Growth of Rhizopus sp. on ungelatinized cassava flour in solid state fermentation for protein enrichment

In order to study the potential of bioconversion of crude cassava flour, without gelatiization, it was necessary to apply a preliminary treatment to eliminate the natural microflora (bacteria, yeast and fungal spores), without allowing starch gelatinization, which otherwise would occur in steam sterilization process. Studies on the effect of temperature and moisture content of flour on micro-organisms content and rate of starch gelatinization, allowed the optimization of a dry or semi-dry treatment of cassava flour to obtain a micro-organism-free ungelatinized crude flour. The pretreated flours, as such or after mixing (50/50) with crude soya flour, were inoculated with spores suspension of selected strains of Rhizopus sp. (oryzae, arrhizus, oligosporus), and incubated in a column reactor, equipped for on line respirometric analysis in solid state fermentation. The efficiency of each strain, in terms of specific growth rate, protein enrichmen and sugars bioconversion, was determined. Crude cassava flour could be enriched with up to 14% of protein, in contrast to that of 20%, in case of 50/50 mixture of crude cassava and soya flours. The protein enrichment of cassava by Rhizopus sp. is of commercial importance due to GRAS clearance of this fungi.