Effect of Salt Addition upon the Production of Metabolic Compounds by Yarrowia lipolytica Cultivated on Biodiesel-Derived Glycerol Diluted with Olive-Mill Wastewaters

Markella Tzirita,Apostolis A Koutinas,Maria Kremmyda,Dimitris Sarris,Seraphim Papanikolaou

doi:10.3390/en12193649

Abstract

One of the major environmental problems is the highly toxic agro-industrial waste called olive mill wastewater (OMW), deriving from olive oil production. On the other hand, the continuous development of the biological liquid fuel industry (biodiesel and bioethanol) makes it mandatory the process and exploitation of their main by-products, crude glycerol. This study dealt with the biotechnological conversions of biodiesel-derived crude glycerol with the use of the non-conventional yeast Yarrowia lipolytica in media that had been diluted with OMWs. OMWs, employed as simultaneous liquid medium and substrate, is a new trend recently appearing in Industrial Biotechnology, where value-added metabolites could be produced with simultaneous partial detoxification (i.e. decolorization and phenol removal) of the used residue. In the present study, diluted OMWs (containing 2.0 g/L of total phenolic compounds) blended with 70.0 g/L crude glycerol were employed as substrates. Production of value-added compounds by Y. lipolytica strain ACA-YC 5031 was studied in nitrogen-limited media favoring the production of secondary metabolites (i.e. citric acid, polyols, microbial lipids, polysaccharides). Batch-flask cultures were carried out and the impact of the addition of different NaCl concentrations (1.0%, 3.0%, 5.0% w/w) added upon the biochemical behavior of the strain was studied. Remarkable biomass production was observed in all trials, while in the “blank” experiment (no OMWs and no salt added), the metabolism was shifted toward the synthesis of polyols (Σpolyols = mannitol + arabitol + erythritol > 20 g/L and maximum total citric acid-Cit (sum of citric and isocitric acid) = 10.5 g/L). Addition of OMWs resulted in Citmax = 32.7 g/L, while Σpolyols concentration dropped to <15 g/L. Addition of salt in the OMW-based media slightly reduced the produced biomass, while Cit production drastically increased, reaching a final value of 54.0 g/L (conversion yield of Cit produced per unit of glycerol consumed = 0.82 g/g) in the trial with addition of 5.0% NaCl. Finally, significant color and phenols removal were observed, evaluating the yeast as a decontamination medium for the OMW and a great candidate for the production of value-added compounds.

Highlights

Olive-mill wastewaters (OMWs), the major effluent deriving from the olive oil production process, are considered as one of the most challenging agro-industrial wastes to treat, since they are produced in very high quantities
The present study investigated the ability of Y. lipolytica strain ACA-YC 5031, a strain that has been reported capable of producing SCO and citric acid during growth on glucose-based media under nitrogen-limited conditions [53], to grow and produce secondary metabolites on mixed nitrogen-limited media consisting of OMWs and biodiesel-derived glycerol
Batch Fermentations and Production of Value-Added Compounds by Yarrowia lipolytica Growing on OMW/Glycerol Blends Supplemented with NaCl

Summary

Introduction

Olive-mill wastewaters (OMWs), the major effluent deriving from the olive oil production process, are considered as one of the most challenging agro-industrial wastes to treat, since they are produced in very high quantities. Their strong odor and dark color and their relatively high organic load have a direct negative impact on the environment if they are released untreated. This important residue of the olive oil industry is one of the most difficult to treat wastes because of its high content in phenolic compounds [1,2]. Value-added metabolites could be produced during these fermentation processes with simultaneous partial detoxification (i.e. decolorization and phenol removal) of the residue [2,3,4,9,10,11]

Methods

Discussion

Conclusion