Isocitric Acid Production from Ethanol Industry Waste by Yarrowia lipolytica

Abstract

There is ever increasing evidence that isocitric acid can be used as a promising compound with powerful antioxidant activity to combat oxidative stress. This work demonstrates the possibility of using waste product from the alcohol industry (so-called ester-aldehyde fraction) for production of isocitric acid by yeasts. The potential producer of isocitric acid from this fraction, Yarrowia lipolytica VKM Y-2373, was selected by screening of various yeast cultures. The selected strain showed sufficient growth and good acid formation in media with growth-limiting concentrations of nitrogen, sulfur, phosphorus, and magnesium. A shortage of Fe2+ and Ca2+ ions suppressed both Y. lipolytica growth and formation of isocitric acid. The preferential synthesis of isocitric acid can be regulated by changing the nature and concentration of nitrogen source, pH of cultivation medium, and concentration of ester-aldehyde fraction. Experiments in this direction allowed us to obtain 65 g/L isocitric acid with a product yield (YICA) of 0.65 g/g in four days of cultivation.

Effect of Metabolic Regulators and Aeration on Isocitric Acid Synthesis by Yarrowia lipolytica Grown on Ester-Aldehyde Fraction

“…The study was carried out with wild strain Y. lipolytica VKM Y-2373 previously selected as a producer of ICA from ether-aldehyde fraction (EAF) [36]. The culture was maintained at 4 • C on agar slants with n-alkanes.…”

“…For biomass assay, the cells were separated from the cultural broth through a paper filter and dried at 105 • C to a constant weight. Concentration of NH 4 + was determined potentiometrically as described earlier [36]. The concentration of residual ethanol was analyzed by gas-liquid chromatography as described earlier [36].…”

“…Concentration of NH 4 + was determined potentiometrically as described earlier [36]. The concentration of residual ethanol was analyzed by gas-liquid chromatography as described earlier [36]. Isocitric and citric acids were analyzed by HPLC and enzymatically as described earlier [36].…”

“…Since purification of EAF has considerable cost, the utilization of this by-product to produce ICA using yeast Y. lipolytica is of great environmental and economic importance. Using EAF as the only carbon source, we achieved 65 g/L ICA with a product yield of 0.65 g/g by optimizing culture conditions such as pH, ammonium sulfate, and EAF concentrations [36]. However, these indexes were lower than in the medium with pure ethanol [24,28].…”

“…Recently, we published the first paper on ether-aldehyde fraction (EAF) as a promising source of carbon for ICA synthesis by Y. lipolytica [36]. EAF (the head fraction of ethyl alcohol) is a by-product of ethanol industry.…”