Non-supplemented aqueous extract from dry olive mill residue: A possible medium for fungal manganese peroxidase production

The low moisture content of the dry olive mill residue (DOR), solid waste from the two-phase olive oil extraction process, enables its long-term storage and its ready reconstitution with water thus leading to a candidate liquid growth medium for the microbial production of enzymes of commercial interest. To test this hypothesis, two white-rot fungi (WRF), namely Lentinus tigrinus CBS 577.79 and Phlebia sp. DABAC 9, were grown in shaken cultures on non-supplemented aqueous extracts of the dry olive mill residue (ADOR) and compared for their ability to grow therein and produce Mn-dependent peroxidase (MnP). Then, in order to assess the feasibility of scale transfer to the reactor level, the two fungi were grown in a 3-L bubble-column reactor on 25% (w/v) ADOR at 28 °C and an aeration rate of 0.3 vvm. Under these conditions, L. tigrinus and Phlebia sp. produced 42.60 ± 1.74 and 38.88 ± 1.68 nkatal mL−1 MnP with respective mean volumetric productivities of 222.9 and 324.1 nkatal L−1 h−1. These results clearly show that the use of non-supplemented ADOR as a production medium enables a significant MnP production thus representing an excellent basis for process optimization.

► Aqueous dry olive mill residue is a valuable growth medium for MnP production.
► In a column reactor, Lentinus tigrinus and Phlebia sp. produced 43 and 39 nkatal mL−1 MnP.
► MnP activities and productivities obtained in this study are very promising.