Nanocellulose/Nisin Hydrogel Microparticles as Sustained Antimicrobial Coatings for Paper Packaging

Hydrogels composed of biomaterials are promising drug delivery systems. In this study, we prepared an antibacterial hydrogel by incorporating the antimicrobial peptide nisin into bagasse cellulose nanofibrils, followed by mechanic shearing to obtain hydrogel microparticles as antimicrobial coatings for paper packaging. The concept of combining nisin with a hydrogel network helps to reduce the nisin depletion disadvantage in a nisin alone coating while achieving a prolonged antibacterial efficacy in application. First, antimicrobial hydrogels were constructed by electrostatic attraction between TEMPO-oxidized cellulose nanofibrils (TOCNF) and nisin. The rheological analysis confirmed that the hydrogel with a TOCNF/nisin ratio of 3:1 formed a good gel network accompanied by a high nisin loading efficiency. The obtained hydrogel exhibited controlled release of nisin in response to pH, with a slower rate at pH 7 than that of pH 5 and pH 9. Then, the obtained hydrogel has been processed to microparticles to facilitate its application as coating on paper packaging. Highly stable TOCNFs/nisin hydrogel microparticles were obtained under a water/hydrogel ratio of 4:1 and a mechanical shearing rate of 8000 rpm. The paper with hydrogel microparticles coating displayed an enhanced tensile strength by 14.67% compared to uncoated paper. As a packaging for cheese in storage at 4 °C for 7 days, the hydrogel microparticle coating paper can significantly reduce the growth of Listeria monocytogenes on the surface of cheese and show a sustained inhibition advantage over a nisin alone coating. The utilization of hydrogel microparticles as the coating slurry provides a versatile approach for paper treatment and endows the paper with a sustained release characteristic in actively preventing the bacterial proliferation on food surfaces during storage. The finding from this work is expected to broaden the application of nanocellulose and nisin into the field of food active packaging.