably be fed more and more products containing materials from bioconversion processes. It is not expected, however, that this practice will change the quality of the protein derived from the animals. Changes in the chemical composition of animal tissues may occur, as well as deposition in the tissues of heavy metals, insecticide and herbicide residues, and other additives. If the levels of these substances become too high, the animals will show a decrease in overall performance, which, in turn, should lead to elimination of the product from the feed. If the animals gain weight and show good feed-conversion efficiency and overall performance, it is a good indicator that food products made from such animals will be of high enough quality to be used for human feeding. This, however, does not imply that quality control evaluation should not be carried out on food products obtained from animals fed bioconversion products or biomass (6).

TABLE 1. Protein Intake for Nitrogen Equilibrium Using the Conventional and Short-Term NBI (g/kg) in Adult Human Subjects

Protein source Conventional Short-term
Soy isolate 0.67 0.54
Milk 0.63 0.62
50/50 beef/soy 0.59 0 57
Beef 0.64 0.53

Source: Bressani et al. (8).

Conventional Fermented Foods

Fermented foods have been consumed for a long time by populations living in various parts of the world. Although there are several kinds, only three will be discussed in terms of protein quality. These are: (a) foods such as tempeh, a fermented food based on soybeans, a high-oil, high-protein seed; (b) fermented foods based on cereal grains, mainly rice, and (c) fermented foods based on starchy foods such as cassava.

The impact of the fermentation process on the protein quality of the end-product will be considered first. To predict its protein quality, it is essential to know the value of the starting material and the value of the biomass itself. In the case of tempeh, soybean protein is deficient in sulphur amino acids and rich in lysine. The biomass produced on it also contains protein deficient in sulphur amino acids and rich in lysine. Therefore, the protein quality of tempeh will be equivalent to the average of the protein content in the soybean and in the fermented biomass, depending on the amount of protein supplied by each source.

There are no data available on the protein quality of biomass produced on cereal grains. Cereal-grain protein, however, is deficient in lysine, while microbial protein is a rich source of this amino acid. Table 2 shows the nutritional impact of small amounts of yeast added to maize, wheat, and rice. In each case, there is a significant increase in protein quality, suggesting that production of biomass on cereal grains for human feeding would be beneficial to the consumer, assuming that the product would be acceptable organoleptically (9 - 11).

TABLE 2. Supplementary Effect of Small Amounts of Torula Yeast Added to Various Cereal Grains

Cereal grain Amount of

torula added

(%)

Protein quality

PER

Maize 0 1.23
  3 2.06
Whole wheat 0 1.81
  4 2.17
Wheat flour 0 0.82
  8 2.18
Rice 0 1.87
  6 3.13

Sources. Bressani and Marenco (9); Jarquin et al (10); Elias et al. (11).

There have been few nutritional studies on the protein value of biomass grown on starchy foods. Therefore, to predict its possible use, the analogy of supplementing cassava with beans will be used. SCP and legume foods are also deficient in sulphur amino acids and rich in lysine. The results in Figure 4 show that body weight in rats is maintained when cassava is supplemented with 30 per cent of beans, providing 7.5 9 of protein. However, when bean protein is supplemented with methionine, the body-weight gain of rats fed the bean-cassava diet is maintained with only 15 per cent of beans, providing about 4.5 9 of protein. These results imply that, in order to increase protein content in starchy foods by biomass production, the protein content should be higher than 8 per cent to maintain body weight in experimental animals.

Algae

Algae have been used as food for centuries. They form a part of the diet of the people living around Lake Chad in Africa, and were eaten by the Aztecs in Mexico. Among the several thousands of green and blue algae known, the following have been found adequate for large- or small-scale cultivation: the green algae, Chlorella vulgaris, Scenedesanus acutus, Coelastrum proboscideum, and the blue-green algae, Spirulina maxima. The following discussion of algae is based on information from other laboratories, as we have not gone beyond chemical and animal studies with Microcystis sp. (12).



Figure. 4. Nutritional Significance of Bean Protein Quantity and Quality to Cassava-Based Diets

TABLE 3. Some Observations Made on Human Subjects Fed Algae Protein (10 to 500 g/day)

Unacceptable smell
Disagreeable flavour
Poor appearance of food
Gastro-intestinal discomfort
Poor digestibility of nutrients
Nausea at high levels of intake
Urine and blood analyses normal
After additional processing:
More acceptable organoleptically
Gastro-intestinal problems persisted

Not many results have been reported recently on nutritional evaluation trials using algae grown on different types of biomass for human subjects. This is probably not due to a lack of interest in manufacturing such products, but rather to the initial results obtained in 1963 - 68 that showed a variety of adverse effects in subjects fed algae or other SCPs. As shown in Table 3, clinical trials with algae were particularly discouraging (13 - 17). Most materials containing algal protein showed low digestibility for most nutrients, and caused gastrointestinal discomfort. Unacceptable smell, taste, and disagreeable flavour produced nausea. However, it became evident that further processing by alcohol extraction improved the product significantly.

In more recent reports, materials produced and processed by improved technologies have yielded products that offer more promise. Some of these results are shown in Tables 4 and 5, indicating better protein digestibility and biological value, while urine and blood analyses are no different from those observed after feeding casein, a universally acceptable protein. However, it is costly to create acceptable foods from algae. These results suggest that the production of such materials for rural communities would be better directed towards animal feed, where they will be more beneficial to man in the long run.