Polyphenols and polysaccharides are very important natural products with special physicochemical properties and extensive biological activities. Recently, polyphenol-polysaccharide conjugates have been synthesized to overcome the limitations of polysaccharides and broaden their application range. Grafted copolymers are produced through chemical coupling, enzyme-mediated, and free radical-mediated methods, among which the free radical-induced grafting reaction is the most cost-effective, ecofriendly, safe, and plausible approach. Here, we review the grafting reactions of polysaccharides mediated by free radicals with various bioactive polyphenols, such as gallic acid (GA), ferulic acid (FA), and catechins. A detailed introduction of the methods and their mechanisms for free radical-mediated grafting is given. Structural characterization methods of the graft products, including thin-layer chromatography (TLC), ultraviolet-visible (UV-vis) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR) analysis, and X-ray diffraction (XRD) are introduced. Furthermore, the biological properties of polyphenol-polysaccharide conjugates are also presented, including antioxidant, antibacterial, antidiabetic, and neuroprotection activities, etc. Moreover, the potential applications of polyphenol-polysaccharide conjugates are described. Finally, the challenges and research prospects of graft products are summarized.

Anthocyanin-rich steamed purple sweet potato (SPSP) is a suitable raw material to produce smart packaging films. However, the application of SPSP-based films is restricted by the low antimicrobial activity of anthocyanins. In this study, SPSP-based smart packaging films were produced by adding mandarin essential oil (MEO) as an antimicrobial agent. The impact of MEO content (3%, 6%, and 9%) on the structures, properties, and application of SPSP-based films was measured. The results showed that MEO created several pores within films and reduced the hydrogen bonding system and crystallinity of films. The dark purple color of the SPSP films was almost unchanged by MEO. MEO significantly decreased the light transmittance, water vapor permeability, and tensile strength of the films, but remarkably increased the oxygen permeability, thermal stability, and antioxidant and antimicrobial properties of the films. The SPSP-MEO films showed intuitive color changes at different acid-base conditions. The purple-colored SPSP-MEO films turned blue when chilled shrimp and pork were not fresh. The MEO content greatly influenced the structures, physical properties, and antioxidant and antimicrobial activities of the films. However, the MEO content had no impact on the color change ability of the films. The results suggested that SPSP-MEO films have potential in the smart packaging of protein-rich foods.

Quercetin is a flavonoid with significant biological and pharmacological activity. In this paper, quercetin was modified at the 3-OH position. Rutin was used as a raw material. We used methyl protection, Williamson etherification reactions, and then substitution reactions to prepare 15 novel quercetin derivatives containing a quinoline moiety. All these complexes were characterized by ¹H NMR, ¹³C NMR, IR and HRMS. Of these, compound 3e (IC₅₀ = 6.722 μmol·L⁻¹) had a better inhibitory effect on human liver cancer (HepG-2) than DDP (Cisplatin) (IC₅₀ = 26.981 μmol·L⁻¹). The mechanism of the action experiment showed that compound 3e could induce cell apoptosis.

The high hydrophilicity of biopolymer–anthocyanin intelligent packaging films seriously limits their applications in high-humidity environments. Here, a surface hydrophobization technique was adopted to overcome the hydrophilicity of purple sweet potato (PSP)-based intelligent packaging films through stearic acid (SA) coating combined with heat pressing treatments. The structural characteristics, physical properties, and color changeability of the films were investigated. After SA coating treatment, the surface of the films was loosely covered by thick SA layers. As compared with the untreated PSP films, the SA-coated films displayed lower transparency, mechanical property, moisture content, surface wettability, anthocyanin leaching potential, and color changeability. When the SA-coated films were further heat-pressed, the SA-coated layers were closely bound to the films. The heat-pressed films had a higher transparency, mechanical property, and water vapor blocking ability than the SA-coated films. Notably, the color and color changeability of the heat-pressed films were affected by the heat pressing temperature. The films heat-pressed at 100 °C showed a vivid purple color and elevated color changeability, whereas the films heat-pressed at 150 °C showed a brown color and lost color changeability. This study demonstrates that SA coating combined with heat pressing is effective in constructing surface-hydrophobized intelligent packaging films.