Production of racemic acetoin by fermentation using Lactobacillus casei

An aqueous two-phase system (ATPS) was used to extract enantioenriched acetoin produced by Lactobacillus casei using an isopropyl alcohol/potassium carbonate mixture. Saturation of the aqueous layer with potassium carbonate (40% w/w) at 50 °C with stirring for 2 h led to racemization of acetoin with a 50/50 ratio of the R/S enantiomers, respectively. Racemization of acetoin was found to be dependent primarily on increasing pH, while elevated temperatures (50 °C) also had an effect on the rate of racemization of acetoin in alkaline environments. Extraction with isopropyl alcohol (35% v/v), allowed a recovery of 94.3% of acetoin after 12 h of separation time. This paper shows that natural enantioenriched acetoin produced by fermentation is susceptible to racemization when an ATPS is used for downstream processing.