Development and Characterization of Biopolymer-based Composite Edible Films with Antimicrobial Functionality

Abstract

The modern food processing industry has undergone various changes during the past decade in terms of preservation and food safety. Novel preservation strategies such as innovative thermal processing, microwaves, irradiation, high-pressure, and pulsed electric fields have become more prevalent in the recent past. Though these techniques have demonstrated certain advantages such as reduced processing times and maintenance of food quality, several disadvantages are associated. For example, such processing technologies involve a high start-up cost which might be a hindrance for small-scale food processors. In addition, post-processing contamination of foods from spoilage and pathogenic microbes have also posed an increased threat within the food supply. Therefore, in order to maintain food quality and safety standards, alternative strategies need to be developed. One viable option is by the development of edible films. Edible films are prepared from biodegradable polymers and can be made functional by the addition of active ingredients such as antimicrobial agents. Therefore, the overall goal of this work is geared towards formulation and characterization of antimicrobial, composite, edible films from biodegradable polymers.
In the first part of the work, a biphasic edible film based on sago starch and guar gum was developed, and thereafter, two essential oils, namely, carvacrol (0.75% w/w) and citral (1.0% w/w) were impregnated either individually or in combination into the blend. The morphology, optical, structural, and water barrier properties of the films were evaluated by various analytical techniques. Scanning electron micrographs exhibited the roughness on the top surface of the essential oil-incorporated blend films, whereas the confocal microscopy confirmed the dispersibility of essential oils into the blend. The tensile strength of films significantly reduced and Young’s modulus increased when essential oils were incorporated. The sago starch/guar gum/essential oil films exhibited excellent antimicrobial activity against Bacillus cereus and Escherichia coli. These results indicate that essential oils have the potential as antimicrobial agents in sago starch/guar gum films for use as active packaging materials in the food applications.
The aim of the second part of the work was to formulate antimicrobial films of guar gum, sago starch, and whey protein isolate. The essential oils, namely, carvacrol, citral and their combination were used as the model antibacterial compounds. The films became darker and brownish in color due to the entrapment of the oils. The surface of oil-entrapped films were more rough and coarse. Confocal micrographs affirmed the uniform distribution of the oil droplets within the biopolymeric network. However, the film formulation containing combination of carvacrol and citral demonstrated the lowest WVTR, highest tensile strength, and Young’s modulus. All oil-containing films demonstrated strong antibacterial potency against both Bacillus cereus and Escherichia coli.
In the final section of the work, essential oil containing ternary films of chitosan, guar gum, and whey protein isolate were prepared. Eugenol, carvacrol, and citral were used as the oil phase, either alone or in combination. The addition of essential oils decreased the water vapor transmission rate and tensile strength of the films. CLSM confirmed the presence of essential oil droplets within the biopolymer matrix. The essential oil containing films showed good antimicrobial activity, suggesting potential application in food packaging