Active Chitosan-Based Film with Antimicrobial Property for Food Packaging Application

Abstract

This research was aimed to develop an active film from chitosan film incorporated with green tea extract to enhance antioxidant and antimicrobial properties in order to be used for food shelf life extension. The experiments were divided into 3 parts. Firstly, chitosan-based film preparation and modification were determined. The results suggested that the optimum chitosan films could be prepared from 2% chitosan in 1% acetic acid. However, the chitosan film was brittle and had low flexibility. Mechanical property of chitosan film was modified by adding different concentrations of glycerol, as a plasticizer, including 0, 10, 20, 30, 40 and 50% (w/w of chitosan). The effect of plasticizer concentration on the mechanical properties of the chitosan film was determined by measuring their tensile strength, elongation at break, thickness, surface colors and water vapor transmission rate. The results showed that 30% glycerol was the optimum concentration to improve flexibility, while maintaining tensile strength and other physical properties of the film. Secondly, chitosan-based film was incorporated with green tea extract (GT) in order to improve film’s antioxidant and antimicrobial properties. The optimum concentration of green tea extract was then determined by adding 0, 2, 5, 10 and 20% (w/v) of green tea in film-forming solution, and tensile strength, elongation at break, water vapor permeability (WVP), density, total phenolic compounds (TPC), radicals scavenging 2,2-diphenyl-1-picrylhydrazyl (DPPH) of the film were determined. Fourier Transform Infrared (FTIR) spectrometry was carried out to observe the potential modifications of the chitosan films when incorporated with GTE. The ability to inhibit Staphylococcus aureus TISTR 118, Salmonella enteritidis DMST 17368, Escherichia coli TISTR 780 and Pseudomonas fluorescens TISTR 358 was conducted using agar diffusion method. It was found that WVP and lightness (L) decreased, while density, TPC, DPPH scavenging activity, redness (a), and yellowness (b) increased with increasing green tea concentration. The results also showed that films containing green tea extract had inhibition zone and could inhibit bacterial growth underneath film, while chitosan-alone film had no inhibition zone. The results suggested that incorporation of GT into chitosan films improved mechanical and water vapor barrier properties and enhanced polyphenolic content, antioxidant activity and antimicrobial property of the films. Changes in the FTIR spectra of the chitosan films were observed when GTE was incorporated, suggesting some interactions occurred between amine group of chitosan and hydroxyl group of green tea polyphenols. Lastly, the chitosan film containing green tea extract (CGT-film) was used as an active film for shelf life extension of pork sausage. Qualities of pork sausages wrapped with CGT-film were compared with those wrapped with chitosan-alone film without green tea incorporation (C-film) and those without chitosan film wrapping (Control). Changes in the physical qualities including color values and texture, the chemical qualities including pH and thiobarbituric value (TBA), the microbiological qualities including total plate count, yeasts/moulds, and lactic acid bacteria were determined throughout the storage. The sensory qualities including odor, color, slime formation, and overall acceptance were also evaluated using Quantitative Descriptive Analysis. The results showed that samples wrapped with CGT-film had higher cutting force, lightness and yellowness values, but lower TBA and microbial growth than those wrapped with C-film and control. Based on microbiological analysis and sensory evaluation, control samples and those wrapped with C-film had shelf life of less than 12 and 20 days, respectively. Samples wrapped with GCT-film had better qualities than other samples and had shelf life of up to 20 days at 4℃. Incorporation of GT into chitosan film could enhance the antioxidant and antiomicrobial properties of the film. CGT-film reduced the lipid oxidation and inhibited microbial growth and, consequently, could maintain qualities and extended shelf life of the pork sausage.