Biovalorization of Olive Mill Waste Water for the Production of Gellan Gum from Sphingomonas paucimobilis

Abstract

Aims: The aim of this work was to investigate and optimize the potential of olive mill waste water (OMWW) to be utilized as a substrate for the production of gellan gum by Sphingomonas paucimobilis. Study Design: The study was divided in two phases, a preparatory phase for the removal of olive polyphenols and/or condensation of OMWW, and a bioprocessing-fermentation phase. Place and Duration of Study: The study was conducted at the TEI of Thessaly from January 2013 to August 2015. Methodology: OMWW was used as a fermentation substrate for production of gellan after dephenolization by microfiltration, thermal condensation, and addition of minerals/nitrogen sources and glycerol. S. paucimobilis was grown in this substrate under controlled process conditions in shake flasks and a 15 lt bioreactor. Biomass, gellan, sugars, phenol concentration and apparent viscosity of OMWW were evaluated. Results: The results show that although S. paucimobilis can degrade olive polyphenols in OMWW, the removal of polyphenols is beneficial to gellan synthesis. The condensation (2/1, i.e. to the half of its initial volume) of the dephenolized OMWW also improved gellan production as it offered more sugars for polysaccharide production. After both dephenolization and 2/1 condensation gellan production increased by 50%. Yeast extract (1 g/l) was the preferable nitrogen source supplementation as it stimulated both cell growth and gellan synthesis. Glycerol (5 g/l) increased gellan formation and viscosity of the fermentation broth, which may indicate a key role of glycerol in gellan biosynthesis. An agitation of 500 rpm and aeration of 1 vvm resulted in the highest gellan production of 9.5 g/l in 63 h in the optimized and fortified OMWW after dephenolization and condensation. At 500 rpm an intense aeration of 2 vvm increased cell growth at the expense of gellan formation and resulted in a reduced viscosity.  Conclusion: After dephenolization, condensation, addition of some nitrogen source and glycerol, OMWW can be utilized as a substrate for efficient gellan production.