Statistical optimization of culture medium for neutral protease production by Aspergillus oryzae. Comparative study between solid and submerged fermentations on tomato pomace

A comparative study of the production of neutral protease was carried out by the cultivation of Aspergillus oryzae NRRL 2220 in solid-state fermentation (SSF) and submerged fermentation (SmF) using tomato pomace based medium. For this purpose, medium optimization was achieved using two experimental designs. The first, corresponded to the Plackett and Burman design with N = 8 experiments and k = N − 1 factors; five real (wheat bran, casein, NH4NO3, NaCl and ZnSO4) and two errors. Statistical analysis of the results allowed the selection of two factors having a significant effect on enzyme production (casein and NaCl in SSF, wheat bran and NaCl in SmF). Optima of the selected factors have been determined through a second experimental design, the central composite design of Box and Wilson with two factors; 19.79 g/L casein and 0.92 g/L NaCl for SSF and 17.92 g/L wheat bran and 1.18 g/L NaCl for SmF were found. The optimal production time of the neutral protease determined from the kinetic study was 96 h leading to 21309 U/g in SSF and 2343.5 U/g in SmF. The comparison of the proteolytic activities of the optimized media demonstrated a ratio of 9 between SSF and SmF, showing the efficiency of the solid-state fermentation compared to the submerged fermentation. The results confirmed the high biotechnological potential of this fungal strain for neutral protease production in solid-state fermentation. Additionally, the utilization of tomato pomace constitutes an efficient and inexpensive agro industrial substrate for protease production via the SSF approach and a suitable mean for its valorization and to reduce its ecological impact.