Use of ion-exchange resins for purification of L-lactic acid-containing Rhizopus oryzae fermentation broth

Objectives. The work set out to describe conditions for the purification of a model fermentation broth for cultivating the lactic acid-containing micromycete Rhizopus oryzae from impurities of inorganic salts using ion-exchange resins under dynamic conditions. Methods. The solutions collected for analysis were examined using precipitation titration to determine the concentration of chlorides along with a qualitative reaction with Nessler’s reagent to ascertain the presence of ammonium ions. The concentration of lactic acid was evaluated spectrophotometrically using iron(III) chloride. The total nitrogen content was determined by high-temperature catalytic combustion on a Formacs HT TOC/TN Analyzer (Netherlands). The content of trace elements and macroelements in the samples was determined using an iCAP 6300 Duo inductively coupled plasma emission spectrometer (United Kingdom). Results. Purification of the model broth under the described conditions was carried out by successive filtration through the cation exchanger KU-2-8 in the H-form and subsequently through a mixture of weakly basic A847 and strongly basic AV-17-8 anion exchangers in the OH-form taken in a one-to-one ratio. The breakthrough of impurity ions into the solution was shown to occur after passing 30-fold and 10-fold volumes of the model broth relative to the volume of the cation-exchange and anion-exchange resins, respectively. The dynamic exchange capacity prior to breakthrough was determined as follows: 0.35 mmol-eq/cm3 for the anion-exchange column and 1.61 mmol-eq/cm3 for the cation-exchange column. The following parameters were defined as column regeneration modes: 3-fold excess of 2 M H2SO4, 10-fold excess of distilled H2O for cation exchange; for anion exchange, 3-fold excess of 2 M NaOH and 20-fold excess of H2O. Conclusions. The conducted studies showed that purification of the model fermentation broth of Rhizopus oryzae can be successfully implemented using ion-exchange resins. The model fermentation broth passing successively through cation-exchange and anion-exchange columns was shown to be purified from impurities of mineral salts while maintaining the concentration of lactic acid.