|Bioconversion of Organic Residues for Rural Communities (UNU, 1979)|
|Perspectives on bioconversion of organic residues for rural communities|
Alkali-treated straw can be given to small fermentation "plants" located in the rumens of cows, buffaloes, or goats The micro-organisms in these rumens are able to convert the treated residue into protein. The process has been fairly stable through the ages.
Microbial conversion can also be carried out outside the animal through fermentation processes By applying appropriate technology, we should then be able to produce protein products that could be converted into food by monogastric animals like poultry and pigs
If the micro-organisms used remain combined with the remnants of the organic residue that was used as a substrate, we call the product microbial biomass product (MBP). If the micro organisms are harvested and separated from the substrate, we refer to the product as single cell protein (SCP) The composition of SCPs compares favourably with the substrates on which they are grown, as shown in Table 6.
TABLE 6. Comparison of Chemical Composition (%) of SCP with Soybean Oilmeal
|Crude protein (N x 6.25)||60||74||32||52||45|
|True protein (amino acid- N x 6.25)||47||55||22||46||38|
Crude protein content and amino acid composition (Tables 6 and 7) put bacteria, yeasts, fungi, and algae into the category of high quality protein sources such as soybean oilmeal.
TABLE 7. Amino Acid Composition (9/16 9 N) of SCPs and Soybean Oil meal
|Methionine + cystine||2.9||3.1||2.5||3.2||2.9|
|Phenylalanine + tyrosine||7.9||6.2||8.1||6.0||8.4|
The digestibility of SCP (Table 8) again compares well with conventional high-quality protein sources like soya. Digestibility is lower for algae, and the data are inconclusive. Further evaluation is required.
TABLE 8. Digestibility Coefficients in Pigs
|Metabolizable energy (kcal/kg)||3,860||3,720||2,940||-||3,190|
It is often assumed that small-scale SCP production can be made operational relatively easily. This is a serious under-estimation of the problems involved. Development of low-key technology that can operate on the scale of a farm co-operative or a village, and that is nevertheless effective and stable, requires elaborate research efforts. Positive results are more likely to be achieved if experienced industrial fermentation research groups participate.