Utilization of local agro‐residue substrates for fungal lipase production via solid‐state fermentation, optimization, and direct immobilization of crude enzyme

Abstract Fungal lipases exhibit superior thermal and stability characteristics but their high production cost limits their use. The use of agro‐residue oilseed cakes as a nutrient source in the growth medium can reduce the cost of enzyme production process. This study aimed to identify an optimal combination of fungal culture and substrate from locally available vegetable oilseed cakes (mustard, groundnut, almond, cottonseed, and coconut) for lipase production in solid‐state fermentation (SSF), and to optimize the process. The combination of Rhizopus oryzae NCIM 1212 with coconut oil cake was selected. Variables, such as the concentrations of NaNO 3 , KCl, K 2 HPO 4 , MgSO 4 , FeSO 4 , as well as pH, temperature, inoculum size, moisture content, and the addition of olive oil, were screened using a Plackett–Burman design. Significant variables, along with carbon and nitrogen sources, were further optimized using a one‐factor‐at‐a‐time approach. Inoculum size, KNO 3 , and moisture content were optimized through a central composite design. The highest lipase production (29.85 U g −1 ds (dry substrate), a 5.57‐fold increase) was achieved at KNO 3 2.10% w/w (weight by weight), inoculum size 1.17% v/w (volume by weight), and moisture content 66.79% w/w. Immobilization of the crude enzyme on functionalized magnetic nanoparticles resulted in protein loading of 67 ± 3 μg/mg and activity recovery of 59.15 ± 3.02%. This study provides insights into low‐cost enzyme production and its potential applications.