Interaction between Aspergillus oryzae lipase and chitosan: The underlying mechanism and complex characterization

The complexation between Aspergillus oryzae lipase (AOL) and chitosan (CS) was investigated as a function of phase separation pH and the resultant complexes were characterized. The results indicated that AOL and CS could assemble micron-sized complexes in pHs 5.0–6.5 and the strongest interaction occurred in pH 5.5. QCM-D analysis revealed that association in pH 5.5 generated a viscoelastic hydrated adlayer with the largest thickness. ITC analysis indicated that the interaction between AOL and CS was driven by enthalpy and the highest one-site binding stoichiometry was recorded in pH 5.5, which was 1.3 and 7.9 times higher than in pHs 5.0 and 6.0, respectively. Both electrostatic attraction and hydrophobic interaction played dominant role in AOL-CS complexation. Compared with free AOL, the interaction with CS reduced its α-helix content, increased its β-sheet content, and changed its tertiary structure; besides, the AOL-CS complex assembled in pH 5.5 exhibited the highest contact angle up to 85.5° and demonstrated enhanced lipase activity retention after incubation in pHs 3.0–9.0 and temperatures 35–75 °C. Hence, the AOL-CS complexes could be used to construct novel biphasic catalysis media based on O/W Pickering emulsions.