Thermoseparating aqueous two-phase system for lipase recovery and partitioning from Nile tilapia viscera: Biochemical properties and effect of ultrasound

Abstract

Lipase from Nile tilapia (Oreochromis niloticus) viscera were partitioned and recovered using a thermoseparating aqueous two-phase system (T-ATPS). Different phase partitioning parameters, including type and concentration of salts, concentration of EOPO, NaCl addition, the EOPO phase/distilled water ratio and temperature were optimized. In the primary ATPS, lipase was satisfactorily partitioned to the EOPO-rich top phase in the optimum system composed of 20% crude enzyme, 40% EOPO 3900, 10% (NH4)2SO4 and 4% NaCl. In the secondary ATPS, the optimum ratio between the EOPO-rich top phase and distilled water was 1:1 (w/w) and the optimum temperature for inducing phase separation was 60 °C. After thermoseparation, water solution containing lipase and EOPO were formed in the top and bottom phase of this step, respectively. Under the optimal partitioning condition, the yield (64.45%) and purification fold (PF: 6.30-fold) were obtained. Additionally, the lipases retained in the salt-rich bottom phase in the primary ATPS were successfully recovered from the recycling step no more than three times. The total yield of 93.59% was obtained from this separation system. The partitioned enzyme exhibited optimal activity at pH 8.5 and 40 °C and was stable at a temperature range of 0–40 °C and a pH range of 8–10. It showed high tolerance in the presence of ethanol and methanol. The effect of ultrasound on the partitioned lipase activity was also studied. The highest lipase activity was achieved when the sample was treated with ultrasound at 180 W and 24 kHz for 20 min at 40 °C, under which the activity was increased by 110.73% over the control. Therefore, the T-ATPS was found to be an attractive technique for the recovery and partial purification of lipase from Nile tilapia viscera. Also, ultrasound could obviously improve its activity.