Biovalorization of Olive Mill Waste Water for the Production of Gellan Gum from Sphingomonas paucimobilis
Ioannis Giavasis *
Department of Food Technology, Technological Educational Institute of Thessaly, Lab. of Food Microbiology and Biotechnology, Greece
Konstantinos Petrotos
Department of Biosystems Engineering, Technological Educational Institute of Thessaly, Lab. of Food and Agricultural Engineering, Greece
*Author to whom correspondence should be addressed.
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.
Keywords: Gellan gum, Sphingomonas paucimobilis, olive mill waste water utilization, olive polyphenol, biovalorization, dephenolization and phenol degradation, bioprocess optimization, microbial polysaccharide