Faculty of Food Technology and Biotechnology, University of Zagreb
Abstract
The possibility of using glycerol and glycerol-containing waste from biodiesel manufacture as a carbon and energy source for microbiological production of citric acid has been studied. Acid formation on the selective media had previously been tested in 66 yeast strains of different genera (Candida, Pichia, Saccharomyces, Torulopsis and Yarrowia). Under growth limitation by nitrogen, 41 strains (belonging mainly to species Yarrowia lipolytica) produced acids; unlike 25 strains of the genera Debaryomyces, Candida, Pichia, Saccharomyces and Torulopsis. Among the 41 acid-producing strains, mutant strain Yarrowia lipolytica N15 was selected since it was able to produce citric acid presumably in high amounts. The citric acid production by the selected strain was studied in dependence on the medium pH, aeration and concentration of glycerol. Under optimal conditions, the mutant Y. lipolytica N15 produced up to 98 g/L of citric acid when grown in a fermentor with the medium containing pure glycerol, and 71 g/L of citric acid when grown on glycerol-containing waste. The effect of growth phases on physiological peculiarities of the citric acid producer was discussed.Ispitana je mogućnost uporabe glicerola i otpada bogatoga glicerolom, dobivenih pri proizvodnji biodizela, kao izvora ugljika i energije za mikrobnu proizvodnju limunske kiseline. Prethodno je ispitana proizvodnja limunske kiseline na selektivnim podlogama pomoću 66 sojeva kvasaca različitih vrsta (Candida, Pichia, Saccharomyces, Torulopsis i Yarrowia). Pri smanjenim koncentracijama dušika 41 soj (uglavnom vrste Yarrowia lipolytica) mogao je proizvesti limunsku kiselinu, dok 25 sojeva vrsta Debaryomyces, Candida, Pichiа, Saccharomyces i Torulopsis to nije moglo. Od 41 soja odabran je mutant Yarrowia lipolytica N15, jer je mogao proizvesti veliku količinu limunske kiseline. Ispitan je utjecaj pH-vrijednosti podloge, prozračivanja tijekom reakcije i koncentracije glicerola u podlozi na proizvodnju limunske kiseline pomoću toga soja. U optimalnim uvjetima u fermentoru mutant Yarrowia lipolytica N15 proizveo je do 98 g/L limunske kiseline na podlozi sa čistim glicerolom, a do 71 g/L limunske kiseline na podlozi s otpadom bogatim glicerolom. U radu se raspravlja i o utjecaju faze rasta na fiziološke značajke kvasaca pri proizvodnji limunske kiseline
