| Summary: | Three kinds of phenolic acid-grafted soluble soybean polysaccharide (SSPS) with similar grafting ratios were prepared, and their structure was characterized by FT-IR, UV-vis and <sup>1</sup> H NMR. The impact of phenolic acid on the antioxidant activity of SSPS was evaluated. Then, films were prepared by using phenolic acid-grafted SSPS. The physical, mechanical and biological performances of phenolic acid-grafted SSPS films were further investigated. The results indicated that an ester linkage was formed between the SSPS and phenolic acid. The grafting ratio of para-hydroxybenzoic acid, protocatechuic acid and gallic acid-grafted SSPS was 29.45, 31.76 and 30.74 mg/g, respectively. Phenolic acid endowed SSPS with improved antioxidant properties. Gallic acid (GA)-grafted SSPS possessed the best DPPH radical scavenging ability and reducing power, which may be related to the three phenolic hydroxyl groups in GA. Phenolic acid-grafted SSPS films showed increased moisture content and decreased water solubility compared to SSPS film. The phenolic acid-g-SSPS decreased the mechanical properties but enhanced the water vapor barrier property, and antioxidant and antibacterial properties of SSPS film. Meanwhile, the para-hydroxybenzoic acid-grafted SSPS film showed the lowest water vapor permeability (3.70 × 10<sup>−7</sup> g mm/h cm<sup>2</sup> Pa), and the GA-grafted SSPS film exhibited the best antioxidant and antibacterial activities.
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