Influence of droplet size on the antibacterial efficacy of citral and citronella oil nanoemulsions in polysaccharide coated fresh-cut apples

Fresh-cut fruits are highly perishable and susceptible to bacterial contamination. Polysaccharides edible coating loaded with essential oils nanoemulsions have the potential to extend shelf life and improve quality of fruits. The effectiveness of this approach is dependent on the properties of the nanoemulsions, such as droplet size (DS) and stability. This study aimed to optimize the production of citral (CT) and citronella oil (CTO) nanoemulsions (CT-CTO-NEs) incorporated in edible coating film to be used as natural antimicrobial agent in fresh-cut apples. After testing different combinations of surfactant (tween 80) and cosurfactant (propylene glycol) to obtain stable oil-in-water (o/w) nanoemulsions, the results demonstrated that optimized CT-CTO-NEs with DS less than 500 nm have been successfully achieved with high stability for 3 weeks at 4 °C. In addition, CT-CTO-NEs were obtained by In situ formation under magnetic stirring without applying complex high shear homogenization processes. Desired stability of CT-CTO-NEs also has been achieved within semi-solid matrix (sodium alginate cross-linked film). The relationship between DS and antibacterial activity was observed, with the smallest DS (< 100 nm) showing the highest antibacterial efficacy against Listeria monocytogenes and Escherichia coli. These results emphasize the importance of DS in the effectiveness of CT-CTO-NEs as an antibacterial coating for fresh-cut fruits.