Partitioning of protease from stomach of albacore tuna (Thunnus alalunga) by aqueous two-phase systems

Partitioning of protease from stomach of albacore tuna using an aqueous two-phase system (ATPS) was investigated. The best ATPS conditions for protease partitioning from stomach extract (SE) and acidified counterpart (ASE) were 25% PEG1000–20% MgSO4 and 15% PEG2000–15% MgSO4, which increased the purity by 7.2-fold and 2.4-fold with the recovered activity of 85.7% and 89.1%, respectively. Electrophoretic study revealed that SE had a major protein with a molecular weight (MW) of 40.6 kDa, while protein with MW of 32.7 kDa was predominant in ASE and ATPS fractions. Pepsinogen in SE might be activated to pepsin by acidification and partitioning process. SE was quite stable at 0 and 4 °C up to 14 days. The loss in protease activity in ASE and selected ATPS fractions was more pronounced when storage time and temperature increased. Therefore, ATPS can be effectively used to recover and purify protease from albacore tuna stomach.