• β-Chitosan films;
  • antibacterial activity;
  • mechanical properties;
  • monocarboxylic acid;
  • plasticizer;
  • water vapor permeability

Abstract:  Effects of chitosan molecular weight (1815 and 366 kDa), type of acid (1% acetic, formic, and propionic acid, or 0.5% lactic acid) and plasticizer (0, 25% glycerol or sorbital w/w chitosan) on the mechanical, water barrier, and antibacterial properties of β-chitosan films were investigated. Tensile strength (TS) of high molecular weight (Hw) films was 53% higher than that of low molecular weight (Lw) ones, acetate, and propionate films had the highest TS (43 and 40 MPa) among tested acids, and plasticizer-reduced film TS 34%. Film elongation at break (EL) was higher in Hw films than in Lw ones, in which formate and acetate films were the highest (9% and 8%, respectively), and plasticizer increased the film EL 128%. Molecular weight of chitosan did not influence water vapor permeability (WVP) of the films. Acetate and propionate films had lower WVP than other acid types of films, and plasticizer increased film WVP about 35%. No difference was found between glycerol and sorbitol films in terms of film mechanical and water barrier properties. Lw β-chitosan films showed significant antibacterial activity against E. coli and L. innocua. This study demonstrated that β-chitosan films are compatible to α-chitosan films in physicochemical properties and antibacterial activity, yet with simple sample preparation.

Practical Application:  β-chitosan based edible films at molecular weight of about 300 kDa showed great antibacterial activity against Gram-positive and Gram-negative bacteria. The films have similar mechanical and water barrier properties to α-chitosan based films at the similar molecular weight, but simple sample preparation procedures and more attractive color. The release of active chitosan fragment from the film matrix acts as an antibacterial agent, making β-chitosan films suitable as intelligent food wraps or coatings for a wide range of food products to control moisture loss and prevent surface bacterial growth.