Abstract: 【Objective】The composite membrane liquids based on chitosan (5%, w/v) and varying apple polyphenols concentrations were developed in this work, and the composite membrane liquids with different polyphenol concentrations were fully investigated including their antioxidant activity, rheological properties and thermal stability. This result could provide theoretical basis for food preservation. 【Method】 The composite membrane liquids were prepared by adding different amounts of apple polyphenols (0.5%, 1.0% and 1.5%, respectively). Besides, effects of the different addition amounts of apple polyphenols on the antioxidant activity of the composite membrane fluids were measured. A controlled-strain rheometer was used to investigate static rheological properties of the composite membrane liquids, including the relationships between G′ and G″. The potential interactions between chitosan and apple polyphenols and the crystal structure of the composite membrane were characterized by Fourier transform infrared spectrum (FTIR) and X-ray diffraction, respectively. In addition, thermogravimetric (TG) and derivative thermogravimetric (DTG) analyses were conducted by using a thermal analysis equipment to characterize the thermal stability of the lyophilized composite membrane samples.【Result】The addition of apple polyphenols could significantly improve the antioxidant activities of the chitosan membrane liquid (P<0.01). The increase of apple polyphenols concentrations could lead to the increased antioxidant ability of the composite membrane liquids. When the apple polyphenols addition was 0.5%, the DPPH scavenging rate, inhibition capacity of lipid oxidation and OH radical scavenging rate were determined to be 41.33%, 56.32%, 35.44%, respectively. As the addition amount of apple polyphenols was increased to 1.5%, the antioxidant ability of the composite membrane liquids increased to 94.3%, 95.9%，98.4%, respectively, significantly higher than that of 0.5% polyphenol-incorporated composite membrane liquid (P<0.01). Compared to the BHT (1.5%), antioxidation properties of the composite membrane liquids with 1.5% apple polyphenols were higher (P<0.01). Moreover, the rheological analyses suggested that the composite membrane liquid was non-Newton pseudoplastic liquid (n<1，R2>0.99). With the increase of shear rate, the viscosity of the composite membrane liquids displayed an initially decrease but then a relatively stable trend (approximately 5 Pa·s). Meanwhile, the incorporation of apple polyphenols enhanced the viscoelastic property of the composite membrane liquids. Dynamic rheology of the composite membrane liquid transformed from G′G″. The results of FTIR and X-ray showed that the intermolecular interactions of apple polyphenols (-OH) and chitosan (-OH, -NH2) were formed, resulting in the slight change of absorption peak of the composite membrane at 3 400 cm-1, 1 545 cm-1 and 1 245 cm-1 and resulting in the reduced crystallinity of chitosan. According to the result of thermal analysis, thermal stability of the composite membrane liquids increased, probably due to the hydrogen bonds formed via the linkages between apple polyphenols and chitosan.【Conclusion】The composite membrane liquids prepared by adding apple polyphenols into the chitosan had higher antioxidant capacity, viscosity and thermal stability, thus could be used as a potential edible coating material for food preservation.

Key words: chitosan, apple polyphenols, antioxidant capacity, rheological properties, thermal stability