Studies On Citric Acid Production From Extract Of Jerusalem Artichoke Tubers By The Genetically Engineered Yeast Yarrowia Lipolytica Strain30

At present, citric acid (CA) is produced mainly by submerged fungalfermentation of sucrose or molasses or glucose medium using Aspergillus niger.However, the production of CA with the use A. niger is associated with theaccumulation of significant amounts of solid and liquid wastes. In recent years,Yarrowia lipolytica has been considered as another potential producer of CA.However, for economical aspect, it becomes important to further improve CAproduction by Y. lipolytica via genetic engineering. In our previous study, thegenetically engineered yeast Y. lipolytica30producing recombinant exo-inulinase inwhich ACL1gene encoding ATP-citrate lyase was deleted and the copy number of theICL1gene encoding iso-citrate lyase was increased was obtained. During the2-lfermentation,84.0g/l of citric acid in the fermented medium was attained from10.0%of inulin by the genetically engineered yeast Y. lipolytica30within214h. Inorder to reduce the cost for citric acid production, extract of Jerusalem artichoke wasused as the substrate for CA production by the genetically engineered yeast Y.lipolytica30in this study.“One-variable-at-a-time” method was used to optimize the conditions forextraction of sugar from Jerusalem artichoke tubers. The results showed that theoptimized extraction conditions were that the solid to liquid ratio was1:20，theextraction time was50min，the extraction temperature was100℃，the concentrationof HCl was0.05M，the extraction times was4. Extract of Jerusalem artichoke tuberstreated by Ca(OH)2was used to produce CA by Y. lipolytica30,24.3g L-1citric acidwas produced and the yield of citric acid was0.39g g-1within12d. However, theyield of CA was8.21g/l and the yield of citric acid was0.17g g-1when the crudeextract of Jerusalem artichoke was used. In this study, citric acid production from extract of Jerusalem artichoke tubers by thegenetically engineered yeast Yarrowia lipolytica strain30was investigated. After thecompositions of the extract of Jerusalem artichoke tubers for citric acid production wereoptimized, the results showed that natural components of extract of Jerusalem artichoketubers without addition of any other components were suitable for citric acid productionby the yeast strain. During10-l fermentation using the extract containing80g L-1totalsugars,68.3g L-1citric acid was produced within336h. At the end of the fermentation,9.16g L-1of residual total sugar and2.14g L-1of reducing sugar were left in thefermented medium. At the same time, citric acid in the supernatant of the culture waspurified. It was found that the purity of citric acid in the crystal was96%.