Bioactive paper coatings containing clove essential oil, eugenol and cinnamon aldehyde

Abstract

Introduction and motivation Food quality and safety are major concerns for food industries, governments, and consumers. The main problems include microbial contamination and lipid/protein oxidation which increase the risk of foodborne illness and reduce the shelf life of food product s. Consumer demand and awareness have increased hugely urging to replace synthetic agents with natural active substances. Essential oils have long been recognized for their antibacterial, antifungal, and antioxidant properties. Due to the instability of es sential oils they cannot be directly added into the food packaging and require immobilization. Therefore, the immobilization of natural antimicrobial or antioxidant agents within biopolymer matrices has been shown to be important task when preparing active food packaging. In the present work the emulsions of clove essential oil, eugenol or cinnamon aldehyde and starch sodium octenyl succinate were formulated, applied on paper and antioxidant as well as antimicrobial properties of the coatings have been eval uated. Methodologies The aqueous emulsions consisting of 20 % (w/v) starch sodium otenylsuccinate and 2.5, 5 or 10 % (w/w) of clove essential oil, eugenol or cinnamon aldehyde were prepared by using rotor stator homogenizer at 12,000 rpm for 5 min. The active coatings were app lied on paper by using a coating technique. The antioxidant activity of emulsions and coated paper samples was assessed by using 2,2 diphenyl 1 picrylhydrazyl method. The antimicrobial activity of emulsions and coatings was determined by disc diffusion met hod. Results The aqueous emulsions containing 2.5, 5 and 10 percent (w/w) of active components were prepared and bioactive properties were investigated. The antioxidant properties studies of emulsions showed that high antioxidant activity was characteristic of clove es sential oil and eugenol emulsions. Moreover, all emulsions indicated bactericidal activity against reference strains Gram positive (Staphylococcus aureus, Listeria monocytogenes, Bacillus cereus) and Gram negative bacteria (Escherichia coli) as well as fun gicidal effect towards yeasts (Candida albicans). The antibacterial properties such as minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were investigated. The lowest values of MIC and MBC against selected microorganisms w ere determined for emulsion containing cinnamon aldehyde. For instance, the MIC of cinnamon aldehyde emulsion was 0.125 mg/ml and the MBC was 0.250 mg/ml against C. albicans. The active coatings were obtained by casting emulsions on paper. The antioxidant properties assessment revealed that high antioxidant activity was characteristic of clove essential oil emulsions coatings (76 92 %) and eugenol emulsions coatings (87 91 %), meanwhile, coatings containing cinnamon aldehyde showed quite low antioxidant activity (4 9 %). Antimicrobial activity of coated paper samples was evaluated by measuring the radius of the inhibition zones. The coatings containing cinnamon aldehyde had a greatest effect on studied microorganisms. It was established that paper coated with 10 % of cinnamon aldehyde emulsion h ad 15.50 mm, 10.82 mm, 18.71 mm and 18.32 mm of inhibition zone against C. albicans, S. aureus, E. coli and B. cereus, respectively. Significance of the work The results suggest that the cinnamon aldehyde emulsions could be used as effective natural antimicrobial agent, whereas eugenol emulsions as antioxidant in food packaging systems aiming to improve the quality and extend their shelf life of food products.