Films of chitosan and chitosan-oligosaccharide neutralized and thermally treated: Effects on its antibacterial and other activities

• A new chitosan-based insoluble film with antimicrobial activity has been developed.
• Heat or neutralization decreased the solubility of chitosan films but caused a lost in their antimicrobial activity.
• Incorporation of COS in chitosan films increased their antimicrobial activity.

The present study focuses on the effects of heat and neutralization treatments on solubility, water vapour permeability and antimicrobial activity of chitosan (Ch) and chitosan/chitooligosaccharide (ChO)-based films. ChO films showed stronger antimicrobial activity against Escherichia coli, Bacillus cereus, Staphylococcus aureus, Serratia liquefaciens and Lactobacillus plantarum than Ch films, indicating that this effect is attributed to the presence of chitooligosaccharides (COS) in the films. Heat and neutralization treatments decreased significantly the solubility of chitosan films and gave rise to a sharp loss in their antimicrobial activity. The incorporation of COS in chitosan films increased the inhibitory effect against the studied microorganisms without affecting significantly the water vapour permeability of the films. Thus, it is possible to get a more insoluble chitosan film with high antimicrobial activity by means of incorporation of COS combined with heat or neutralization treatments.