Faculty of Food Technology and Biotechnology, University of Zagreb
Abstract
Pure and crude glycerol from biodiesel production have been used as substrates for citric acid production by acetate-negative mutants of Yarrowia lipolytica in fed-batch fermentation. Both the final concentration and the yield of the product were the highest when Y. lipolytica Wratislavia AWG7 strain was used in the culture with pure or crude glycerol. With a medium containing 200 g/L of glycerol, production reached a maximum of citric acid of 139 g/L after 120 h. This high yield of the product (up to 0.69 g of citric acid per gram of glycerol consumed) was achieved with both pure and crude glycerol. Lower yield of citric acid in the culture with Y. lipolytica Wratislavia K1 strain (about 0.45 g/g) resulted from increased erythritol concentrations (up to 40 g/L), accumulated simultaneously with the citric acid. The concentration of isocitric acid, a by-product in this fermentation, was very low, in the range from 2.6 to 4.6 g/L.Čisti i sirovi glicerol, nastali pri proizvodnji biodizela, upotrijebljeni su kao podloga za dobivanje limunske kiseline šaržnim uzgojem acetat-negativnog mutantnog soja kvasca Yarrowia lipolytica. Najveći prinos i najveća konačna koncentracija produkta postignuti su uzgojem soja Y. lipolytica Wratislavia AWG7 na podlozi od čistog ili sirovog glicerola. S 200 g/L glicerola u podlozi nakon 120 sati uzgoja dobivena je maksimalna koncentracija limunske kiseline od 139 g/L. Tako visok prinos (do 0,69 grama limunske kiseline po gramu iskorištenoga glicerola) postignut je s obje podloge. Manji prinos limunske kiseline (0,45 g/g) dobiven je s pomoću soja Y. lipolytica Wratislavia K1, zbog povećanja koncentracije eritritola (do 40 g/L) koji se nakupljao usporedo s limunskom kiselinom. Prijašnjim je istraživanjem utvrđeno da pri proizvodnji limunske kiseline nastaje i vrlo mala koncentracija izolimunske kiseline (2,6-4,6 g/L)
