Holocellulose nanofibrils as effective nisin immobilization substrates for antimicrobial food packaging

Holocellulose nanofibrils (HCNF), a type of nanocellulose with abundant amorphous regions suitable for chemical modification, show promise for sustainable food packaging but remain underutilized. This study employed HCNF to immobilize nisin and then spray-coated on the surface of soy protein isolate (SPI) films to improve mechanical, barrier, and antimicrobial properties. HCNF was extracted from wood sheet through chemical delignification and low-energy defibrillation, and then oxidized to introduce aldehyde groups for efficient nisin conjugation. The abundant amorphous regions led to a high immobilization rate of 3.4 mg/g, and conjugated HCNF and nisin coatings on SPI films significantly enhanced tensile strength to 3.43 ± 0.09 MPa, reduced water vapor permeability to 2.48 ± 0.07 × 10^-6 g m^-1 h^-1 Pa^-1, and decreased oxygen permeability to 4.29 ± 0.46 × 10^-4 cm³ m^-1 day^-1 atm^-1. The conjugate sustained inhibition of S. aureus and L. monocytogenes, and the coating of 9 wt% conjugate on SPI films resulted in a 6-log reduction in bacterial count for both bacteria, while free nisin lost its antimicrobial efficacy during 24 h of pre-incubation. This work suggests feasibility of using HCNF as an effective substrate for nisin immobilization, providing a sustainable functional packaging solution with extended antimicrobial activity.