Modelling of a simplified reactor for solid state fermentation of agricultural products or byproducts. Use of the fermented feed by pigs

In order to increase the crude protein content of agricultural surpluses or residues, solid state fermentation was investigated at laboratory and pilot levels. The barley example was described in detail. A simple and inexpensive process has been developed using a selected strain of Aspergillus niger which did not require any heat, acid or alcali pretreatment of the substrate. This process did not need the control of the culture parameters (pH, oxygen, moisture,...) except for the on-line temperature measurement which ensured the running of the proposed pilot reactor. This reactor was automated and well adapted to farm applications. The chemical composition of fermented barley showed a crude protein content of 26.5 per cent vs 11.1 per cent for barley at laboratory scale and 23.8 per cent vs 12.3 per cent at pilot scale. The true protein content of fermented barley was 20.0 per cent at laboratory scale and 13.2 per cent at pilot scale. This increase led to starch content reduction. The nutritive value of barley and Aspergillus niger fermented barley were determined by digestibility tests with growing pigs. Dry matter fecal digestibility, ileal apparent digestibility of crude proteins and of all the amino acids (except for proline) were increased by the fermentation. The metabolizable energy content of fermented barley was 3125 kcal per kg dry matter. A 70-day trial, involving 30 pigs, was set up to test the use of fermented barley as a substitute for the traditional protein feed. Two diets isonitrogenous and isoenergetic were compared. The former was based on barley and soya bean oil meal and the latter was a mixture of barley, fermented barley, and soya bean oil meal. Animal performances were similar. There was no significant difference in the dry matter or crude protein fecal digestibility, nitrogen balance or metabolisable energy in either diet (in vivo measurements).