Combined effects of drying methods, extract concentration, and film thickness on efficacy of antimicrobial chitosan films.

An idea of using a suitable drying method to minimize the loss of added antimicrobial agent and, at the same time, to modify the structure, and hence the release characteristics of chitosan films was proposed. Chitosan film-forming solution was incorporated with galangal extract (0% and 1.5% w/w) and formed into films with the thickness of 15 and 30 μm via hot air drying (HD) (40 °C) and low-pressure superheated steam drying (LPSSD) (70 °C, 10 kPa). The extract retention, release characteristics, and antimicrobial efficacy of the films were then assessed; fresh-cut cantaloupe was used as the test food material, while Staphylococcus aureus was the test pathogenic microorganism. The retention and release of 1,8-cineole, a major bioactive compound in the galangal extract, was monitored during 5-d storage at 25 °C. The film swelling was also evaluated and their results used to interpret the release characteristics of 1,8-cineole from the films to the cantaloupe. At the same thickness, the films prepared by HD had lower extract retention and higher degree of swelling, thus exhibiting faster extract release and lower antimicrobial efficacy than the films prepared by LPSSD. Within the same drying method, the increased film thickness led to higher extract retention and antimicrobial efficacy. The concentration of the extract in the cantaloupe matched well with the extract retention and release characteristics as well as the antimicrobial efficacy of the films. The results of this work illustrate the feasibility of using a suitable drying technology to improve the quality of antimicrobial films from edible biopolymer and form the basis for future development of an improved antimicrobial film production process.