Valorization of fruit pomaces for glycosidic enzymes production via solid state fermentation

Agro-industrial fruit pomaces represent complex, nutrient-rich substrates that can support microbial enzymes production within circular bioeconomy frameworks. This study systematically compared grape, mango, orange, and pomegranate pomaces as solid substrates for glycosidic enzymes production (amylase, xylanase, pectinase) using 14 microbial strains under solid-state fermentation conditions with the aim of identifying an efficient microorganism-substrate system that produces the highest glycosidic enzyme activity. For the 14 strains studied, Candida guilliermondii NRRL Y-2075 yielded the highest reported amylase activity (4344.67 U/gds) when cultivated on pomegranate pomace with no detectable activity in the unfermented pomace. Response surface methodology (RSM) based on a central composite design was subsequently applied to identify the optimal operational region for amylase production by evaluating pH, inoculum size, incubation temperature and time. Maximum amylase activity (4839.05 U/gds) was obtained at pH 5.6, 12.2% inoculum size, 30.7 °C incubation temperature, and 24 h of incubation. Experimental validation closely matched model predictions. Additional one-factor-at-a-time experiments demonstrated that supplementation with external carbon, nitrogen, amino acids, or metal ions did not enhance enzyme production, indicating that pomegranate pomace alone provides sufficient nutrients for efficient amylase synthesis. Collectively, the results suggest that pomegranate pomace can function as a nutritionally sufficient SSF substrate, reducing process complexity and supplementation requirements for sustainable amylase production.