However, protein enrichment by these methods does not exceed 3- 4 per cent, and therefore the end product is insufficient for use as a complete feedstuff. By mechanical stirring, the inoculated substrate spontaneously takes the form of well-separated and uniform granules of about one millimeter in diameter.
Aeration is performed by passing humidified air through the perforated bottom of the tank.
Conventional probes are used to monitor, by mixing and water-spraying, the temperature, pH, and moisture content. Up to now, all experiments have been performed with a selected strain of Aspergillus niger having high amylolytic activity and suitable amino-acid composition. However, it should be pointed out that other filamentous fungi could be utilized as well. This method of protein enrichment has already been used successfully with a variety of starchy materials, namely, cassava, whole potatoes, potato wastes from industrial facula works, and banana refuse. The results are summarized in Table 2, showing that after 30 hours of incubation, one obtains a product containing an average of 20 per cent true proteins, measured by the Lowry method, and 25 per cent residual reducing sugars.