Olive pomace valorization by Aspergillus species: lipase production using solid-state fermentation

Abstract

Background Pollution by olive mill wastes is an important problem in the Mediterranean area and novel solutions for their proper management and valorization are needed. The aim of this work was to optimize a solid-state fermentation (SSF) process to produce lipase using olive pomace (OP) as the main source of nutrients by several Aspergillus spp. Optimized variables in two different designs were: ratio between olive pomace and wheat bran (OP:WB), NaNO3, Czapek nutrients, fermentation time, moisture content (MC) and temperature. Results Results showed that the mixture OP:WB and MC were the most significant factors affecting lipase production for all fungi strains tested. With MC and temperature optimization, a 4.4-fold increase in A. ibericus lipase was achieved (90.5± 1.5 U g-1), using a mixture of OP and WB at 1:1 ratio, 0.02 g NaNO3 per g dry substrate, absence of Czapek nutrients, 60% of MC and incubation at 30 °C for 7 days. For A. niger and A. tubingensis, highest lipase activity obtained was 56.6± 5.4 U g-1 and 7.6± 0.6 U g-1, respectively. Conclusion A. ibericus was found to be the most promising microorganism for lipase production using mixtures of OP and WB.