Mechanically robust, nanofibers-anchored small molecule hybrid plant protein materials with improved antibacterial activity

Soy protein isolate (SPI)-based nanocomposites are highly susceptible to degradation by microorganisms. To overcome this, this study explored the effects of incorporating curcumin into SPI-based nanocomposite films on the antimicrobial properties of the films. Cellulose nanofibril (CNF) was brushed with cetyltrimethylammonium chloride (CTAC) to prepare the modified drug-carrier system to better enable the binding of the lipophilic curcumin. Manifested by the strong hydrophobic interactions between curcumin and the CTAC molecules, curcumin was successfully loaded onto the modified CNF with encapsulation efficiency and loading amount of 97.79% and 9.78 mg/g, respectively. The curcumin hybrid film exhibited satisfactory antibacterial properties against E. coli and S. aureus due to the sustained release of curcumin, and they exhibited high antioxidant activities based on DPPH assays. The curcumin release rates were dependent on the solvent polarity; the release was faster in the 80% (v/v) and 50% (v/v) ethanol solutions than in the 20% (v/v) ethanol solution, and was diffusion-controlled. The oxidation of the CNF by sodium periodate before modification and loading resulted in the formation of dialdehyde groups that enabled Maillard reactions to occur with lysine residues of SPI peptides, which endowed films with desirable mechanical properties, including a maximum tensile strength of 11.86 MPa. This work broadened the research on the exploration of nanofiber-carrier systems for drug-loading/releasing to develop green composite films with strong antibacterial and mechanical properties.