This last requisite creates a biotechnological difficulty that has been responsible for the failure of many previous attempts to achieve direct protein enrichment of starchy materials. In a mash of raw material dense enough to be directly utilized for animal feeding, the major problem is to maintain aerobic conditions and oxygen transfer efficiency so as to prevent anaerobic contamination of the culture. However, protein enrichment by these methods does not exceed 3 - 4 per cent, and therefore is insufficient for use as a complete feedstuff. All of the operations are conducted in a commercial dough mixer of ten kg capacity, modified for that purpose. After mechanical stirring, the inoculated substrate spontaneously takes the form of well separated and uniform granules of about 1 mm diameter.
Aeration is performed by passing humidified air through the perforated bottom of the tank.
Conventional probes are used to monitor, after mixing and water spraying, the temperature, pH, and moisture content. However, other filamentous fungi could be utilized as well. The initial moisture content is critical, with an optimum of 55 per cent. This method of protein enrichment has already been worked out with a variety of starchy materials, namely cassava, whole potatoes, potato waste from industrial starch works, and banana refuse. The rate of conversion of carbohydrates to protein is 20 to 25 per cent, corresponding to 40 to 50 per cent conversion into dry weight biomass.