Citric acid production from partly deproteinized whey under non-sterile culture conditions using immobilized cells of lactose—positive and cold-adapted Yarrowia lipolytica B9

• Citric acid production by cold-adapted microorganism could be achieved.
• A lactose-positive strain of Yarrowia lipolytica was used for citric acid production.
• A new non-sterile culture process for citric acid production was designed.

The present study was performed to produce citric acid (CA) from partly deproteinized cheese whey (DPCW) under non-sterile culture conditions using immobilized cells of the cold-adapted and lactose-positive yeast Yarrowia lipolytica B9. DPCW was prepared using the temperature treatment of 90 °C for 15 min. Sodium alginate was used as entrapping agent for cell immobilization. Optimum conditions for the maximum CA production (33.3 g/L) in non-sterile DPCW medium were the temperature of 20 °C, pH 5.5, additional lactose concentration of 20 g/L, sodium alginate concentration of 2%, number of 150 beads/100 mL and incubation time of 120 h. Similarly, maximum citric acid/isocitric acid (CA/ICA) ratio (6.79) could be reached under these optimal conditions. Additional nitrogen and phosphorus sources decreased CA concentration and CA/ICA ratio. Immobilized cells were reused in three continuous reaction cycles without any loss in the maximum CA concentration. The unique combination of low pH and temperature values as well as cell immobilization procedure could prevent undesired microbial contaminants during CA production. This is the first work on CA production by cold-adapted microorganisms under non-sterile culture conditions. Besides, CA production using a lactose-positive strain of the yeast Y. lipolytica was investigated for the first time in the present study.