UC Davis

Almond hulls are a byproduct of the almond industry and are typically used as cattle feed. They have a high fiber content but low protein content. Due to downsizing in the dairy industry and an increasing almond industry in California, demand for the hulls as dairy feed has decreased. However, poultry and aquatic industries are pursuing new materials for protein-rich feed supplements. Using a solid-state fermentation (SSF) conversion process, the hulls were used as substrate for filamentous fungi which increased the protein content of the hulls and resulting fermentation residue to the appropriate levels for animal feed supplements. The first objective in converting the hulls into protein-rich fungal biomass was to identify the optimal fungal strain for biomass production using the hulls as the substrate. The second objective was to optimize the SSF process using the optimal fungi identified through the first objective. After screening various fungi, Myceliophthora thermophila was identified as the optimal fungi for protein production capable of producing fermentation reside with a maximum crude protein content of 18.10%.Fermentation conditions for key parameters were optimized. The optimized fermentation condition for the M. thermophila strain was almond hull particle size (75-250 m), fermentation time (96 hours), and solid-loading (6.90% w/w). The fermentation residue produced contained 18.10% crude protein and 6.25% crude fat. The protein yield was 0.20 g crude protein/g carbohydrate consumed. The residue had good in vitro digestibility (80.37  7.06%) and contained a complete amino acid profile. The fermentation temperature and relative humidity were kept constant at 48-50C with relative humidity controlled at 70-90%. Therefore, the M. thermophila fermentation residue could potentially serve as a protein-rich supplement for poultry feed supplements. However, the fiber content of the residue is too high for direct use as an aquatic feed supplement. Additional procedures are needed to extract the protein from the fermentation residue for aquatic feeds.