Antimicrobial Paper Coatings Containing Microencapsulated Cymbopogon citratus Oil

Abstract

Essential oils are environmentally friendly candidates for antimicrobial smart packaging systems. Encapsulation is needed to reduce their volatility and achieve controlled release. Within this study, the essential oil of Cymbopogon citratus (citronella oil) was microencapsulated and applied in pressure-sensitive antimicrobial functional coatings on papers for secondary packaging. Two microencapsulation methods were used: complex coacervation of gelatine with carboxymethylcellulose or with gum arabic, and in situ polymerization of melamine-formaldehyde prepolymers with a polyacrylic acid modifier. Minimum inhibitory concentrations of citronella oil microcapsules were determined for Bacillus subtilis (B. subtilis), Escherichia coli (B. subtilis), Pseudomonas aeruginosa (P. aeruginosa) and Saccharomyces cerevisiae (S. cerevisiae). Microcapsule suspensions were coated on papers for flexible packaging, 2 and 30 g/m2, and mechanically activated in the weight pulling test. A novel method on agar plates in sealed Petri dishes was developed to evaluate the antimicrobial activity of released citronella vapours on E. coli and S. cerevisiae. The results showed that both microencapsulation methods were successful and resulted in a container type single-core microcapsules. In situ microcapsule suspensions had better paper coating properties and were selected for industrial settings. The antimicrobial activity of 2 g/m2 coatings was not detected; however, the antimicrobial activity of 30 g/m2 partially activated coated papers was confirmed. The product enabled a prolonged use with the gradual release of citronella oil at multiple exposures of functional papers to pressure, e.g., by a human hand during product handling.